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Nov 2005

Volume 23, Issue 6, pp. L17-3218

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Possible role of oxygen impurities in degradation of nc-TiN/a-Si3N4 nanocomposites

Stan Veprek, Pavla Karvankova, and Maritza G. J. Veprek-Heijman

J. Vac. Sci. Technol. B 23, L17 (2005); http://dx.doi.org/10.1116/1.2131086 (5 pages) | Cited 14 times

Online Publication Date: 23 November 2005

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The recently reported strong effect of minor oxygen impurities on the degradation of mechanical properties of superhard nc-TiN/a-Si3N4 can be, by analogy with similar effects known in metallic alloys, understood on the basis of a simple size effect of large O2− impurity species incorporated into the Si3N4 interface. The electronic effect of the O2− sites within the Si3N4 interface is also likely to play an important role in weakening the Si–N and, possibly to a lesser extent, also Ti–N bonds. A simple model which assumes that the strength (and hardness) of these materials is approximately proportional to the reciprocal surface coverage of the TiN nanocrystals by oxygen impurities shows a surprisingly good agreement with the measured data.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.72.S- Impurities in crystals

Light-emitting diodes with nickel substrates fabricated by electroplating

P. H. Chang, N. C. Chen, Y. N. Wang, C. F. Shih, M. H. Wu, T. H. Yang, Y. H. Tzou, and S. J. Wang

J. Vac. Sci. Technol. B 23, L22 (2005); http://dx.doi.org/10.1116/1.2110280 (3 pages) | Cited 4 times

Online Publication Date: 29 November 2005

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AlGalnP light-emitting diodes (LEDs) with electroplated nickel substrate have been successfully fabricated. The AlGalnP LEDs were initially grown on a GaAs temporary substrate. After removing or thinning the GaAs substrate and coating a Au/Ge layer, a 60 μm thick nickel layer was electroplated on the Au/Ge surface serving as the substrate. The results show that the electroplated nickel substrate is effective in the thermal dissipation capability and reflectivity. As compared to LEDs with a GaAs substrate, an increase in the light output by up to 88% has been obtained. Additionally, the proposed method is so reliable that light output degradation was less than 10% after 1500 h operation at 60 °C and 50 mA.
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85.60.Jb Light-emitting devices
81.15.Pq Electrodeposition, electroplating

Passivation of zinc–tin–oxide thin-film transistors

David Hong and John F. Wager

J. Vac. Sci. Technol. B 23, L25 (2005); http://dx.doi.org/10.1116/1.2127954 (3 pages) | Cited 16 times

Online Publication Date: 29 November 2005

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A methodology for the passivation of bottom-gate thin-film transistors (TFTs) utilizing zinc–tin–oxide as the channel layer and silicon dioxide as the passivation layer is presented. This methodology involves annealing of the TFT after channel layer deposition and an additional anneal after thermal evaporation of a SiO2 passivation layer. Passivated zinc–tin–oxide TFTs possess electrical characteristics equivalent to those of unpassivated, air-exposed devices. In contrast, TFT electrical performance is dramatically degraded if a zinc–tin–oxide TFT is covered with a dielectric layer and does not undergo both types of anneal. In addition to silicon dioxide, successful passivation of zinc–tin–oxide TFTs is accomplished using thermally evaporated calcium fluoride, germanium oxide, strontium fluoride, or antimony oxide as passivation dielectrics.
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81.65.Rv Passivation
85.30.Tv Field effect devices
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.72.Cc Kinetics of defect formation and annealing
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Thermal-induced formation of silver nanowires on titanium dioxide thin films

Ta-Kun Chen, Wen-Tai Chen, Min-Chi Yang, and Ming-Show Wong

J. Vac. Sci. Technol. B 23, 2261 (2005); http://dx.doi.org/10.1116/1.2083927 (5 pages) | Cited 2 times

Online Publication Date: 26 October 2005

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Silver nanowires are formed by the thermal reduction of an aqueous silver nitrate solution on the surface of TiO2 thin films. A variety of silver nanostructures including nanowires were prepared by variations in the crystallinity of TiO2 thin films and heat-treatment temperature. Under appropriate conditions, silver nanowires 30–100 nm in diameter and 1–50 μm in length were produced. The nanowires are found only on anatase TiO2 thin films, and the yield of nanowires increases with the anatase crystallinity. While other substrate materials, including rutile TiO2 films, silicon wafers, indium tin oxide glasses, quartz coupons, chemical-vapor deposited diamond thin films, and alloy films, were used under comparable conditions, no silver nanowires were observed. The formation of silver nanowires seems to be related to the photocatalytic properties of anatase TiO2.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
82.30.-b Specific chemical reactions; reaction mechanisms
81.40.Gh Other heat and thermomechanical treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry

Magnetoplasmons in a pair of armchair carbon nanotubes

C. H. Lee, C. W. Chiu, F. L. Shyu, and M. F. Lin

J. Vac. Sci. Technol. B 23, 2266 (2005); http://dx.doi.org/10.1116/1.2083928 (6 pages)

Online Publication Date: 26 October 2005

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The low-frequency magnetoelectronic excitations in a pair of armchair carbon nanotubes are studied within the self-consistent-field approach. The intertube Coulomb interactions would induce the coherent and incoherent plasmon modes. Their existence, intensity, frequency, and group velocity are investigated in detail. They are dominated by the transferred momentum, the intertube distance, the magnitude, and the direction of the magnetic field.
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73.22.Lp Collective excitations
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Co-gas impact of B2H6 plasma diluted with helium on the plasma doping process in a pulsed glow-discharge system

Shu Qin, Allen McTeer, and Y. Jeff Hu

J. Vac. Sci. Technol. B 23, 2272 (2005); http://dx.doi.org/10.1116/1.2083929 (6 pages) | Cited 6 times

Online Publication Date: 26 October 2005

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It has been reported that helium dilution of B2H6 in the plasma doping (PLAD) process can be used to control and minimize deposition phenomenon. In this article we quantify the impact of such dilution on boron doping and deposition under PLAD conditions appropriate for ultrashallow junction formation. The sheet resistance (RS) of the implanted wafers remains nearly constant when B2H6 is diluted with He up to 95%, although the retained B dose is reduced. Secondary ion mass spectroscopy profiles indicate that B profiles are deeper for higher dilution than for lower dilution due to less B deposition. The deeper B profiles contribute to a higher activation fraction during annealing due to the B solid solubility limit. This higher activation compensates for the reduction of the retained B dose. The plasma doping process of a pulsed glow-discharge system by using B2H6 diluted with 95% provides optimal conditions for minimizing deposition. This results in a higher doping rate and then higher throughput.
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52.77.Dq Plasma-based ion implantation and deposition
61.72.uf Ge and Si
64.75.-g Phase equilibria
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Self-assembled tungsten nanocrystals in high-k dielectric for nonvolatile memory application

S. K. Samanta, Zerlinda Y. L. Tan, Won Jong Yoo, Ganesh Samudra, Sungjoo Lee, L. K. Bera, and N. Balasubramanian

J. Vac. Sci. Technol. B 23, 2278 (2005); http://dx.doi.org/10.1116/1.2083930 (6 pages) | Cited 6 times

Online Publication Date: 26 October 2005

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Discrete midgap tungsten nanocrystals (W-NCs) embedded in atomic layer deposited hafnium aluminate (HfAlO) film were fabricated by a self-assembly method using sputtering followed by rapid thermal annealing and integrated into transistors for nonvolatile memory application. Transmission electron microscopy and single electron diffraction analysis revealed the formation of crystalline W-NCs ( ∼ 5 nm) embedded in an amorphous HfAlO matrix. Effects of deposition of thin Al2O3 on the formation of W-NCs were investigated. Al2O3 was found to be effective to retain the amorphous property of the underlying HfAlO, assisting to form uniformly distributed and small W-NCs. Electrical characterization of the Si/HfAlO/W-NCs/HfAlO structure based memory device showed that clear memory effects (1.8 V memory window at operating bias of 7 V) and good retention properties (50 mV/dec threshold voltage decay rate) originate from the charge storage of electrons in W-NDs and deep quantum well of W-NDs embedded in the HfAlO+Al2O3 high-k structure.
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84.30.Sk Pulse and digital circuits
61.72.Cc Kinetics of defect formation and annealing
85.30.-z Semiconductor devices

Enhancement of electroluminescence in GaN-based light-emitting diodes using an efficient current blocking layer

Ho Won Jang and Jong-Lam Lee

J. Vac. Sci. Technol. B 23, 2284 (2005); http://dx.doi.org/10.1116/1.2083931 (4 pages) | Cited 5 times

Online Publication Date: 26 October 2005

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Enhancement of electroluminescence in GaN-based light-emitting diodes (LEDs) was achieved using an efficient current blocking layer formed by postannealing. When a LED chip with Ni/Au pad on Ni/Au transparent p contact was annealed at 500 °C, the electroluminescence of the LED chip increased by 55%. The specific contact resistivity of metal contact below the p pad significantly increased due to indiffusion of Au and Ni atoms from the p pad to the contact interfacial region. As a result, an efficient current blocking layer could be formed below the p pad, enhancing the light output and decreasing the reverse leakage current of the LED chip. This result suggests that a further increase in the extraction efficiency of GaN-based LEDs can be easily obtained using the postannealing.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Effects of focused gallium ion-beam implantation on properties of nanochannels on silicon-on-insulator substrates

A. Pan, Y. L. Wang, C. S. Wu, C. D. Chen, and N. W. Liu

J. Vac. Sci. Technol. B 23, 2288 (2005); http://dx.doi.org/10.1116/1.2101599 (4 pages) | Cited 4 times

Online Publication Date: 27 October 2005

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Gallium dopants have been introduced into micrometer and nanometer sized silicon-on-insulator devices by means of focused ion beam maskless implantation. Structures of implanted devices before and after annealing have been characterized by cross-sectional transmission electron microscopy and Raman spectroscopy. The implanted/annealed micrometer devices exhibit uniformly lower electric resistance due to the presence of dopants; and the nanometer scale devices also show lower resistance but with a large device-to-device fluctuation. The fluctuation is likely to be the result of statistical nonuniformity in the spatial distribution of the end-of-range damage on the nanometer scale.
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61.80.Jh Ion radiation effects
61.72.up Other materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
78.30.Hv Other nonmetallic inorganics

Selective growth of vertical ZnO nanowires on ZnO:Ga/Si3N4/SiO2/Si templates

Cheng-Liang Hsu, Shoou-Jinn Chang, Hui-Chuan Hung, Yan-Ru Lin, Tsung-Heng Lu, Yung-Kuan Tseng, and I-Cherng Chen

J. Vac. Sci. Technol. B 23, 2292 (2005); http://dx.doi.org/10.1116/1.2101600 (5 pages) | Cited 7 times

Online Publication Date: 27 October 2005

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High density vertical single crystal ZnO nanowires were selectively grown on ZnO:Ga/Si3N4/SiO2/Si templates at various temperatures by a two-step oxygen injection process of self-catalyzed vapor-liquid-solid (VLS) technology. It was found that tips of the ZnO nanowires are hexagonal. It was also found that average length of the ZnO nanowires increased while the average tip diameter of the ZnO nanowires decreased as the growth temperature increased. Furthermore, it was found that the ZnO nanowires grown at 500 °C were “tube-shaped” while the ZnO nanowires grown at 700 °C were “cone-shaped.” Photoluminescence (PL), x-ray diffraction (XRD), and energy depersive x-ray (EDX) results all indicate that the quality of our ZnO nanowires is good.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
78.55.Et II-VI semiconductors

Tip characterization and surface reconstruction of complex structures with critical dimension atomic force microscopy

G. Dahlen, M. Osborn, N. Okulan, W. Foreman, A. Chand, and J. Foucher

J. Vac. Sci. Technol. B 23, 2297 (2005); http://dx.doi.org/10.1116/1.2101601 (7 pages) | Cited 27 times

Online Publication Date: 27 October 2005

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This paper presents the first known image reconstruction of complex probe tip shapes and the removal of those shapes from reentrant topologies that are encountered in critical dimension (CD) measurements. Algorithm improvements are described that enable reentrant image reconstruction. In addition, a solution is presented which eliminates image artifacts that result from noise when using Legendre transform or “slope-matching” reconstruction techniques. The new methods are compared to existing technology and demonstrated on reentrant features. Although demonstrated with two-dimensional profiles, the methods are readily extendable to three-dimensional morphologies. Tip wear effects on CD measurement are investigated and compared with the previous state-of-the-art method (“tip width subtraction”) and fully reconstructed images, clearly showing superior measurement stability for the image reconstruction method. Finally, CD measurements derived from reconstructed images are compared directly with Hitachi S4000 and S5000 cross-section SEM (X-SEM) data. The results show a close match between the SEM and CD AFM data.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Lh Atomic force microscopes

Effect of a thin W interlayer on the thermal stability and electrical characteristics of NiSi film

Wei Huang, Li-Chun Zhang, Yu-Zhi Gao, Han-Yan Jin, Bao-Jun Ning, and Guang-Qin Zhang

J. Vac. Sci. Technol. B 23, 2304 (2005); http://dx.doi.org/10.1116/1.2101647 (5 pages) | Cited 2 times

Online Publication Date: 27 October 2005

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A silicide method was for the first time studied to improve the thermal stability of nickel monosilicide by adding a thin W interlayer within the nickel film. The results show that after rapid thermal annealing (RTA) at temperatures ranging from 650 °C to 800 °C, the sheet resistance of formed Ni(W)Si samples was lower than that of nickel monosilicide without the interlayer. X-ray diffraction (XRD) and raman spectra results both reveal that only the NiSi phase exists in these samples, but the high resistance NiSi2 phase does not. According to the Gibbs free energy theory, the incorporation of a 7.3 atomic ratio of the W element in the ternary silicide can delay the appearance of the high resistivity NiSi2 phase, and thus enhance the thermal stability of the NiSi film. Fabricated Ni(W)Si/Si Schottky barrier diodes displayed good quality, with the barrier height being located generally between 0.64 eV and 0.66 eV and the ideality factor approaching unity. This further shows that the presence of the W interlayer in nickel silicide is effective in promoting the thermal stability and electrical characteristics of nickel monosilicide.
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73.61.At Metal and metallic alloys
73.30.+y Surface double layers, Schottky barriers, and work functions
65.40.G- Other thermodynamical quantities
61.72.Cc Kinetics of defect formation and annealing
78.30.Er Solid metals and alloys
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Spatially selective immobilization of ferritin using solid–solution interfacial interactions

Edward Manning and Siu-Tung Yau

J. Vac. Sci. Technol. B 23, 2309 (2005); http://dx.doi.org/10.1116/1.2101677 (5 pages) | Cited 4 times

Online Publication Date: 27 October 2005

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Spatially selective immobilization of ferritin, an iron-storage protein, on a silicon surface using a Si–SiO2 template is demonstrated. The material-specific immobilization of the protein is achieved by controlling physical forces at the solution–solid interface between a ferritin solution and the template. The electrostatic interaction and hydrophobic interaction between ferritin molecules and the two kinds of materials of the template can be tuned to achieve adsorption of ferritin only on Si. This method was used to generate spatially confined assemblies of ferritin on the nanoscale and on the micron scale.
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87.80.-y Biophysical techniques (research methods)
87.14.E- Proteins
36.20.-r Macromolecules and polymer molecules
68.47.Fg Semiconductor surfaces
81.16.Rf Micro- and nanoscale pattern formation

Study of the buffer-layer and annealing-temperature impact on fabrication of polycrystalline Fe3O4 film for the application of spintronic devices

Xiao-Li Tang, Huai-Wu Zhang, Hua Su, and Zhi-Yong Zhong

J. Vac. Sci. Technol. B 23, 2314 (2005); http://dx.doi.org/10.1116/1.2101635 (5 pages) | Cited 3 times

Online Publication Date: 31 October 2005

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Polycrystalline Fe3O4 film grown directly on a Si(100) substrate and on a tantalum (Ta) buffer layer have been prepared by direct current (dc) magnetron-reactive sputtering and vacuum annealing under an infrared-lamp furnace system. The Fe3O4 quality was examined by x-ray diffraction (XRD). The results showed that the polycrystalline Fe3O4 films fabricated on a Ta buffer layer were better than directly sputtering the film on a Si substrate after annealing. The annealing temperatures were also investigated carefully. The optimum annealing temperature was found at 300 °C. The negative magnetoresistance was tested in polycrystalline Fe3O4, and showed a very weak saturation trend in the magnetic field up to 400 Oe.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.40.Gh Other heat and thermomechanical treatments
75.47.Pq Other materials

Maximum achievable aspect ratio in deep reactive ion etching of silicon due to aspect ratio dependent transport and the microloading effect

Junghoon Yeom, Yan Wu, John C. Selby, and Mark A. Shannon

J. Vac. Sci. Technol. B 23, 2319 (2005); http://dx.doi.org/10.1116/1.2101678 (11 pages) | Cited 16 times

Online Publication Date: 31 October 2005

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When etching high-aspect-ratio silicon features using deep reactive ion etching (DRIE), researchers find that there is a maximum achievable aspect ratio, which we define as the critical aspect ratio, of an etched silicon trench using a DRIE process. At this critical aspect ratio, the apparent etch rate (defined as the total depth etched divided by the total elapsed time) no longer monotonically decreases as the aspect ratio increases, but abruptly drops to zero. In this paper, we propose a theoretical model to predict the critical aspect ratio and reveal its causal mechanism. The model considers aspect ratio dependent transport mechanisms specific to each of the reactant species in the three subprocesses of a time-multiplexed etch cycle: deposition of a fluorocarbon passivation layer, etching of the fluorocarbon polymer at the bottom of the trench, and the subsequent etching of the underlying silicon. The model predicts that the critical aspect ratio is defined by the aspect ratio at which the polymer etch rate equals the product of the deposition rate and the set time ratio between the deposition and etching phases for the time-multiplexed process. Several DRIE experiments were performed to qualitatively validate the model. Both model simulations and experimental results demonstrate that the magnitude of the critical aspect ratio primarily depends on (i) the relative flux of neutral species at the trench opening, i.e., the microloading effect, and (ii) aspect ratio dependent transport of ions during the polymer etching subprocess of a DRIE cycle.
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81.65.Cf Surface cleaning, etching, patterning
68.47.Fg Semiconductor surfaces
52.77.Bn Etching and cleaning
81.65.Rv Passivation

Ohmic contact formation mechanism of Ta/Al/Mo/Au and Ti/Al/Mo/Au metallizations on AlGaN/GaN HEMTs

Fitih M. Mohammed, Liang Wang, Deepak Selvanathan, Hubert Hu, and Ilesanmi Adesida

J. Vac. Sci. Technol. B 23, 2330 (2005); http://dx.doi.org/10.1116/1.2101691 (6 pages) | Cited 10 times

Online Publication Date: 31 October 2005

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A comparative study of Ta/Al/Mo/Au and Ti/Al/Mo/Au metallizations for AlGaN/GaN high electron mobility transistors is presented. By the optimization of surface treatment schemes and annealing temperature, contact resistances of 0.172 and 0.228 Ω mm, and specific contact resistivities of 2.96×10−7 and 1.09×10−6 Ω cm2 were obtained for Ti/Al/Mo/Au and Ta/Al/Mo/Au, respectively. Auger electron spectroscopy (AES), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were utilized to study microstructural changes occurring in the metallization layers as a result of heat treatment. Results indicate dynamic systems of severe intermixing between atoms from the metallization layers and epilayers resulting in changes in surface morphology, as determined by atomic force microscopy (AFM). The formation of intermetallics and interfacial compounds was observed. The combined effect of surface treatment and annealing-induced reaction is proposed as the mechanisms for low-resistance Ohmic contact formation.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
68.35.Fx Diffusion; interface formation
73.40.Ns Metal-nonmetal contacts
81.65.-b Surface treatments
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential
68.37.Lp Transmission electron microscopy (TEM)
68.47.De Metallic surfaces
68.37.Ps Atomic force microscopy (AFM)

Operation of nanocrystalline silicon ballistic emitter in low vacuum and atmospheric pressures

Toshiyuki Ohta, Akira Kojima, Hiroyuki Hirakawa, Tadashi Iwamatsu, and Nobuyoshi Koshida

J. Vac. Sci. Technol. B 23, 2336 (2005); http://dx.doi.org/10.1116/1.2102928 (4 pages) | Cited 11 times

Online Publication Date: 31 October 2005

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To make the specific features of nanocrystalline silicon (nc-Si) cold cathode clear, its emission characteristics are investigated in low vacuum and atmospheric pressure. The experimental nc-Si diode is composed of a thin Au film, a nanocrystallized polysilicon layer, an n-type silicon wafer, and a back contact. It is shown that the ballistic electron emission mode of the nc-Si device is kept alive until the vacuum pressure is increased to about 10 Pa, and that a significant current signal is detected at the collector even in air. The current observed in air can be interpreted as a result of energetic electron attachment into oxygen molecules in proximity to the front surface. The effectiveness of this emitter for the use in air is applied to surface charging of an insulating polymer. The experimental results demonstrate that the surface of a polymer film located in air at a distance of 1 mm from the device surface is quickly charged up to a certain negative potential determined from the collector voltage. The surface-emitting nc-Si ballistic emitter is useful not only in vacuum, but also in air and gas ambient for various applications.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption
85.30.Kk Junction diodes

Pattern-dependent microloading and step coverage of silicon nitride thin films deposited in a single-wafer thermal chemical vapor deposition chamber

Jacob W. Smith, Sean M. Seutter, and R. Suryanaryanan Iyer

J. Vac. Sci. Technol. B 23, 2340 (2005); http://dx.doi.org/10.1116/1.2102947 (7 pages) | Cited 1 time

Online Publication Date: 31 October 2005

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Less than 10% pattern-dependent microloading and greater than 95% step coverage are required for low temperature deposition of Si3N4 spacer and etch stop films in advanced logic and dynamic random access memory semiconductor applications. A single-wafer chemical vapor deposition chamber was utilized to analyze pattern loading effect on 130 nm and 90 nm patterned wafers. With silane-ammonia chemistry as the focus, a variety of processing methods were employed utilizing continuous and cyclical deposition modes. In addition, methods to modify diffusion and/or reaction rates were studied, such as remote plasma excitation and carrier gas modifications. Finally, chemistry-related variables were evaluated by changing the Si-source precursor. It was concluded that process chemistry and specifically precursor is the most dominant factor determining pattern loading effect.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
81.16.Rf Micro- and nanoscale pattern formation
81.05.Hd Other semiconductors
66.30.-h Diffusion in solids

Physical characterization of ZnO nanorods grown on Si from aqueous solution and annealed at various atmospheres

Chih-Cheng Yang, San-Yuan Chen, and Hsin-Yi Lee

J. Vac. Sci. Technol. B 23, 2347 (2005); http://dx.doi.org/10.1116/1.2102967 (4 pages) | Cited 2 times

Online Publication Date: 31 October 2005

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High-density ZnO nanorods were vertically grown on Si coated with ZnO film (ZnO/Si substrate) from aqueous solution at low temperatures. The ZnO nanorods after annealed in various atmospheres still present good c-axis crystalline character but exhibit remarkable differences in photoluminescence (PL) properties. Enhancement of PL properties due to N2-atmosphere annealing for ultraviolet emission can be attributed to the reduction of defect density because the nonparamagnetic singly ionized state (N−) can easily occupy the oxygen vacancies as evidenced by Raman spectroscopy and electron paramagnetic resonance spectrometry. The extended x-ray absorption fine structure reveals that the annealing atmosphere shows no apparent influence on the deep-level defects of ZnO nanorods except that some ions are possibly trapped or adsorbed on the surface of the ZnO nanorods.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.70.Dm X-ray absorption spectra
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
71.55.Gs II-VI semiconductors
76.30.-v Electron paramagnetic resonance and relaxation

Observations of interfaces in direct wafer-bonded InP–GaAs structures

Yan-feng Lao, Hui-zhen Wu, and Ming Li

J. Vac. Sci. Technol. B 23, 2351 (2005); http://dx.doi.org/10.1116/1.2102968 (6 pages)

Online Publication Date: 31 October 2005

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Direct wafer-bonded InP–GaAs structures were studied by cross-sectional observations using a field-emission scanning-electron microscope (FESEM) and by infrared-absorbance spectra using a Fourier-transform infrared spectroscopy. FESEM observations demonstrate that the interfaces of 560 and 580 °C bonded InP–GaAs structures are smooth and uninterrupted, while interfacial gaps appear for the samples bonded at 620 and 680 °C. However, large dimensional areas of bonding interfaces cannot be observed by FESEM because its inspection size is limited to microregions. Experimental results show that infrared-absorbance measurements can be an effective method for quality examination of bonded InP–GaAs structures. By soaking wax into poorly bonded interfaces and using its absorption characteristics at 3.383, 3.426, and 3.509 μm, interfacial gaps are indirectly measured by infrared spectra. Absorbance-intensity mappings at absorption peaks were used to image poorly bonded areas. Thus the interface quality of the whole wafer-bonded sample can be seen clearly. Nonuniform pressure applied over the sample during annealing step accounts for poorly bonded interfaces. Using the improved fixture, uniformly bonded InP–GaAs structures that do not have interfacial gaps were obtained.
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81.05.Ea III-V semiconductors
68.35.Fx Diffusion; interface formation
78.30.Fs III-V and II-VI semiconductors

Passivation effects on the stability of pentacene thin-film transistors with SnO2 prepared by ion-beam-assisted deposition

Woo Jin Kim, Won Hoe Koo, Sung Jin Jo, Chang Su Kim, Hong Koo Baik, Jiyoul Lee, and Seongil Im

J. Vac. Sci. Technol. B 23, 2357 (2005); http://dx.doi.org/10.1116/1.2102969 (6 pages) | Cited 6 times

Online Publication Date: 31 October 2005

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The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO2 thin-film prepared by ion-beam-assisted deposition (IBAD) was investigated. When a buffer layer of 100-nm SnO2 film had been thermally deposited to reduce ion-induced damage prior to the IBAD process, our encapsulated organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm2/V that was initially 0.62 cm2/V s, while the OTFTs without a buffer layer showed a 60% reduction in field-effect mobility after the IBAD process. However, surprisingly, the mobility was sustained up to one month and then gradually degraded down to 0.35 cm2/V s, which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air. The encapsulated OTFTs also exhibited superior on/off current ratio of over 105 to that of the unprotected devices ( ∼ 104), which was reduced from ∼ 106 before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to good protection of permeation against H2O into the devices with the IBAD SnO2 thin film, which was identified as having a dense amorphous microstructure with lots of OH groups. Passivation effects on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of the barrier films.
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85.30.Tv Field effect devices
81.65.Rv Passivation
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Field emission of carbon nanotubes grown on carbon cloth

S. H. Jo, J. Y. Huang, S. Chen, G. Y. Xiong, D. Z. Wang, and Z. F. Ren

J. Vac. Sci. Technol. B 23, 2363 (2005); http://dx.doi.org/10.1116/1.2102970 (6 pages) | Cited 8 times

Online Publication Date: 31 October 2005

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Field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied. Iron sulfate or stainless steel was used as the catalyst, acetylene (C2H2) or methane (CH4) was used as the carbon source, and argon (Ar), hydrogen (H2), or ammonia (NH3) was used as the carrier gas. It is found that the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time. In general, higher temperature produces better field emitters than lower temperature, C2H2/Ar is better than C2H2/NH3, but CH4/H2 is the best, and longer growth time normally yields longer CNTs leading to better field emitters. The best sample was made from 0.18 mol/l iron sulfate catalyst with CH4/H2 at 860 °C for 2 h: an emission current density of 1 mA/cm2 was obtained at 0.4 V/μm corresponding to a field enhancement factor of 3.5×104.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.07.De Nanotubes

Effects of bonding materials in screen-printing paste on the field-emission properties of carbon nanotube cathodes

Heo-Young Shin, Won-Sub Chung, Kwang Ho Kim, Young-Rae Cho, and Byoung-Chul Shin

J. Vac. Sci. Technol. B 23, 2369 (2005); http://dx.doi.org/10.1116/1.2110342 (4 pages) | Cited 10 times

Online Publication Date: 31 October 2005

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The effects of bonding materials in screen-printing paste on field-emission properties were investigated with respect to high-efficient carbon nanotube (CNT) cathodes. The materials used to bond the CNTs to the cathode were composed of an insulating glass frit and a conducting Ag paste. The dependence of the electrical conductivity of the CNT paste, bonding material, and CNT ink on the field-enhancement factor was investigated using the Fowler–Nordheim equation. The emission current from the CNT cathode as the result of an electron tunneling effect was increased with increasing ratio of the dielectric glass-frit fraction in the CNT paste. The larger emission current of CNT cathode containing insulating-bonding materials can be attributed to a combination of the increased effective height of the CNTs, which protrude over the film in the cathode, and an increased field-enhancement factor.
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79.70.+q Field emission, ionization, evaporation, and desorption

Characterization of bulk GaN rectifiers for hydrogen gas sensing

Lars Voss, B. P. Gila, S. J. Pearton, Hung-Ta Wang, and F. Ren

J. Vac. Sci. Technol. B 23, 2373 (2005); http://dx.doi.org/10.1116/1.2110343 (5 pages) | Cited 13 times

Online Publication Date: 1 November 2005

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Pd and Pt Schottky diodes were fabricated on free-standing 2-in.-diameter GaN substrates prepared by a combination of hydride vapor phase epitaxy of ∼ 350 μm onto sapphire, substrate removal and subsequent growth of 3 μm of epi GaN by metalorganic chemical vapor deposition. Vertical diodes with Ti/Al/Pt/Au back contacts annealed at 850 °C for 30 s showed excellent rectification with an on/off ratio of ∼ 100 at 1.5 V/−10 V. Both forward turn-on and reverse breakdown voltages showed negative temperature coefficients. Pd and Pt diodes showed detection of 10 ppm H2 in N2 at 25 °C, with fast (<10 s) recovery times upon removal of hydrogen from the measurement ambient. The Pt showed higher detection sensitivity than Pd. Detection of C2H4 and C2H6 required much higher temperatures ( ∼ 450 °C) and concentrations (10%) of the gases in N2 than hydrogen detection.
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85.30.Kk Junction diodes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
61.72.Cc Kinetics of defect formation and annealing

Iridium/silicon capping layer for soft x-ray and extreme ultraviolet mirrors

Shon T. Prisbrey, Stephen P. Vernon, and W. Miles Clift

J. Vac. Sci. Technol. B 23, 2378 (2005); http://dx.doi.org/10.1116/1.2122727 (6 pages) | Cited 2 times

Online Publication Date: 1 November 2005

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Iridium terminated silicon spacer layers on Mo/Si multilayer mirrors fabricated by dc magnetron sputtering are investigated for temporal stability. Samples maintained in atmosphere for periods of more than 3000 hours show: Ir terminating layers >16 Å thick are stable, layers with thicknesses between ∼ 10 and 16 Å are not stable, and thicknesses between ∼ 7 and 10 Å are stable after a loss in reflectance of ∼ 1%. Extreme ultraviolet (EUV) reflectance, atomic force microscopy, sputter Auger electron spectroscopy, and x-ray diffraction measurements indicate that the terminating layer is, in reality, an alloy with graded composition that is Ir rich at the surface. The compositional gradient causes a degradation in reflectance from 66% for Si terminated multilayers to ∼ 63% for Ir terminated samples (thickness 18.7 Å). A sudden onset of oxidation induced silicon transport for deposited layers of Ir ∼ 10−16 Å thick produces a degradation in EUV reflectance upon exposure to atmosphere. Accelerated lifetime testing of Si and Ir (18.7 Å) terminated multilayer mirrors show a ΔR/R reflectance loss of 0.2% for the Ir terminated sample and ∼ 3% for the Si terminated sample. Further development on Ir terminated multilayer stacks to increase reflectance is needed.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
32.30.Rj X-ray spectra
33.20.Rm X-ray spectra

Temperature characteristics of stress-induced migration based on atom migration

Minoru Aoyagi

J. Vac. Sci. Technol. B 23, 2384 (2005); http://dx.doi.org/10.1116/1.2123447 (6 pages) | Cited 4 times

Online Publication Date: 1 November 2005

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Stress-induced migration is one of the problems associated with the reliability of metal interconnections in semiconductor devices. The physical model of stress-induced migration has been established as that of the migration of vacancies. Vacancies can be considered as holes among atoms constituting interconnections. To clarify the mechanism of stress-induced migration, an atomic migration model is more essential than the physical model. First, we present the stress-induced migration model based on atomic migration using simple calculations in detail. The key issue in this model is the change in elastic potential with atom migration. Second, the presented model is applied in simple cases for analyzing the stress relaxation time due to stress-induced migration. We found that the temperature characteristics of the stress relaxation time have some patterns depending on void surface stress, the stress in an interconnection, and void interval. These patterns reported concerning the interconnection lifetime due to stress-induced migration can be qualitatively explained by the presented model.
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66.30.Lw Diffusion of other defects

Magnetoresistance of patterned NiFe thin films with structures modified by atomic force microscope nanolithography

Genta Watanabe, Sinichi Koizumi, Tsutomu Yamada, Yasushi Takemura, and Jun-ichi Shirakashi

J. Vac. Sci. Technol. B 23, 2390 (2005); http://dx.doi.org/10.1116/1.2122767 (4 pages) | Cited 1 time

Online Publication Date: 1 November 2005

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Surfaces of patterned NiFe strip-shaped thin films of 15–30 nm thickness were modified by nanowires of NiFe oxide. The NiFe oxide was fabricated by the atomic force microscopy (AFM) nano-oxidation technique. The anisotropy magnetoresistance was measured in order to study the effect of the nanowires in the magnetization reversal process. The domain wall was pinned at the nanowires of the NiFe oxide. It was indicated that the propagation of domain wall could be controlled by the AFM nanolithography.
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81.07.Bc Nanocrystalline materials
75.50.Bb Fe and its alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Np Metals and alloys
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.16.Ta Atom manipulation
81.16.Pr Micro- and nano-oxidation
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.De Metallic surfaces
81.65.Mq Oxidation
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
68.55.-a Thin film structure and morphology

Fabrication and characterization of CuO nanorods by a submerged arc nanoparticle synthesis system

Chih-Hung Lo, Tsing-Tshih Tsung, and Liang-Chia Chen

J. Vac. Sci. Technol. B 23, 2394 (2005); http://dx.doi.org/10.1116/1.2122787 (4 pages) | Cited 4 times

Online Publication Date: 1 November 2005

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The purpose of this study is to investigate an innovative nanorod preparation method, the submerged arc nanoparticle synthesis system. The key parameters such as discharge current, breakdown voltage, pulse duration, and temperature of the dielectric liquid are carefully analyzed in order to obtain more uniform nanorods. The prepared nanorods were systematically characterized by x-ray diffraction, transmission electron microscopy, selected-area electron diffraction, x-ray photoelectron spectroscopy, and the ultraviolet-visible absorption spectrum. The results showed that the CuO nanorods had a diameter of 30–50 nm and a longitudinal length of up to 1–2 μm. A possible preparation mechanism was also discussed for the growth of the CuO nanorods.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
52.77.-j Plasma applications
77.22.Jp Dielectric breakdown and space-charge effects
68.37.Lp Transmission electron microscopy (TEM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
78.40.Ha Other nonmetallic inorganics

Preparation and characterization of titania nanotubes and hybrid materials derived from them

Yi-Jun Lin, Leeyih Wang, and Wen-Yen Chiu

J. Vac. Sci. Technol. B 23, 2398 (2005); http://dx.doi.org/10.1116/1.2122827 (5 pages) | Cited 2 times

Online Publication Date: 1 November 2005

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TiO2 nanotubes with outer diameters of ∼ 10 nm and lengths of several hundreds nanometer were synthesized by the hydrothermal method. The morphology of the nanotubes was thoroughly examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition and structure of tubular materials were determined by energy dispersive x-ray spectroscopy, selected area electron diffraction pattern, and x-ray diffraction (XRD). XRD results confirmed that the nanotubes are composed of pure anstase TiO2. Both TEM and the Barrett–Joyner–Halenda methods indicated that the inner diameters of the nanotubes are around 7 nm. In addition, the hybrid of poly(3-hexylthiophene) and TiO2 nanotube were prepared by the oxidative polymerization of 3-hexylthiophene in the presence of TiO2 nanotubes. The obtained composites were characterized by SEM, Fourier transformed infrared spectroscopy, and thermal gravimetric analysis.
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81.07.De Nanotubes
81.07.Pr Organic-inorganic hybrid nanostructures
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.46.-w Structure of nanoscale materials
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.35.-x Polymers: properties; reactions; polymerization
78.30.-j Infrared and Raman spectra

Nanoscale electron stimulated chemical vapor deposition of Au in an environmental transmission electron microscope

Sutharsan Ketharanathan, Renu Sharma, and Jeff Drucker

J. Vac. Sci. Technol. B 23, 2403 (2005); http://dx.doi.org/10.1116/1.2122847 (6 pages) | Cited 4 times

Online Publication Date: 1 November 2005

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Nanoscale Au rich dots were deposited on SiO2 and Si3N4 substrates by decomposing an adsorbed organometallic precursor using a focused electron beam. The precursor, dimethyl acetylacetonate gold ((CH3)2(C5H7O2)Au), does not react with either substrate without electron irradiation. Deposited feature diameters are larger than that of the electron beam used for deposition by an amount comparable to the secondary electron escape depth. This result suggests that axial secondary electron emission through the surface of a growing feature limits the minimum attainable feature size. Real-time composition analysis during growth using electron energy-loss spectroscopy indicates that mature features entrain significant carbon.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.80.Fe Electron and positron radiation effects
61.46.-w Structure of nanoscale materials
79.20.Uv Electron energy loss spectroscopy

Bubbles in immersion lithography

M. Switkes, M. Rothschild, T. A. Shedd, H. B. Burnett, and M. S. Yeung

J. Vac. Sci. Technol. B 23, 2409 (2005); http://dx.doi.org/10.1116/1.2122747 (4 pages) | Cited 1 time

Online Publication Date: 3 November 2005

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One of the major concerns in the emerging technology of liquid immersion lithography is the possibility of defects due to bubble formation in the immersion liquid. We have performed numerical simulations of the impact of bubbles on printing. The greatest impact is due to bubbles close to the resist surface; beyond several bubble diameters, the impact of a bubble is negligible. With this in mind, we have investigated one of the major candidates for producing near-surface bubbles, resist outgassing. We have imaged, with 0.25 μm/pixel resolution, the surface of an immersed resist immediately after exposure to 193 nm radiation at a fluence of 2–20 mJ/cm2. Using a high outgassing 248 nm resist, bubble formation is clear. However, in over 3000 frames of a model 193 nm immersion resist, only one frame with bubble candidates was seen, and only at a fluence (20 mJ cm−2) far exceeding that of normal exposure conditions.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Photosensitive quantum dot composites and their applications in optical structures

Lin Pang, Kevin Tetz, Yaoming Shen, Chyong-Hua Chen, and Yeshaiahu Fainman

J. Vac. Sci. Technol. B 23, 2413 (2005); http://dx.doi.org/10.1116/1.2122867 (6 pages) | Cited 11 times

Online Publication Date: 3 November 2005

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Commercially available CdSe/ZnS and PbSe colloidal semiconductor quantum dots were employed to produce both an electron beam sensitive poly(methyl methacrylate) (PMMA)-quantum-dot (QD) positive composite via a prepolymerization processing and an electron beam and ultraviolet (UV) light sensitive SU-8-QD negative composite via a direct dispersion procedure. Compared to the QDs in the original colloidal solutions, the photoluminescence of the composites shifts to shorter wavelength due to the oxidation of the surfaces of the QDs. Using the QD composites, optical integrated circuits such as grating and waveguide structures were fabricated by direct electron beam writing and UV optical lithography. The characterization results show promising applications in optoelectronics for the QD composites.
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78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
82.70.Dd Colloids
81.65.Mq Oxidation
85.30.-z Semiconductor devices
42.79.Dj Gratings
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
78.55.Et II-VI semiconductors
81.07.Ta Quantum dots

Modeling of protection schemes for critical surfaces under low pressure conditions: Comparison between analytical and numerical approach

Christof Asbach, David Y. H. Pui, Jung Hyeun Kim, Se-Jin Yook, and Heinz Fissan

J. Vac. Sci. Technol. B 23, 2419 (2005); http://dx.doi.org/10.1116/1.2122927 (8 pages) | Cited 10 times

Online Publication Date: 3 November 2005

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Nanoparticle contamination is one of the crucial issues for the semiconductor industry on the move towards structure sizes of 50 nm and below. In extreme ultraviolet lithography (EUVL), a likely successor to optical lithography, the masks cannot be protected by common pellicles. Different protection methods, such as a “thermophoretic pellicle” [ L. Klebanoff and D. J. Rader, US Patent No. 6,153,044 (2000) and US Patent No. 6,253,464 B1 (2001) ] have therefore been proposed to protect a face-down mask in an EUV scanner, which might be operated at 50 mTorr (6.7 Pa). In order to quantify the effectiveness of such protection schemes, we developed an analytical model that allows simple determination of the particle stopping distance as a function of particle and gas properties as well as a thermal gradient that might be employed to make use of a thermophoretic force in order to protect the mask. The analytical results indicate that drag force is most effective in slowing down particles, traveling at high initial velocities. Thermophoresis can add effective protection to particles traveling at low velocities and therefore decrease diffusional deposition. The results from the analytical model were used to check the accuracy of the discrete phase model in FLUENT for particle diameters between 100 and 500 nm and pressure levels between 10 mTorr (1.3 Pa) and 500 mTorr (66.7 Pa) (corresponding Knudsen numbers 407 ≤ Kn ≤ 102 000). The comparison results indicate that with no thermal gradient, the results agree very well with less than 2% deviation. If thermophoresis is included, the absolute deviation generally increases with increasing Knudsen number and with increasing temperature gradient. For a temperature gradient of 10 K/cm and a Knudsen number of 102 000 (p = 10 mTorr, dp = 100 nm), the deviation reaches almost 50% for 2 m/s initial particle velocity.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments

Numeric analysis of the role of liquid phase ultraviolet photochemistry in 193 nm immersion lithography

William Hinsberg and Frances Houle

J. Vac. Sci. Technol. B 23, 2427 (2005); http://dx.doi.org/10.1116/1.2126671 (9 pages) | Cited 2 times

Online Publication Date: 3 November 2005

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A quantitative evaluation of the photochemistry taking place in the water fluid layer during lithographic immersion exposure with 193 nm radiation is described. This analysis uses a detailed kinetic model based on available literature mechanistic data and constructed with in-house simulation tools. Product yields from the intrinsic photochemistry of pure, degassed water, the effects of trace quantities of dissolved oxygen and organics on these photochemical reactions, and the potential impact of reactive photoproducts on a photoresist film in contact with the fluid are estimated.
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85.40.Hp Lithography, masks and pattern transfer

Barrier height enhancement and stability of the Au/n-InP Schottky barrier diodes oxidized by absorbed water vapor

H. Çetin, E. Ayyildiz, and A. Türüt

J. Vac. Sci. Technol. B 23, 2436 (2005); http://dx.doi.org/10.1116/1.2126675 (8 pages) | Cited 10 times

Online Publication Date: 3 November 2005

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We have fabricated the Au/n-InP Schottky barrier diodes (SBDs) with and without an intentionally grown interfacial oxide layer. The oxide layer on chemically cleaned indium phosphide (InP) surface has been obtained by exposure to water vapor at 1 ml/min at 200 °C before metal evaporation. The chemical composition of the surface oxides grown on the InP is investigated using x-ray photoelectron spectroscopy. Phosphorus is present as In(PO3)3, InPO4, P2O5 and elemental P. The influence of the oxide on the Schottky barrier formation and contact stability at the InP (100) surface upon subsequent metal deposition has been investigated. The transport properties of the metal-semiconductor contacts have been observed to be significantly affected by the presence of the interfacial oxide layer. Thus, the barrier height has been increased by ∼ 140 meV for the Au/n-InP SBD by means of the interfacial oxide grown by use of absorbed water vapor. Furthermore, in order to observe the effect of the aging in the Au/n-InP SBD with and without the interfacial oxide layer, the current-voltage (I-V) measurements have also been repeated 7, 14, 28, 45, 56, and 70 days after fabrication of these diodes. The obtained diode parameters were examined statistically and it was found that the reference and oxidized Au/n-InP SBDs exhibited stable characteristics 14 days after metal deposition.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
81.65.Mq Oxidation

Formation of Ti–Si–N film using low frequency, high density inductively coupled plasma process

Y. C. Ee, Z. Chen, L. Chan, K. H. See, S. B. Law, S. Xu, Z. L. Tsakadze, P. P. Rutkevych, K. Y. Zeng, and L. Shen

J. Vac. Sci. Technol. B 23, 2444 (2005); http://dx.doi.org/10.1116/1.2131080 (5 pages) | Cited 2 times

Online Publication Date: 4 November 2005

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Titanium silicon nitride (Ti–Si–N) has emerged as a strong candidate for next generation diffusion barrier material in copper/low-k dielectric back-end-of-line device fabrication. Low frequency, high density inductively coupled plasma process has been developed for the growth of Ti–Si–N film. This work employs the reaction between TixSiy and the nitrogen plasma. Ti–Si–N films have been successfully grown over different process conditions. Film properties were characterized by Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy, x-ray diffraction (XRD), and four-point resistivity probe. RBS reveals that 2–67 at. % of nitrogen can be achieved through the implantation of nitrogen in TixSiy film. XPS and XRD results show that TiN and Si3N4 are successfully formed. As the external bias increases from 100 to 300 V, there is an 80% increase in sheet resistance. Other process conditions investigated do not show a significant effect on film sheet resistance. Increasing argon plasma activation time can significantly increase the implantation depth of nitrogen into TixSiy substrate.
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66.30.Ny Chemical interdiffusion; diffusion barriers
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.up Other materials
85.40.Ls Metallization, contacts, interconnects; device isolation

High-efficiency light-emitting device based on silicon nanostructures and tunneling carrier injection

Hei Wong, V. Filip, and P. L. Chu

J. Vac. Sci. Technol. B 23, 2449 (2005); http://dx.doi.org/10.1116/1.2131082 (8 pages) | Cited 2 times

Online Publication Date: 4 November 2005

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Light-emitting device structure (Si/SiO2/low-dimensional Si/Si3N4/Si) is proposed. The low-dimensional Si governed the photon generation efficiency and energy spectrum whereas the asymmetry barrier heights on both sides formed by the SiO2 and Si3N4, respectively, provide high-efficiency carrier injection based on direct tunneling and maximize the rate of the recombination events taking place in the low-dimensional silicon. Detailed theoretical modeling of carrier transportation in this device structure is developed. Theoretical calculations demonstrate that the recombination rate of carrier with this structure can be as high as 3×1023 cm−2 s−1 and are governed by the barrier heights, thickness of the dielectric films, and the width of low-dimensional Si region.
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85.60.Jb Light-emitting devices

Diamond nanorods

O. A. Shenderova, C. W. Padgett, Z. Hu, and D. W. Brenner

J. Vac. Sci. Technol. B 23, 2457 (2005); http://dx.doi.org/10.1116/1.2122907 (8 pages) | Cited 15 times

Online Publication Date: 7 November 2005

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Diamond nanorods are one-dimensional carbon nanostructures consisting of all sp3 bonded carbon atoms. They represent an alternative class of carbon structure to fullerene nanotubes for potential applications in nanocomposites for mechanical reinforcement and thermal management, as well as in microelectronics. Synthetic routes for creating diamond nanorods (and related structures) and recent predictions of their stability, mechanical, and thermal properties are summarized in the article.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Various driving modes of a field emission cathode

Y. S. Choi

J. Vac. Sci. Technol. B 23, 2465 (2005); http://dx.doi.org/10.1116/1.2126673 (6 pages) | Cited 1 time

Online Publication Date: 7 November 2005

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Characteristics of various driving modes in a field emission display with carbon nanotube emitters are investigated through computer simulations. In triode structural field emission displays electron emission from the cathode electrode is induced by the extraction of external electric fields due to the gate electrode and anode electrode. By the relative value of gate and anode field strengths on emission material the driving mode may divide into four categories of gate extraction, gate-anode extraction, anode-gate extraction, and anode extraction modes. According to our simulation results, the best performance would be produced by the gate-anode and the anode-gate extraction modes, in which the gate and anode fields on emission material are compatible in strength.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.35.Kt Nanotube devices

Nanoscale fabrication in aqueous KOH solution using tribo-nanolithography

Noritaka Kawasegi, Jeong Woo Park, Noboru Morita, Shigeru Yamada, Noboru Takano, Tatsuo Oyama, and Kiwamu Ashida

J. Vac. Sci. Technol. B 23, 2471 (2005); http://dx.doi.org/10.1116/1.2126674 (5 pages) | Cited 1 time

Online Publication Date: 7 November 2005

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A simple process to fabricate a three-dimensional structure on silicon surface was developed by using tribo-nanolithography (TNL) in an aqueous KOH solution. An inclined rectangular structure can be fabricated by a process where a thin amorphous layer, having corrosion resistance against KOH, rapidly forms on the substrate at the diamond tip sample junction along the scanning pass of the tip, while simultaneously, the area not covered with the amorphous layer is being etched in KOH. An inclination of structure can be controlled by the scanning velocity. The scanning pitch is related to the corrosion resistance of the amorphous layer, rather than the change of inclination. We fabricated a structure having multiple inclinations based on these results, which indicates the possibility of using the TNL for three-dimensional nanofabrication.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
81.65.Kn Corrosion protection

Wing-tilt-free gallium nitride laterally grown on maskless chemical-etched sapphire-patterned substrate

Jing Wang, L. W. Guo, H. Q. Jia, Z. G. Xing, Y. Wang, H. Chen, and J. M. Zhou

J. Vac. Sci. Technol. B 23, 2476 (2005); http://dx.doi.org/10.1116/1.2122807 (4 pages) | Cited 3 times

Online Publication Date: 11 November 2005

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A method is developed to overcome the problem of wing tilt that appears in lateral epitaxial overgrowth of GaN films. High-quality GaN films free of wing tilt were obtained reproducibly on wet chemical-etched maskless c-plane sapphire substrate using metalorganic chemical vapor deposition (hereafter called CantiBridge epitaxy). Symmetrical (0002) x-ray diffraction of a4.5-μm-thick GaN film is performed with the scattering plane parallel and perpendicular to the stripe direction. The corresponding full widths at half maxima of the (0002) peaks are about 147 and 144 arcsec, respectively, which is one of the best results reported to date. Scanning electron microscopy cross-section images show that GaN was selectively grown on the mesas and the lateral overgrowth GaN spanned the etched trenches. No GaN was found on the grooved sapphire trenches, which is very different from the usually observed phenomena in other lateral epitaxial overgrowth techniques. It is inferred that damage-free mesas and grooves benefit the elimination of wing tilt and they improve the quality of the lateral overgrown GaN. The results indicate that CantiBridge epitaxy is a promising technique for fabricating high-quality GaN-based materials and devices.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

Lanthanum aluminate by atomic layer deposition and molecular beam epitaxy

D. H. Triyoso, H. Li, R. I. Hegde, Z. Yu, K. Moore, J. Grant, B. E. White, and P. J. Tobin

J. Vac. Sci. Technol. B 23, 2480 (2005); http://dx.doi.org/10.1116/1.2131077 (6 pages) | Cited 3 times

Online Publication Date: 11 November 2005

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A comparison of physical and electrical characteristics of lanthanum aluminate (LAO) dielectrics formed by atomic layer deposition (ALD) and molecular beam epitaxy (MBE) is investigated in this study. Physical characteristics of LAO deposited with these two deposition methods are compared using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). Capacitors with TaN and TaSiN gate electrodes were fabricated to assess electrical properties of these LAO films. ALD LAO was deposited using La[N(SiMe3)2]3, Al(CH3)3 and water at 225–275 °C. ALD LAO is stable against Pt and TiN/W metal gates up to 800 °C. After annealing at 900 °C, interactions between metal gates and dielectrics are observed resulting in nonfunctional devices. MBE LAO film was deposited at room temperature or 200–400 °C in two ways: Using single element targets (La, Al) or a compound target. The LAO/TaN stack deposited with single element targets showed significant Si up diffusion from the substrate to the dielectric and the metal gate electrode. In addition, nitrogen diffusion from the metal gate into the dielectric was detected. The LAO/TaN stack deposited with a compound target showed improved thermal stability. No metal out-diffusion and only very slight Si out diffusion was detected after a 900 °C anneal. LAO capacitors show well-behaved capacitance-voltage and leakage current density-voltage characteristics. These results indicate that the method by which lanthanum aluminate films are deposited strongly influenced their thermal stability. Of all the films examined, the most stable films are deposited by MBE using a compound target.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Structural, electrical, and mechanical properties of nc-TiC/a-SiC nanocomposite thin films

P. Eklund, J. Emmerlich, H. Högberg, O. Wilhelmsson, P. Isberg, J. Birch, P. O. Å. Persson, U. Jansson, and L. Hultman

J. Vac. Sci. Technol. B 23, 2486 (2005); http://dx.doi.org/10.1116/1.2131081 (10 pages) | Cited 22 times

Online Publication Date: 11 November 2005

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We have synthesized Ti–Si–C nanocomposite thin films by dc magnetron sputtering from a Ti3SiC2 compound target in an Ar discharge on Si(100), Al2O3(0001), and Al substrates at temperatures from room temperature to 300 °C. Electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy showed that the films consisted of nanocrystalline (nc-) TiC and amorphous (a-) SiC, with the possible presence of a small amount of noncarbidic C. The growth mode was columnar, yielding a nodular film-surface morphology. Mechanically, the films exhibited a remarkable ductile behavior. Their nanoindentation hardness and E-modulus values were 20 and 290 GPa, respectively. The electrical resistivity was 330 μΩ cm for optimal Ar pressure (4 mTorr) and substrate temperature (300 °C). The resulting nc-TiC/a-SiC films performed well as electrical contact material. These films’ electrical-contact resistance against Ag was remarkably low, 6 μΩ at a contact force of 800 N compared to 3.2 μΩ for Ag against Ag. The chemical stability of the nc-TiC/a-SiC films was excellent, as shown by a Battelle flowing mixed corrosive-gas test, with no N, Cl, or S contaminants entering the bulk of the films.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Lm Deformation, plasticity, and creep
73.61.Jc Amorphous semiconductors; glasses
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
73.40.Cg Contact resistance, contact potential

Ultra small self-organized nitride nanotips

L. W. Ji, T. H. Fang, S. C. Hung, Y. K. Su, S. J. Chang, and R. W. Chuang

J. Vac. Sci. Technol. B 23, 2496 (2005); http://dx.doi.org/10.1116/1.2131083 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2005

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Vertical self-organized nanotips were grown on InGaN film via metal-organic chemical vapor deposition (MOCVD) and thermal annealing. It was found that the typical height of these nanotips is 20 nm with an average width of 1 nm. It was also found that the local density of the vertically grown self-assembled InGaN nanotips could reach 1.6×1013 cm−2. The possible formation mechanism of self-assembled nanotips has been also discussed in this work. Such a small size of vertical nanotips could show strong quantum localization effects and have potential applications in field emission devices, near-field microscopy, and blue photonics.
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68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.67.Hc Quantum dots
81.16.Dn Self-assembly
82.33.Ya Chemistry of MOCVD and other vapor deposition methods

Reactive-ion etching of high-Q and submicron-diameter GaAs/AlAs micropillar cavities

S. Varoutsis, S. Laurent, I. Sagnes, A. Lemaître, L. Ferlazzo, C. Mériadec, G. Patriarche, I. Robert-Philip, and I. Abram

J. Vac. Sci. Technol. B 23, 2499 (2005); http://dx.doi.org/10.1116/1.2131084 (5 pages) | Cited 12 times

Online Publication Date: 11 November 2005

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We present a fabrication process allowing the realization of high-Q and small-diameter micropillar cavities. The fabrication involves molecular beam epitaxy, electron-beam lithography, and reactive ion etching (RIE). The introduction of O2 to the SiCl4 RIE plasma and the dynamic adjustment of its flow rate enable the control of the etched profile throughout the process, through the deposition of silicon oxide on the vertical etched surfaces. The resulting cavities have very smooth, straight, and vertical sidewalls and remain optically and mechanically stable for long periods of time. The optical modes sustained by these cavities exhibit record quality factors in excess of 1200 for pillar diameters close to 400 nm, which underscores the quality of our process.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
85.60.-q Optoelectronic devices
52.77.Bn Etching and cleaning
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography

Design and simulation of ZnO-based light-emitting diode structures

Sang Youn Han, Hyucksoo Yang, D. P. Norton, S. J. Pearton, F. Ren, A. Osinsky, J. W. Dong, B. Hertog, and P. P. Chow

J. Vac. Sci. Technol. B 23, 2504 (2005); http://dx.doi.org/10.1116/1.2131869 (6 pages) | Cited 6 times

Online Publication Date: 11 November 2005

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Two different types of ZnO-based light-emitting diode structures have been examined using a one-dimensional (1D) simulator that accounts for specific features of the hexagonal semiconductors—strong piezoeffects, existence of spontaneous electric polarization, low efficiency of acceptor activation, and high threading dislocation density (normally, ∼ 107–109 cm−2) in the material. A hybrid ZnO/CdZnO/AlGaN/GaN structure grown on sapphire avoids problems in achieving robust p-type doping in ZnO. An all-ZnO approach employs a MgZnO/CdZnO/MgZnO double heterostructure grown on a ZnO substrate. Both structures show a strong sensitivity of emission intensity to doping and layer thicknesses within our simulations.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.05.Ea III-V semiconductors
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.55.Cr III-V semiconductors
85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors
77.65.-j Piezoelectricity and electromechanical effects
77.22.Ej Polarization and depolarization
61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations

Electrical transport of tetragonal boron nanobelts

K. Kirihara, Z. Wang, K. Kawaguchi, Y. Shimizu, T. Sasaki, N. Koshizaki, H. Hyodo, K. Soga, and K. Kimura

J. Vac. Sci. Technol. B 23, 2510 (2005); http://dx.doi.org/10.1116/1.2131870 (4 pages) | Cited 7 times

Online Publication Date: 11 November 2005

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We measured electrical conductances in single crystalline boron nanobelts having α-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method. We obtained ohmic contacts to both pure and Mg-doped nanobelt by metal electrodes of Ni/Au bilayer. From the temperature dependence of electrical conductance, we found that the pure boron nanobelt is a semiconductor. The electrical conductivity of pure boron nanobelt was estimated to be on the order of 10−3 (Ω cm)−1 at room temperature. After Mg vapor diffusion, the electrical conductance increased by a factor of 100 but a transition to metal was not observed.
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73.63.Fg Nanotubes
73.40.Ns Metal-nonmetal contacts
66.30.J- Diffusion of impurities
61.72.up Other materials

Effects of doping type and concentration on precipitation of nanometer arsenic clusters in low-temperature-grown GaAs

W. N. Lee, Y. F. Chen, J. H. Huang, X. J. Guo, and C. T. Kuo

J. Vac. Sci. Technol. B 23, 2514 (2005); http://dx.doi.org/10.1116/1.2131872 (4 pages)

Online Publication Date: 11 November 2005

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In this study, the effects of doping type and concentration on arsenic precipitation in low-temperature-grown GaAs upon postgrowth annealing at 600, 700, and 800 °C were investigated. Three undoped/Si-doped/undoped (i-n-i) regions and three undoped/Be-doped/undoped (i-p-i) regions were grown by low-temperature molecular beam epitaxy. The results show that arsenic precipitation is dependent on doping type and doping concentration. Arsenic depletion was observed in all Be-doped layers for all annealing temperatures. However, a “dual” arsenic precipitation behavior was observed in Si-doped layers: As accumulates in [Si] = 2×1018 cm−3 doped layers, while it depletes in [Si] = 2×1016 and 2×1017 cm−3 doped layers. We attribute this “dual” As precipitation phenomenon in Si-doped layers to the different depletion depths.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
61.72.S- Impurities in crystals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
81.30.Mh Solid-phase precipitation
61.72.Cc Kinetics of defect formation and annealing

Acidic acrylic polymers for nanoimprint lithography on flexible substrates

Wen-chang Liao and Steve Lien-Chung Hsu

J. Vac. Sci. Technol. B 23, 2518 (2005); http://dx.doi.org/10.1116/1.2131874 (4 pages) | Cited 2 times

Online Publication Date: 11 November 2005

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A series of environmental friendly acidic resists were prepared for nanoimprint lithography on flexible plastic substrates. These resists can be easily removed by an aqueous base solution at the final stripping step instead of using an organic solvent or reactive ion etching (RIE), which is used in conventional imprint processes. The resist polymers were prepared via free radical copolymerization of methylmethacrylate (MMA), n-butylacrylate (n-BA) and methacrylic acid (MAA) monomers. For use on flexible plastic substrates, the glass transition temperatures of these polymers were adjusted to a range of 25–41 °C according to the molar ratio of the monomers. The weight average molecular weights (Mw) of these polymers were between 30 000 and 40 000 g/mole measured by GPC. Replications of high-density line and space patterns with resolution of 5 μm and 100 nm were obtained on a flexible indium tin oxide/poly(ethylene terephthalate) (ITO/PET) substrate. The subsequent ITO etching pattern was also achieved.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Ultrathin pore-seal film by plasma enhanced chemical vapor deposition SiCH from tetramethylsilane

Akira Furuya, Katsumi Yoneda, Eiichi Soda, Toru Yoshie, Hiroshi Okamura, Miyoko Shimada, Nobuyuki Ohtsuka, and Shinichi Ogawa

J. Vac. Sci. Technol. B 23, 2522 (2005); http://dx.doi.org/10.1116/1.2132324 (4 pages) | Cited 5 times

Online Publication Date: 11 November 2005

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One important issue for integrating atomic layer deposition (ALD) TaN on a template type porous low-k film is penetration of Ta precursor into the pores. Deposition of a thin film on a patterned sidewall by plasma enhanced chemical vapor deposition (PECVD) is a candidate for pore sealing. We have examined PECVD-SiCH from tetramethylsilane [Si(CH3)4:4MS] as a pore sealant and compared it to PECVD-SiOC from 4MS/CO2 and SiO2 from tetraethoxysilane [Si(OC2H5)4:TEOS]. ALD-TaN had an incubation time on a blanket SiCH, while it did not on a SiCH patterned wafer. The SiCH had the lowest deposition rate and the highest step coverage which enabled deposition of an ultrathin pore-sealing film as thin as 2 nm. Damascene Cu interconnects fabricated by using ALD-TaN barrier metal and the ultrathin SiCH pore-seal demonstrated good electrical characteristics which successfully presented the increase in leakage current due to metal penetration, and it minimized the increase in line resistance by keeping the sealing layer thin.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Rm Porous materials; granular materials
68.55.A- Nucleation and growth
52.77.Dq Plasma-based ion implantation and deposition
61.43.Gt Powders, porous materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Pulse oscillation of self-organized In0.53Ga0.47As quantum wire lasers grown on (775)B InP substrates by molecular beam epitaxy

H. Hino, A. Shigenobu, K. Ohmori, T. Kitada, S. Shimomura, and S. Hiyamizu

J. Vac. Sci. Technol. B 23, 2526 (2005); http://dx.doi.org/10.1116/1.2126670 (4 pages) | Cited 2 times

Online Publication Date: 21 November 2005

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A self-organized In0.53Ga0.47As/(In0.53Ga0.47As)2(In0.52Al0.48As)2 quantum wire (QWR) laser was grown on a (775)B InP substrate by molecular beam epitaxy. Threefold 3.6-nm-thick In0.53Ga0.47As QWR layers were used as an active layer, where lateral confinement potential was induced by a nanometer scale interface corrugation of InGaAs/(InGaAs)2(InAlAs)2 with an amplitude of 7 nm and a period of 65 nm. Photoluminescence was strongly polarized along the wire direction [P ≡ (I‖−I⊥)/(I‖+I⊥) = 0.43–0.54] in the temperature range from 12 to 150 K, indicating their good one dimensionality. A 10 μm×500 μm stripe-contact QWR laser with uncoated cleaved mirrors oscillated with a threshold current density of 5.2 kA/cm2 and a lasing wavelength of 1215 nm at 150 K under pulsed current condition.
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42.55.Px Semiconductor lasers; laser diodes
81.07.Vb Quantum wires
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
78.55.Cr III-V semiconductors

Interfacial reactions in nickel/titanium ohmic contacts to n-type silicon carbide

Jae Hyun Park and Paul H. Holloway

J. Vac. Sci. Technol. B 23, 2530 (2005); http://dx.doi.org/10.1116/1.2126677 (8 pages) | Cited 3 times

Online Publication Date: 21 November 2005

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The complex sequence of reactions and resulting material phases that occur during formation of ohmic contacts using a trilayer titanium/nickel/titanium structure on n-SiC have been studied. The Ti/Ni/Ti contacts on SiC were rectifying in the as-deposited state, but became ohmic upon annealing at 1000 °C for 2 min in a N2 ambient, resulting in a specific contact resistance (ρC) as low as 1×10−4 Ω cm2. X-ray diffraction, Auger electron spectroscopy data and transmission electron microscopy analysis showed that Ni2Si, TiC and graphitic-bound C formed as a result of the annealing. The top Ti layer remained intact as predominantly titanium oxide with minor amounts of TiC. The Ni layer was converted to a double Ni2Si layer containing graphitic C nonuniformly distributed. The bottom Ti layer was converted to a TiC layer separating the two Ni2Si layers, and graphitic C was concentrated in a discontinuous layer near the Ni2Si/SiC interface. The reasons for the formation of this complicated microstructure were discussed.
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73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
61.72.Cc Kinetics of defect formation and annealing
79.20.Fv Electron impact: Auger emission
68.37.Lp Transmission electron microscopy (TEM)

Investigation of surface treatment schemes on n-type GaN and Al0.20Ga0.80N

Deepak Selvanathan, Fitih M. Mohammed, Jeong-Oun Bae, Ilesanmi Adesida, and Katherine H. A. Bogart

J. Vac. Sci. Technol. B 23, 2538 (2005); http://dx.doi.org/10.1116/1.2131078 (7 pages) | Cited 7 times

Online Publication Date: 21 November 2005

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The effects of SiCl4 reactive-ion-etching (RIE) plasma treatment on n-GaN and n-Al0.20Ga0.80N surfaces, and the subsequent cleaning of the surfaces using ammonium hydroxide (NH4OH), hydrochloric acid (HCl), and buffered oxide etch (BOE) solutions, have been investigated using x-ray photoelectron spectroscopy and Auger electron spectroscopy measurements. Of these cleaning schemes, BOE was found to be the most effective treatment to remove oxides from the surfaces of the SiCl4 plasma treated samples. The SiCl4 plasma treatment of GaN and AlGaN resulted in the blueshift of Ga–N (Ga3d) peaks to higher binding energies corresponding to a shift of the Fermi level (EF) toward the conduction band edge at the surface. It has been reported that this type of shift is caused by the creation of N vacancies, which act as n-type dopant [ D. W. Jenkins and J. D. Dow, Phys. Rev. B. 39, 3317 (1989) ; M. E. Lin, Z. F. Fan, Z. Ma, L. H. Allen, and H. Morkoç, Appl. Phys. Lett. 64, 887 (1994) ; A. T. Ping, Q. Chen, J. W. Yang, M. A. Khan, and I. Adesida, J. Electron. Mater. 27, 261 (1998) ] on the surface due to SiCl4 plasma treatment. This corresponds to an increase in n-type dopant density on the surface. Thus, SiCl4 plasma treatment in a RIE system thins the Schottky barrier heights of n-GaN and n-AlGaN and aids in the formation of ohmic contacts on such surfaces.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Fv Electron impact: Auger emission
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Thickness and density evaluation for nanostructured thin films by glancing angle deposition

Cristina Buzea, Kate Kaminska, Gisia Beydaghyan, Tim Brown, Chelsea Elliott, Cory Dean, and Kevin Robbie

J. Vac. Sci. Technol. B 23, 2545 (2005); http://dx.doi.org/10.1116/1.2131079 (8 pages) | Cited 8 times

Online Publication Date: 21 November 2005

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Thickness evaluation is a particular challenge encountered in the fabrication of nanosculptured thin films fabricated by glancing angle deposition (GLAD). In this article, we deduce equations which allow for accurate in situ thickness monitoring of GLAD thin films deposited onto substrates tilted with respect to the direction of incoming vapor. Universal equations are derived for the general case of Gaussian vapor flux distribution, off-axis sensors, variable substrate tilt, and nonunity sticking coefficient. The mathematical description leads to an incidence angle dependence of thickness and density, allowing for quantitative prediction of porosity in samples with different morphologies and thickness calibrations. In addition, variation of sticking probability with the incidence angle creates a nonmonotonic variation of the film thickness and porosity with the substrate tilt. We discuss the implications of the substrate type, sensor type, and source geometry in a precise quantitative determination of the thickness of thin films fabricated on tilted substrates. Our equations can be particularized for the case of films fabricated at normal incidence.
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68.55.-a Thin film structure and morphology
68.60.Wm Other nonelectronic physical properties
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
06.30.Dr Mass and density

Effects of etch barrier densification on step and flash imprint lithography

S. Johnson, R. Burns, E. K. Kim, M. Dickey, G. Schmid, J. Meiring, S. Burns, C. G. Willson, D. Convey, Y. Wei, P. Fejes, K. Gehoski, D. Mancini, K. Nordquist, W. J. Dauksher, et al.

J. Vac. Sci. Technol. B 23, 2553 (2005); http://dx.doi.org/10.1116/1.2102971 (4 pages) | Cited 7 times

Online Publication Date: 29 November 2005

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Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Phase transformations in copper oxide nanowires

Sheng Han, Hong-Ying Chen, Yuh-Bin Chu, and Han C. Shih

J. Vac. Sci. Technol. B 23, 2557 (2005); http://dx.doi.org/10.1116/1.2126672 (4 pages) | Cited 3 times

Online Publication Date: 29 November 2005

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Cu nanowires were electrodeposited into the nanopores of self-ordered aluminum oxide films. CuO and Cu2O nanowires were fabricated by oxidizing Cu nanowires in air. Cu nanowires oxidized at 250 °C transform only to Cu2O (grain size ∼ 21 nm), they transform to a mixture of CuO and Cu2O above 350 °C and finally to CuO with a preferred orientation of CuO (111) at 900 °C.
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64.70.Nd Structural transitions in nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
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Material and electrical analysis of hafnium titania bilayer dielectric metal-oxide-semiconductor field-effect transistors

Se Jong Rhee, Chang Yong Kang, Chang Hwan Choi, Manhong Zhang, and Jack C. Lee

J. Vac. Sci. Technol. B 23, 2561 (2005); http://dx.doi.org/10.1116/1.2126676 (3 pages) | Cited 3 times

Online Publication Date: 30 November 2005

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An approach of fabricating laminated titanium oxide on hafnium oxide bilayer dielectric has been developed for future high-performance device applications. The dielectric layers showed negligible intermixing and no silicide formation with silicon substrate. X-ray diffraction analysis demonstrated superior thermal stability (>950 °C) of the hafnium titania bilayer dielectric. With the same total physical thickness of dielectric, a thicker titanium oxide layer resulted in improved electrical characteristics. It has been found that the hafnium titania bilayer dielectric metal-oxide-semiconductor field-effect transistor showed not only improved output current and transconductance, but also increased electron and hole mobility compared to hafnium binary oxide device.
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85.30.Tv Field effect devices
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
72.20.Fr Low-field transport and mobility; piezoresistance
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Electrochemical fabrication of cobalt and nickel tips for scanning tunneling microscopy

Cristiano Albonetti, Massimiliano Cavallini, Massimiliano Massi, Jean François Moulin, and Fabio Biscarini

J. Vac. Sci. Technol. B 23, 2564 (2005); http://dx.doi.org/10.1116/1.2131873 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2005

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Scanning tunneling microscopy (STM) is a powerful technique to map the distribution of the density of electronics states of conductive surfaces with angstrom (Å) resolution. STM requires sharp conductive tips in order to operate in ambient conditions, which are stable with respect to oxidation. We describe a procedure to obtain high quality tips from wires of different materials such as Co and Ni. We discuss in detail the electrochemical process employed in the fabrication of the tips and assess the shape of the tips by optical microscopy and scanning electron microscopy (SEM). These tips yield high-resolution STM images even after a few weeks of exposure to air.
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07.79.Cz Scanning tunneling microscopes
82.45.Aa Electrochemical synthesis
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back to top Plenary Talks

Modeling and simulation for nanometrics

Andrew R. Neureuther and Daniel Ceperley

J. Vac. Sci. Technol. B 23, 2578 (2005); http://dx.doi.org/10.1116/1.2062447 (6 pages) | Cited 1 time

Online Publication Date: 30 November 2005

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Nanoscale phenomena and especially surface plasmon-based optical devices are playing important roles in historical and emerging applications of photography, instrumentation, imaging, and signal processing. Simulation of these devices is synergistic with invention, and commercial computer-aided design infrastructure will eventually follow to cope with design and manufacturing. Devices based on source-free solutions to Maxwell’s equations, such as plasmons and guided waves, are emphasized. They include the Daguerrotype and plasmon scattering from topographical features. A more general survey of the applications of simulation to optical nanodevices is also included. For finite-difference time domain using up to 250 million nodes, the major computational challenges are associated with the nm-level detail of large distributed structures, the small real part of the refractive index, and the necessity to accurately compute phases.
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85.35.-p Nanoelectronic devices

History of extreme ultraviolet lithography

Hiroo Kinoshita

J. Vac. Sci. Technol. B 23, 2584 (2005); http://dx.doi.org/10.1116/1.2127950 (5 pages) | Cited 4 times

Online Publication Date: 30 November 2005

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Extreme ultraviolet lithography (EUVL) technology was proposed and progressed on both hemispheres in the latter part of the 1980s, independently. Although this technology is a design using a catoptric system instead of refraction lens and the accuracy of subnanometer is demanded for all component engineering, the research and development of Japan and the United States has led to significant breakthroughs in processing and measurement technology over the past 20 years. EUVL is now the most promising next-generation technology for large scale integration fabrication. This article discusses the beginnings of EUVL, what advances are needed, and future prospects.
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85.40.Hp Lithography, masks and pattern transfer
back to top Modeling and Simulation

Electron-electron interaction induced beam displacement in a multiple electron beam system

Ming L. Yu, Steven T. Coyle, William DeVore, and Bassam Shamoun

J. Vac. Sci. Technol. B 23, 2589 (2005); http://dx.doi.org/10.1116/1.2101788 (7 pages) | Cited 3 times

Online Publication Date: 30 November 2005

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We have studied electron-electron (e-e) interaction induced beam displacement in multiple electron beam systems both experimentally and using trajectory simulation. A prototype 32-beam lithography system was used to record the beam displacements on chrome mask plates and the latter were directly measured by electron microscopy. Both experimental data and simulation results of demagnifying columns were consistent with a demagnification of the electron beam array with increasing current. While the simulation matched qualitatively the experimental data well, it predicted a smaller effect than measured. The overall demagnification was underestimated by 20%–30%. In an attempt to understand the underlying physical reason, we used a phenomenological model for the e-e induced beam displacement to fit the acquired data. The analysis suggested that the trajectory simulation underestimated the defocusing lens effect of the interacting electrons by about 1.5. The parametric expression derived from this model may be used to correct for global space charge effects during multi-electron beam lithography.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
68.37.-d Microscopy of surfaces, interfaces, and thin films

Full wafer simulation of immersion fluid heating

M. El-Morsi, G. Nellis, S. Schuetter, C. Van Peski, and A. Grenville

J. Vac. Sci. Technol. B 23, 2596 (2005); http://dx.doi.org/10.1116/1.2091091 (5 pages) | Cited 6 times

Online Publication Date: 30 November 2005

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In immersion lithography, fluid is introduced into the region between the lens and wafer. The benefit of the immersion fluid is that it has an index of refraction greater than air, which leads to a higher numerical aperture and improved depth of focus. Since the liquid becomes an optical element in the imaging system, it must maintain a uniform optical quality. However, the liquid’s index of refraction can depend on its temperature, and the temperature of the fluid will rise due to the exposure energy. This article describes a detailed two-dimensional computational fluid dynamics model of the hydrodynamic and thermal aspects of fluid flow. The model focuses on the successive scanning processes that occur as multiple chips are exposed on a wafer and accounts for the resulting oscillatory wafer motion and the thermal loads related to absorption of the incident energy in the fluid, indirect heating of the fluid due to its contact with the wafer as well as viscous dissipation. The global storage of energy in the fluid and the wafer as multiple chips are exposed is considered. The effect of the wafer acceleration, lens-to-wafer spacing, and the thermo-optic coefficient of the immersion fluid are studied parametrically and the impact of these quantities on the temperature distribution is described.
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85.40.Hp Lithography, masks and pattern transfer

Charting the future (and remembering the past) of optical lithography simulation

Chris A. Mack

J. Vac. Sci. Technol. B 23, 2601 (2005); http://dx.doi.org/10.1116/1.2130354 (6 pages)

Online Publication Date: 30 November 2005

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Optical lithography modeling began in the early 1970s and represented the first serious attempt to describe lithography not as an art, but as a science. Thirty years later, optical lithography continues to make dramatic advances that enable the profitable continuation of Moore’s Law. Most if not all of these advances would not be possible without the use of lithography simulators. This article will review the history of lithography simulation, describing a few of the milestone events and important lithographic advances that simulation enabled. This historical review will end with a characterization of the current state of lithography modeling and its important applications in chip design, process development, and manufacturing today. Finally, a prediction of future advances in simulation capabilities will be made as well as how these advances will help to move the industry forward.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling
01.65.+g History of science
back to top Optical Lithography

Dynamic alignment control for fluid-immersion lithographies using interferometric-spatial-phase imaging

Euclid E. Moon, Mark K. Mondol, Patrick N. Everett, and Henry I. Smith

J. Vac. Sci. Technol. B 23, 2607 (2005); http://dx.doi.org/10.1116/1.2101725 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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We demonstrate the application of a high-sensitivity alignment method called interferometric-spatial-phase imaging (ISPI) to a nanometer-level overlay in fluid-immersion lithography, using step-and-flash imprint lithography as the test vehicle. As a stringent test we used alignment marks that consist of pure phase gratings in a fused silica template, immersed in a fluid of similar refractive index, resulting in a low-contrast alignment signal. Feedback control of alignment is demonstrated with mean = 0.0 nm and σ = 0.1 nm using an immersed template. Overlay results, with UV-exposed imprint fluid, were limited to ∼ 4 nm, due to a mechanical disturbance. Because ISPI enables continuous monitoring of the alignment signal, we were able to identify the origin of the mechanical disturbance and can eliminate it in future experiments. In addition, we demonstrate the ability to actively reduce misalignment during the progression of crosslinking in the imprint fluid.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Control of the receding meniscus in immersion lithography

H. Burnett, T. Shedd, G. Nellis, M. El-Morsi, R. Engelstad, S. Garoff, and K. Varanasi

J. Vac. Sci. Technol. B 23, 2611 (2005); http://dx.doi.org/10.1116/1.2090968 (6 pages) | Cited 7 times

Online Publication Date: 1 December 2005

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The implementation of immersion lithography requires a sophisticated fluid management system. The design of the fluid management system must simultaneously consider liquid heating, viscous shear, normal forces, air entrainment, and the control of the liquid/air interfaces. In particular, it is becoming clear that the behavior of the receding air/water interface is critical and must be carefully controlled in order to prevent the deposition of residual liquid due to film pulling or the interface instability referred to as meniscus overflow. This paper discusses these failure mechanisms that are associated with the receding meniscus and that have been experimentally observed. In addition, a simple yet physics-based engineering model of the receding meniscus failure is presented and the results of the model are compared to experimental data.
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47.55.D- Drops and bubbles
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.20.−k
68.35.Ja Surface and interface dynamics and vibrations

Direct patterning of spin-on glass with 157 nm lithography: Application to nanoscale crystal growth

T. M. Bloomstein, P. W. Juodawlkis, R. B. Swint, S. G. Cann, S. J. Deneault, N. N. Efremow, D. E. Hardy, M. F. Marchant, A. Napoleone, D. C. Oakley, and M. Rothschild

J. Vac. Sci. Technol. B 23, 2617 (2005); http://dx.doi.org/10.1116/1.2101692 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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Selective area homoepitaxial growth of InP in 50 nm scale dense features has been demonstrated using hydrogen silsesquioxane (HSQ) as the growth mask. The HSQ growth mask was patterned lithographically using high resolution interference lithography at 157 nm. Lithographic process conditions were optimized, including postapplication bake temperature, developer normality, and oxygen levels during exposure.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.05.Ea III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Hybrid exposure strategy: Combining e-beam direct writing with optical lithography for magnetic recording heads

XiaoMin Yang

J. Vac. Sci. Technol. B 23, 2624 (2005); http://dx.doi.org/10.1116/1.2110340 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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Hybrid exposure strategies have been implemented with commercially available chemically amplified resists for the fabrication of magnetic recording heads. This approach relies on splitting the pattern into high-resolution and low-resolution components at the same resist level. Two critical features of the thin-film head (TFH) device (write top pole and read sensor widths) are defined by e-beam direct writing for the high-resolution patterning, and all other, relatively large features, are patterned with optical lithography for high throughput. In this article we will present the results from the fabrication of sub-50 nm magnetic write and read components with this hybrid exposure process. Key lessons from many aspects of the process development effort will be discussed in relation to TFH fabrication, including dual sensitive resist selection, exposure sequence, postexposure delay effect, e-beam process challenges, and overlay alignment issue. We demonstrate the capability of printing top pole structures with pole widths of sub-40 nm in a 0.35-μm-thick resist film (aspect ratio>8:1), and electroplated top pole structures of 40 nm with CoFe.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials

Use of optical defocus components to investigate and improve pattern spatial frequency characteristics for more robust layouts

Lawrence S. Melvin, James P. Shiely, and Qiliang Yan

J. Vac. Sci. Technol. B 23, 2631 (2005); http://dx.doi.org/10.1116/1.2062687 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2005

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As semiconductor manufacturing moves to smaller geometries, the existing methodologies for verifying the manufacturability of a design are increasingly cumbersome. Current practice is to use geometric “design rules”—such as minimum spacing and width constraints—to identify design configurations that are not manufacturable or likely to reduce yield. One manufacturing property that is particularly difficult to capture accurately with geometric rules is the robustness of the layout configuration with respect to variation through the lithographic process window. The nonlinear characteristics of optical partial coherence effects, particularly strong in modern exposure systems with off-axis illumination, are currently incorporated into the design rules through an exhaustive empirical process. The resulting design rules can be overly conservative to insure complete problem pattern capture, and this may result in unnecessary restrictions on the design that reduce the layout density or interfere with circuit performance. In this article a process model that has been designed to identify process sensitive layout configurations is presented. The model is a spatial filter constructed to select the diffraction components that are most sensitive to focus variation. This defocus model then may be applied to a layout pattern to find features that suffer with lithography focus variation. In addition, the technique may be employed once the optical components of a manufacturing process have been developed. Current results show a good correlation between patterns highlighted using the defocus filter and patterns which will be sensitive to process variations during simulated manufacturing. It is believed that this methodology integrated into physical verification techniques will help to identify yield-limiting layout configurations.
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85.40.Hp Lithography, masks and pattern transfer

Deep subwavelength nanolithography using localized surface plasmon modes on planar silver mask

W. Srituravanich, S. Durant, H. Lee, C. Sun, and X. Zhang

J. Vac. Sci. Technol. B 23, 2636 (2005); http://dx.doi.org/10.1116/1.2091088 (4 pages) | Cited 21 times

Online Publication Date: 1 December 2005

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The development of a near-field optical lithography is presented in this paper. By accessing short modal wavelengths of localized surface plasmon modes on a planar metallic mask, the resolution can be significantly increased while using conventional UV light source. Taking into account the real material properties, numerical studies indicate that the ultimate lithographic resolution at 20 nm is achievable through a silver mask by using 365 nm wavelength light. The surface quality of the silver mask is improved by adding an adhesion layer of titanium during the mask fabrication. Using a two-dimensional hole array silver mask, we experimentally demonstrated nanolithography with half-pitch resolution down to 60 nm, far beyond the resolution limit of conventional lithography using I-line (365 nm) wavelength.
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85.40.Hp Lithography, masks and pattern transfer
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Doppler writing and linewidth control for scanning beam interference lithography

Juan C. Montoya, Chih-Hao Chang, Ralf K. Heilmann, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 23, 2640 (2005); http://dx.doi.org/10.1116/1.2127938 (6 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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Scanning beam interference lithography (SBIL) is a technique which is used to create large-area periodic patterns with high phase accuracy. This is accomplished by combining interference lithography and an X-Y scanning stage. We previously reported parallel scan mode in which the stage scans in a direction parallel to the interference fringes. Here we present a method called Doppler scanning. In this mode, the stage is scanned perpendicular to the interference fringes. In order to obtain high-contrast latent gratings in the exposed photoresist, several parameters must be controlled. These parameters include vibration, fringe period error, time delay (for Doppler writing), dose, beam overlap, and polarization. In this article we present results of how the time delay, fringe period error, and exposure dose effect the contrast and linewidth of our latent grating images. Furthermore, SBIL has a unique ability to read gratings in a metrology mode configuration. This article also describes how Doppler metrology mode allows us to measure the time delay of our system.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography

Screening layouts for high-numerical aperture and polarization effects using pattern matching

Gregory R. McIntyre, Juliet Holwill, Andrew Neureuther, Luigi Capodieci, Yi Zou, Harry Levinson, and Jongwook Kye

J. Vac. Sci. Technol. B 23, 2646 (2005); http://dx.doi.org/10.1116/1.2132333 (7 pages) | Cited 3 times

Online Publication Date: 1 December 2005

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A pattern matching method for quickly estimating the extent to which high-NA and polarization vector effects reduce image quality in projection printing is derived and evaluated for prototypical layout patterns. The angular rotation of the in-incidence plane TM electric field component produces two unwanted effects. It reduces the collinear addition of electric fields at the location of the peak image intensity and, more importantly, it also introduces an electric field component perpendicular to the image plane that acts like stray light. While these imaging effects can be simulated rigorously, the challenge is to quickly screen an entire layout to identify the small subset of regions that must be analyzed more carefully. The approach developed mathematically and evaluated in this paper consists of finding a set of local theoretical patterns having the maximum lateral impact at a reference point. Pattern matching is then used to find areas in a layout that resemble these maximum lateral test functions by scanning them over the entire chip layout. Vulnerability scores, representing linear sensitivity to either high-NA effects or to perturbations of illumination polarization state, are determined for each location from a weighted combination of match factors (the degree of similarity to each pattern). These effects are important as intensity changes of over 40% and 10% can occur with NA and polarization, respectively, even in simple layouts.
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85.40.Hp Lithography, masks and pattern transfer

Understanding the impact of source displacement error on sub-90 nm patterns using a fresnel zone plate

Jangho Shin, Chan Hwang, SukJoo Lee, Sang-Gyun Woo, Han-Ku Cho, and Joo-Tae Moon

J. Vac. Sci. Technol. B 23, 2653 (2005); http://dx.doi.org/10.1116/1.2121733 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2005

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Illumination source radiance distribution has a significant impact on vertical-horizontal bias and critical dimension (CD) variation on production wafers. In this article, the impact of source displacement error (SDE) on sub-90 nm patterning is studied. A Fresnel zone plate (FZP) is adopted as a metrology to quantify the amount of SDE. Experimental data show that some of pupil-fills may have more than 50 mrad of SDE and it could cause a serious pattern shift and/or CD asymmetry. A detailed description of FZP design specifications and application results are presented. Finally, SDE tolerance limits to print sub-90 nm features are discussed.
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81.16.Rf Micro- and nanoscale pattern formation
06.20.Dk Measurement and error theory

Immersion zone-plate-array lithography

David Chao, Amil Patel, Tymon Barwicz, Henry I. Smith, and Rajesh Menon

J. Vac. Sci. Technol. B 23, 2657 (2005); http://dx.doi.org/10.1116/1.2127942 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2005

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An immersion scheme is used to improve resolution, exposure latitude, and depth-of-focus in zone-plate-array lithography (ZPAL). We believe this is the first implementation of an immersion scheme in a maskless lithography system. Replacing air with de-ionized water as the medium between the zone-plate array and the substrate effectively increases the system’s numerical aperture and consequently, enhances its patterning capabilities. The design and fabrication process of an immersion zone plate is described. Its behavior is then characterized through the experimental reconstruction of its point-spread function, and compared to the theoretical model. A wide variety of patterns were printed, demonstrating the improved lithographic performance of immersion ZPAL.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
42.79.Ci Filters, zone plates, and polarizers
42.30.Lr Modulation and optical transfer functions

Pumped quantum systems: Immersion fluids of the future?

Vikas Anant, Magnus Rådmark, Ayman F. Abouraddy, Thomas C. Killian, and Karl K. Berggren

J. Vac. Sci. Technol. B 23, 2662 (2005); http://dx.doi.org/10.1116/1.2121732 (6 pages)

Online Publication Date: 1 December 2005

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Quantum optical techniques may yield immersion fluids with high indices of refraction without absorption. We describe one such technique in which a probe field experiences a large index of refraction with amplification rather than absorption, and examine its practicality for an immersion lithography application. Enhanced index can be observed in a three-level system with a tunable near-resonant coherent probe and incoherent pump field that inverts the population of the probe transition. This observation contradicts the common belief that large indices of refraction are impossible without absorption; however, it is well in accord with existing electromagnetic theory and practice. Calculations show that a refractive index ⪢2 is possible with practical experimental parameters. A scheme with an incoherent mixture of pumped and unpumped atoms is also examined, and is seen to have a lower refractive index ( ∼ 2) accompanied neither by gain nor loss.
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42.50.-p Quantum optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Hyper high numerical aperature achromatic interferometer for immersion lithography at 193 nm

A. L. Charley, A. Lagrange, O. Lartigue, J. Simon, P. Thony, and P. Schiavone

J. Vac. Sci. Technol. B 23, 2668 (2005); http://dx.doi.org/10.1116/1.2135295 (7 pages) | Cited 4 times

Online Publication Date: 1 December 2005

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An apparatus for immersion interferometric lithography is described here where the interfering beams are created by illuminating a first diffraction grating followed by a second diffraction grating recombining the diffracted beams onto the photoresist plane. The main advantage of this system is to be achromatic: thus it is possible to use a basic commercial ArF excimer laser as the exposure source. We present here the calculations made to evaluate the different parameters that can influence the depth of focus in the immersion configuration. As the setup is mainly based on the two diffraction gratings, it matters to properly design it. The purpose of this article is to show the optimization made on the diffraction gratings in taking into account their fabrication process since they are fabricated using the capabilities of the silicon line available in our laboratory. On one hand, calculations have been done to determine the second grating period as a function of the first grating period and the “immersion numerical aperature.” By simply adding a fluid to a “dry” system, we will indeed be able to improve the depth of focus but not the resolution. In playing with the diffraction grating periods, we are able to benefit from the introduction of the immersion fluid. We have performed simulations in order to optimize the grating diffraction efficiency as a function of the etch depth and the fractional linewidth. Finally, we report on the results obtained with the achromatic immersion interferometer. The apparatus was used with a 193 nm GAM excimer laser to print resist patterns having a period of 100 nm with excellent contrast.
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07.60.Ly Interferometers
85.40.Hp Lithography, masks and pattern transfer
42.79.Dj Gratings

Propagating modes in subwavelength cylindrical holes

Peter B. Catrysse, Hocheol Shin, and Shanhui Fan

J. Vac. Sci. Technol. B 23, 2675 (2005); http://dx.doi.org/10.1116/1.2130344 (4 pages) | Cited 11 times

Online Publication Date: 1 December 2005

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We analyze subwavelength cylindrical holes in an optically thick metallic film with the metal described by a plasmonic model. We emphasize that such holes always support propagating modes near the surface plasmon frequency, regardless of how small the holes are. Based on this analysis, we design both single holes and hole arrays in which propagating modes play a dominant role in the transport properties of incident light. These structures exhibit a region of operation that to the best of our knowledge has not been probed yet experimentally, while featuring a high packing density and diffraction-less behavior.
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78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.70.-a Optical materials

Full field analysis of lithography performance for ArF immersion lithography

Yanqiu Li and Guosheng Huang

J. Vac. Sci. Technol. B 23, 2679 (2005); http://dx.doi.org/10.1116/1.2101790 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2005

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Full field analysis of pattern displacement caused by lens aberrations for ArF immersion lithography is presented for the critical dimension (CD) of the 65 nm node. Pattern displacement (PD) is the most critical issue for lithography performance if the CD uniformity is constrained within ΔCD<±10% CD and the depth of focus is larger than 0.4 μm. In-house MicroCruiser software was developed and generated mass groups of 36 Zernike coefficients with certain root mean square of wave-front error (rms WFE) and peak-to-valley value of WFE in order to study the cross talk between different Zernike coefficients. MicroCruiser communicated with PROLITH 8.0 commercial software and processed mass data automatically. The mass results of lithography performance were completed under different conditions of lens aberrations, mask types, and exposure-tool settings at each field point. The results show that with the same rms WFE, the PD will be larger if an alternate phase-shifting mask and conventional illumination are employed as compared the PD if a binary mask and annular illumination are used. For the impact of aberrations on imaging performance, the cross talk between different Zernike coefficients is more essential than a mere rms WFE.
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85.40.Hp Lithography, masks and pattern transfer

Simulation of air bubble scattering effects in 193 nm immersion interferometric lithography

C. H. Lin and L. A. Wang

J. Vac. Sci. Technol. B 23, 2684 (2005); http://dx.doi.org/10.1116/1.2134716 (10 pages) | Cited 2 times

Online Publication Date: 1 December 2005

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In 193 nm immersion lithography, the presence of air bubbles in water poses a serious concern to the resist image formation. In this study, air bubble scattering effects were characterized by the Mie theory and the finite-difference time-domain (FDTD) method. The influence range of bubbles both in forward and lateral directions with respect to their sizes was analyzed. It is predicted that as bubble size exceeds 90 nm in diameter, light scattering becomes significant. In the FDTD simulation, the effects of scattered waves in two- and three-beam interferometric lithography were simulated to mimic the actual imaging formation in an immersion scanner. It is found that the more beams are involved in the image formation, the more scattered waves interfere with the image forming waves, and then degrade the final image. Finally, the effect of a moving bubble was also simulated. The phenomenon of image distortion in the presence of bubbles was simulated by employing the three-dimensional FDTD method.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication of enclosed nanochannels using silica nanoparticles

Deying Xia and S. R. J. Brueck

J. Vac. Sci. Technol. B 23, 2694 (2005); http://dx.doi.org/10.1116/1.2130358 (6 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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We report a simple and inexpensive approach to the fabrication of enclosed nanoscale channels composed of silica nanoparticles on planar Si surfaces using interferometric lithography to define the long-range pattern in a photoresist film followed by spin-coating self-assembly of colloidal silica nanoparticles and high-temperature calcination to remove the photoresist leaving open nanochannels. Channel structures with channel width and height ranging from ∼ 100 nm to over 1 μm were formed over large areas with different particle sizes and channel profiles. The dimensional scale of these ordered arrays of enclosed channels can be easily controlled through the parameters in the photoresist patterning and the spin-coating steps. Complex, multilayer structures have been generated using this approach as well. This process opens a route to fabricating ordered enclosed nanochannels with potential uses in photonics, molecular/biological sensors, biological separations and catalysis.
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81.07.Bc Nanocrystalline materials
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Large-area, infrared nanophotonic materials fabricated using interferometric lithography

Wenjun Fan, Shuang Zhang, K. J. Malloy, and S. R. J. Brueck

J. Vac. Sci. Technol. B 23, 2700 (2005); http://dx.doi.org/10.1116/1.2132334 (5 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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In this paper, we discuss the characterization and fabrication of two nanophotonic materials for the infrared region by using IL—realizing a negative refractive index material and enhancing transmission through annular metallic coaxial aperture arrays.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Achromatic spatial frequency multiplication: A method for production of nanometer-scale periodic structures

Harun H. Solak and Yasin Ekinci

J. Vac. Sci. Technol. B 23, 2705 (2005); http://dx.doi.org/10.1116/1.2121735 (6 pages) | Cited 8 times

Online Publication Date: 1 December 2005

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Fabrication of periodic structures with resolution below 100 nm is required in many emerging applications such as subwavelength optical components, self-assembly templates, or patterned magnetic media. The achromatic spatial frequency multiplication technique that we have developed uses wideband illumination and self-imaging property (Talbot effect) of gratings to create periodic structures. The depth of field is practically unlimited, unlike the Talbot images obtained with monochromatic illumination. The technique requires limited spatial coherence making it suitable for use with sources other than lasers or synchrotrons which are normally used in interference lithography. We demonstrated the feasibility of the method using simulations and exposures in the extreme ultraviolet (EUV) region. One- and two-dimensional patterns with 50 nm feature sizes were obtained. The technique is especially suitable for use with EUV light where the newly developed sources (laser or discharge produced plasma) have a rather wide bandwidth and limited spatial coherence. The technique is extendible to the production of much higher-resolution structures with the fundamental limit for the pattern period being equal to one-half of the wavelength.
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81.16.Nd Micro- and nanolithography
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.79.Dj Gratings
back to top Resist Science and Technology

Spectral analysis of line-edge roughness in polyphenol EB-resists and its impact on transistor performance

Atsuko Yamaguchi, Hiroshi Fukuda, Tadashi Arai, Jiro Yamamoto, Taku Hirayama, Daiju Shiono, Hideo Hada, and Junichi Onodera

J. Vac. Sci. Technol. B 23, 2711 (2005); http://dx.doi.org/10.1116/1.2110318 (5 pages) | Cited 14 times

Online Publication Date: 1 December 2005

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Resists using polyphenol resin are introduced to reduce line-edge roughness (LER), and the spatial frequency characteristics of LER are evaluated. It is found that the long-period components of LER are suppressed in our low molecular-weight polyphenol resists. Device simulation using the measured LER shows that our polyphenol-based resist can drastically reduce the number of low-threshold-voltage (Vth) transistors compared with a conventional resist due to reduced long-period LER. Because LER impact is more serious as the transistor width shrinks, our results suggest that the use of the polyphenol-type resist will be more effective in improving device performance in future lithography process. In addition, it is shown that spectral analysis is a powerful tool for LER evaluation, especially from the viewpoint of device performance estimation.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Proton and anion distribution and line edge roughness of chemically amplified electron beam resist

Takahiro Kozawa, Hiroki Yamamoto, Akinori Saeki, and Seiichi Tagawa

J. Vac. Sci. Technol. B 23, 2716 (2005); http://dx.doi.org/10.1116/1.2131875 (5 pages) | Cited 31 times

Online Publication Date: 1 December 2005

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Nanoscale resist topography such as line edge roughness (LER) or line width roughness (LWR) is the most serious concern in sub-100 nm fabrication. Many factors have been reported to affect LER. However, the cause of LER is still unclear. We calculated proton and anion distribution of chemically amplified electron beam resists in order to make clear the cause of LER. Counter anion distribution is significantly different from proton distribution. Counter anions are inhomogeneously distributed outside a relatively smooth edge of proton distribution. This is caused by the fact that acid generators can react with low-energy ( ∼ 0 eV) electrons. The inhomodeneous distribution of counter anions outside proton distribution is considered to contribute to LER formation in chemically amplified resists for post optical lithographies.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Static and dynamic contact angles of water on photoresist

H. Burnett, T. Shedd, G. Nellis, and C. Van Peski

J. Vac. Sci. Technol. B 23, 2721 (2005); http://dx.doi.org/10.1116/1.2131878 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2005

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Fluid management issues in an immersion lithography system include the retention of the liquid (i.e., prevention of residual liquid on the wafer) and the possible entrainment of gas bubbles within the immersion fluid. Three key parameters strongly influence the control of fluid within the lens gap: the static liquid/resist contact angle, the contact angle hysteresis, and the dynamic contact angle characteristics. This article presents a comprehensive set of data for these parameters on silicon wafers coated with six different photoresists and describes the experimental apparatus and data reduction techniques used to collect the data. Measurements for six candidate photoresists, one with a top-coat, indicate that air entrainment due to contact line motion is highly unlikely for typical immersion lithography systems. However, significant contact angle hysteresis does exist that may lead to meniscus failure and to the deposition of droplets at low to moderate wafer velocities. In addition, the receding dynamic contact angle can approach zero on some surfaces, leading to liquid film deposition.
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47.55.D- Drops and bubbles
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.20.−k
68.35.Ja Surface and interface dynamics and vibrations

Study on acid generation from polymer

Hiroki Yamamoto, Takahiro Kozawa, Atsuro Nakano, Kazumasa Okamoto, Seiichi Tagawa, Tomoyuki Ando, Mitsuru Sato, and Hiroji Komano

J. Vac. Sci. Technol. B 23, 2728 (2005); http://dx.doi.org/10.1116/1.2121730 (5 pages) | Cited 12 times

Online Publication Date: 1 December 2005

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In the fabrication beyond the 32 nm node, the uniform distribution of acid generators in a resist matrix is a serious concern. The incorporation of acid generators to polymers via covalent bonds has attracted much attention in order to overcome the compatibility problem of acid generators with polymers. We reported the reaction mechanism of acid generation in typical chemically amplified resists for ionizing radiation, such as electron beam and extreme ultraviolet. The simplest way to induce the same reactions in a single-component resist is the halogenation of polymers. We carried out a case study on the acid generation from polymers using brominated poly(4-hyroxystyrene) (Br-PHS). Br-PHS without an acid generator produced hydrogen bromide with the same amount as acid yield of PHS with 1.2 mol % (4.1 wt %) triphenylsulfonium-triflate. It was confirmed that Br-PHS with hexamethoxy methyl melamine worked as a chemically amplified resist without any acid generators. From the comparison among the acid yields of Br-PHS, PHS, poly(4-bromostyrene) and polystyrene, we concluded that the efficient acid generation from polymers requires a high reactivity with electrons, a high dissociation efficiency of counter anions, and an effective proton source, such as hydroxyl group.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Full three-dimensional characterization of 25 nm lines for chemically amplified resist simulation

S. Landis, S. Pauliac, J. Foucher, J. Thiault, and F. de Crecy

J. Vac. Sci. Technol. B 23, 2733 (2005); http://dx.doi.org/10.1116/1.2132327 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2005

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Low molecular weight negative tone chemically amplified resist has been exposed with 100 kV electron beam writer with a postexposure bake temperature varying between 85 and 100 °C. Isolated lines, with feature size ranging from 20 up to 100 nm, have been characterized with scanning electron microscopy and critical dimension atomic force microscopy. A simple kinetic reaction law and lateral acid diffusion into the resist layer were taken into account for the cross-linking reaction simulation. Top view and full three-dimensional measurements of resist feature have been fitted with an analytical expression. A cost function was introduced to extract the reaction order (m) and the acid diffusion coefficient (D) of the second Fick’s law. Whatever the process temperature used, a constant value for m(m = 2.6) was found, and D was found to vary from 2 to 45 nm2/s for a postexposure bake temperature of 85 and 100 °C, respectively. Depending on the metrology technology used for resist characterization resist parameter extraction may be significantly impacted, especially for very narrow resist line simulation.
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61.80.Fe Electron and positron radiation effects
82.20.-w Chemical kinetics and dynamics
66.30.-h Diffusion in solids
85.40.Hp Lithography, masks and pattern transfer
back to top Maskless Lithography

Effects of through-focus symmetry in maskless lithography using micromirror arrays

J.-S. Wang, S. Hafeman, A. R. Neureuther, and O. Solgaard

J. Vac. Sci. Technol. B 23, 2738 (2005); http://dx.doi.org/10.1116/1.2062407 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2005

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In this article we model and characterize the effects of the through-focus asymmetry induced by pixels with phases other than 0 and π in micromirror arrays for maskless lithography. Analytic models for several mirror configurations are provided and shown to result in small deviations (±1.5%) from simulation results. These models, together with full simulations, are used to compare multiple-tilt and multiple-piston mirrors. The results show that for comparable multiple-tilt and multiple-piston mirrors, the piston mirrors have better modulation characteristics. A test of off-grid printing is performed, suggesting that the four-piston mirror is the best configuration for maskless lithography.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.79.Bh Lenses, prisms and mirrors

Hybrid optical maskless lithography: Scaling beyond the 45 nm node

M. Fritze, T. M. Bloomstein, B. Tyrrell, T. H. Fedynyshyn, N. N. Efremow, D. E. Hardy, S. Cann, D. Lennon, S. Spector, M. Rothschild, and P. Brooker

J. Vac. Sci. Technol. B 23, 2743 (2005); http://dx.doi.org/10.1116/1.2062327 (6 pages) | Cited 7 times

Online Publication Date: 1 December 2005

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Optical lithography at 193 nm with resolution enhancements and immersion is widely expected to meet the needs of the 45 nm node. Beyond this, at 32 nm and below, the solution is not as clear. In this article we present simulation results and experimental demonstrations of an all-optical approach capable of high-throughput 32 nm lithography (hybrid optical maskless lithography). In this method high-resolution dense gratings are defined in a first exposure using maskless interference lithography. A second “trim” exposure, using conventional projection lithography, customizes these gratings into useful patterns. Our simulations indicate that 32 nm node patterning can be achieved using trim tools and masks of significantly lower resolution. We also present experimental feasibility results using 157 nm “dry” interference in combination with projection 248 nm or e-beam trim exposures. The technological requirements and extendibility of such a method beyond the 32 nm node are also examined.
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81.16.Nd Micro- and nanolithography
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
back to top Electron Beam Lithography and Imaging

Dynamic chromatic aberration correction in low energy electron microscopes

Anjam Khursheed

J. Vac. Sci. Technol. B 23, 2749 (2005); http://dx.doi.org/10.1116/1.2062432 (5 pages)

Online Publication Date: 2 December 2005

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This paper presents a method of dynamically correcting for the chromatic aberration in pulsed gun low energy electron microscope systems. The proposal is based upon the use of a drift tube in combination with electron lenses whose focal strengths can be rapidly modulated. Simulation results that use direct ray tracing of electrons are presented for specific drift tube/correction lens combinations.
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41.85.Gy Chromatic and geometrical aberrations
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.Ne Electrostatic lenses, septa

Performances by the electron optical system of low energy electron beam proximity projection lithography tool with a large scanning field

Haruo Kasahara, Tsutomu Shishido, Norihiko Samoto, and Nobuo Shimazu

J. Vac. Sci. Technol. B 23, 2754 (2005); http://dx.doi.org/10.1116/1.2062435 (4 pages) | Cited 1 time

Online Publication Date: 2 December 2005

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An electron optical system has been developed for a low energy electron beam proximity projection lithography tool that is capable of scanning a field of 40 mm square with a beam current up to 20 μA. By using a beam current of 18 μA the system has successfully resolved a dense 46 nm hole pattern with 90 nm pitch near one corner of the field. This article introduces a double-pinhole technique to monitor and measure the telecentricity of the electron beam (or e-beam) of such a system. Other related areas covered in the article are the simulations of space charge effect and of deflection aberration: also discussed here is the linearity of the subdeflection system used for correcting the mask distortion.
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85.40.Hp Lithography, masks and pattern transfer

Narrow cone emission from negative electron affinity photocathodes

Zhi Liu, Yun Sun, P. Pianetta, and R. F. W. Pease

J. Vac. Sci. Technol. B 23, 2758 (2005); http://dx.doi.org/10.1116/1.2101726 (5 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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The need for high brightness (e.g., 106 A cm−2 str−1 at 10 keV) electron sources is well established. Negative electron affinity (NEA) semiconductor structures have been studied for this application for several years. It has been argued that one advantage of these materials, particularly GaAs, is that the low effective mass, m*, of electrons in the semiconductor would lead to a narrow cone of emission, and hence increased brightness for a given current density, as a result of Snell’s Law. However this advantage would only apply if the electrons were emitted directly from the Γ-valley (with low m*) rather than indirectly, that is via scattering into the L-valley. We present here a direct experimental confirmation of this narrow cone of emission (semiangle 15°) and describe a quantitative model to account for the results. In photocathodes based on group III-nitride materials, the cone is predicted to be about twice as wide because of the larger values of m*.
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85.60.Ha Photomultipliers; phototubes and photocathodes
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Negative charging-up contrast formation of multilayered structures with a nonpenetrating electron beam in scanning-electron microscope

Motosuke Miyoshi and Katsumi Ura

J. Vac. Sci. Technol. B 23, 2763 (2005); http://dx.doi.org/10.1116/1.2101757 (6 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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In this article, we explain the contrast-formation mechanisms of the scanning-electron microscope for insulating samples under a nonpenetrating irradiation condition. Our fundamental point is that the detected secondary-electron signal current is only modified by the surface potential distribution. We propose a semiempirical model to explain the image contrast caused by excess negative-charge buildup on the surface of the insulating samples. The model treats the redistribution of secondary electrons and the contribution of tertiary electrons. The image-contrast formation mechanism of two typical examples is explained.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.49.Jk Electron scattering from surfaces
79.20.Hx Electron impact: secondary emission

Experimental optimization of the electron-beam proximity effect forward scattering parameter

M. Rooks, N. Belic, E. Kratschmer, and R. Viswanathan

J. Vac. Sci. Technol. B 23, 2769 (2005); http://dx.doi.org/10.1116/1.2062431 (6 pages) | Cited 5 times

Online Publication Date: 2 December 2005

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The electron-beam forward scattering parameter α characterizes the width of the incident beam plus an additional radius due to scattering of primary electrons in the resist. These “forward scattering” effects can be included in proximity-effect correction algorithms by using the point-spread energy function generated by a Monte Carlo simulation. Alternatively, correction algorithms may use a superposition of Gaussian functions to fit Monte Carlo simulations or to fit experimental data. Long-range (β>10 μm) effects due to electrons backscattered from the substrate are well characterized by simulations; however, forward scattering effects are difficult to model or measure. Experimental methods of measuring α include the exposure of dot arrays, line arrays, or so-called “doughnut” patterns over a large range of doses. Proximity parameters are then inferred indirectly through fitting line and dot widths. We have instead used a simpler and faster technique based on the method of [ Dubonos et al., Microelectron. Eng. 21, 293 (1993) ] which uses a liftoff technique to choose the optimal value of the forward scattering parameter α. We have applied this technique to determine α for 100 kV exposure of poly(methyl methacrylate) and KRS resists. Negative resist presents more of a challenge, and so a method of optimizing α for negative resists is presented. This work includes the variation of α as a function of resist thickness, and compares these values to those inferred from Monte Carlo simulations. We also discuss the dependence of α on resist developer and the effects of distortions from the developer meniscus.
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85.40.Hp Lithography, masks and pattern transfer

Dependence of linewidth and its edge roughness on electron beam exposure dose

M. Kotera, K. Yagura, and H. Niu

J. Vac. Sci. Technol. B 23, 2775 (2005); http://dx.doi.org/10.1116/1.2130357 (5 pages) | Cited 9 times

Online Publication Date: 2 December 2005

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Electron beam lithography simulation is presented. A line pattern edge roughness of a resist after development process is discussed based on simulations of electron scattering in the resist film and the resist development process. Fixed threshold energy model is applied for the simulation and variations of linewidth and the line edge roughness are obtained as functions of the incident electron energy, resist thickness, and electron doses. The energy range calculated is from 1 to 5 keV, the resist thickness ranges from 20 to 70 nm, and the electron dose ranges from 1 to 100 μC/cm2. The resist assumed is poly(methylmethacrylate) and the film is on a Si substrate. In the present study, the threshold energy density is determined as 1.44×1021 (eV/cm3) to draw a given linewidth of 100 nm, then the value of the line edge roughness is obtained. The minimum line edge roughness is obtained when the dose is more than that to produce the designed linewidth. As the dose is increased more than that to obtain the minimum edge roughness, the roughness increases with increasing the dose. For very large doses the roughness decreases with the dose, as it is explained by the statistical characteristics.
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85.40.Hp Lithography, masks and pattern transfer
61.80.Fe Electron and positron radiation effects
68.49.Jk Electron scattering from surfaces

Electron-beam direct writing system employing character projection exposure with production dispatching rule

T. Tominaga, K. Nakamae, T. Matsuo, H. Fujioka, T. Nakasugi, and K. Tawarayama

J. Vac. Sci. Technol. B 23, 2780 (2005); http://dx.doi.org/10.1116/1.2135793 (4 pages)

Online Publication Date: 2 December 2005

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An electron-beam direct writing (EBDW) system with a character projection (CP) aperture is a promising candidate as an effective maskless lithography tool to realize a system on a chip fabrication process at low cost with quick turn-around time. We have proposed an approach to enhance the throughput of an EBDW system by using a production dispatching rule. Through an event-driven simulation analysis in the backend of the line, the effect of production dispatching rules on the throughput and the cost in an EBDW system is evaluated. We considered four kinds of dispatching rules, FIFO, APA, LWKR, and SLACK. FIFO is a usually used dispatching rule and gives the highest priority to the waiting lot that came in first at the EB lithography process. In APA, the highest priority is given to the waiting lot that does not require the CP aperture exchange. In LWKR, the highest priority is given to the waiting lot associated with the job having the least amount of total processing time remaining to be done. In SLACK, the highest priority is given to the waiting lot with the shortest slack. Simulated result shows that the EBDW system with APA enhances the throughput more than 1.2 times as compared to that with FIFO, LWKR, or SLACK, and has a throughput of 5 wafers/h or more. Furthermore, compared with the cost per chip for FIFO, the APA rule reduces the cost/chip by more than 30% at the cost minimum lot arrival rate point.
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85.40.Hp Lithography, masks and pattern transfer

SnO2 lithographic processing for nanopatterned gas sensors

P. Candeloro, E. Comini, C. Baratto, G. Faglia, G. Sberveglieri, R. Kumar, A. Carpentiero, and E. Di Fabrizio

J. Vac. Sci. Technol. B 23, 2784 (2005); http://dx.doi.org/10.1116/1.2110371 (5 pages) | Cited 5 times

Online Publication Date: 2 December 2005

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Tin dioxide (SnO2) is widely used as sensing material in metal-oxides gas sensors. In this work we present two lithographic approaches for SnO2 patterning, an additive process and a subtractive one. In the first case patterns of SnO2 nanowires are successfully fabricated and exploited as sensing element in working devices; responses to several testing gases are satisfactorily improved with respect to continuous film devices. Regarding the subtractive process, we present reactive ion etching of SnO2 based on CF4/H2 gas mixture. Dependence of etch rate upon H2 concentration and effects due to Ar additions to plasma are investigated; results are discussed and a possible etching reaction is proposed, but further developments are required to increase the etch rate.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
81.07.Vb Quantum wires
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Visualization and in situ contacting of carbon nanotubes in a scanning electron microscope

M. D. Croitoru, G. Bertsche, D. P. Kern, C. Burkhardt, S. Bauerdick, S. Şahakalkan, and S. Roth

J. Vac. Sci. Technol. B 23, 2789 (2005); http://dx.doi.org/10.1116/1.2130350 (4 pages) | Cited 6 times

Online Publication Date: 2 December 2005

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A method for contacting carbon nanotubes on an insulating surface is presented. Tubes which are already connected to prefabricated electrodes can be visualized in the scanning electron microscope exploiting voltage contrast at low beam energies. Additional connections to tubes identified in this way are fabricated by in situ electron beam induced deposition from metalorganic precursors such as tungsten hexacarbonyl. A resistivity of 0.15 Ω cm before annealing has been achieved so far with this material.
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81.07.De Nanotubes
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments

Towards nano-fluidics by solvent deformation of electron beam resist

J. L. Pearson and D. R. S. Cumming

J. Vac. Sci. Technol. B 23, 2793 (2005); http://dx.doi.org/10.1116/1.2131876 (5 pages) | Cited 1 time

Online Publication Date: 2 December 2005

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Improvements in the fabrication technology of planar micro- and nano-fluidic systems are continually being sought. In this work, we demonstrate and characterize a potential method for making planar nano-fluidic channels in cross-linked UV-3 resist using a single-step electron-beam lithography process. Earlier work indicated that the fluids used in the resist development process influenced the final form of the nano-fluidic structures. In this study the development, rinsing and drying conditions for the resist processing have been investigated in detail to find the best conditions for channel formation. The process was then exploited to construct more complex planar nano-fluidic features, including Y- and T-shaped junctions that are required for practical systems.
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81.16.Nd Micro- and nanolithography
47.85.Np Fluidics
85.40.Hp Lithography, masks and pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
back to top Particle Beam Technologies

Ion implantation with scanning probe alignment

A. Persaud, J. A. Liddle, T. Schenkel, J. Bokor, Tzv. Ivanov, and I. W. Rangelow

J. Vac. Sci. Technol. B 23, 2798 (2005); http://dx.doi.org/10.1116/1.2062628 (3 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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We describe a scanning probe instrument which integrates ion beams with the imaging and alignment function of a piezoresistive scanning probe in high vacuum. The beam passes through several apertures and is finally collimated by a hole in the cantilever of the scanning probe. The ion beam spot size is limited by the size of the last aperture. Highly charged ions are used to show hits of single ions in resist, and we discuss the issues for implantation of single ions.
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07.79.-v Scanning probe microscopes and components
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.40.Hp Lithography, masks and pattern transfer

Mechanical characteristics and its annealing effect of diamondlike-carbon nanosprings fabricated by focused-ion-beam chemical vapor deposition

Ken-ichiro Nakamatsu, Masao Nagase, Jun-ya Igaki, Hideo Namatsu, and Shinji Matsui

J. Vac. Sci. Technol. B 23, 2801 (2005); http://dx.doi.org/10.1116/1.2132329 (5 pages) | Cited 10 times

Online Publication Date: 2 December 2005

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Our investigation of diamondlike-carbon (DLC) nanosprings with a 130-nm spring section diameter, which were fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD), showed for the first time that nanosprings can be stretched. We observed large displacements of the FIB-CVD nanosprings in situ optical microscopy; in other words, the nanosprings showed behavior similar to that of macroscale springs. In addition, we investigated the dependence of the spring constant of the DLC nanosprings on the spring diameter. The spring constants, measured using commercially available cantilevers, ranged from 0.47 to 0.07 N/m. The diameter dependence of the measured spring constant could be accurately expressed by the conventional formula for a coil spring. The estimated shear modulus of the DLC nanosprings was about 70 GPa. This value is very close to the value of conventional coil springs made of steel. Furthermore, We measured the stiffness of the annealed nanospring at 1000 °C in vacuum. The stiffness was decreased to approximately half compared to the stiffness of the spring without annealing.
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81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments

Cross beam lithography (FIB+EBL) and dip pen nanolithography for nanoparticle conductivity measurements

Stefano Cabrini, Robert J. Barsotti, Alessandro Carpentiero, Luca Businaro, Remo Proietti Zaccaria, Francesco Stellacci, and Enzo Di Fabrizio

J. Vac. Sci. Technol. B 23, 2806 (2005); http://dx.doi.org/10.1116/1.2062647 (5 pages) | Cited 5 times

Online Publication Date: 2 December 2005

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Focused ion beam lithography is a very powerful technique for directly writing patterns on many substrates, it is a maskless and resistless technique that allows a very wide range of applications, providing a resolution down to 10 nm. Using a system composed by a 30 keV gallium ion beam column plus a 30 keV electron beam, nanogaps for electrical measurements of nanoparticle were fabricated with a resolution down to the nanometer scale, by exploiting FIB milling (FIBM) and electron beam lithography (EBL). Starting from prepatterned samples a square pattern reduces the width of the gold wire and a narrow line pattern opens a gap of less than 7 nm. Electrical measurements and AFM tapping mode imaging were performed on the gaps. We patterned the ends of the gold leads with dip pen nanolithography using mercapto-undecanol (MUD) to form a bond between the nanoparticle and the alcohol group attached to the gold surface. After this assembly, devices showed an increase in conductivity (10–100-fold increase). Measuring the device again one week later, we saw almost no change in conductivity, showing that we deposit a multiparticle cluster and measure its conductivity.
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73.63.Bd Nanocrystalline materials
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
81.20.Wk Machining, milling
68.37.Ps Atomic force microscopy (AFM)

Writing the identity in radio frequency identity tags with focused ion-beam implantation of transistor gates

Anthony De Marco, William Bandy, Siavash Parsa, Henry Kaufmann, and John Melngailis

J. Vac. Sci. Technol. B 23, 2811 (2005); http://dx.doi.org/10.1116/1.2091092 (5 pages) | Cited 1 time

Online Publication Date: 2 December 2005

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The soon-to-be-ubiquitous radio frequency identity (RFID) tag consists of a Si chip (less than 1 mm2) attached to an antenna on a plastic sheet. Each tag needs to have a unique, electronically readable identity number. Currently, the preferred direction of industry appears to be to fabricate all chips the same, and then program the unique identity into the chip electrically in a permanent or semi-permanent fashion. This may make the tags reusable and permit the identity number to be written by the customer. On the other hand, writing the identity into the chips permanently, during fabrication has advantages; mainly, low cost, less real estate, and less vulnerability to tampering or accidental loss of identity. Permanent programming of the chip is currently done using selective laser cutting of metal connections on the chip, but has not been widely adopted because of cost and reliability. We propose an alternate method whereby transistors are substituted for the metal links and selectively focused-ion-beam (FIB) implanted to permanently turn some of them off. Moreover, we have demonstrated that a low ion dose ( ∼ 1012/cm2) is sufficient, so that the throughput is calculated to be practical. For post-fabrication implantation, the region above the transistor channel must be thinned to 100 to 200 nm to use reasonable ion energies. (Of course, in-process implantation is also an option before the passivation layer is applied.) We have used n-type metal oxide semiconductor (NMOS) and p-type metal oxide semiconductor (PMOS) test transistors fabricated at Berkeley and etched away the oxide and part of the poly over the gate. This process did not alter the transistor characteristics. The transistors were implanted with a series of doses and energies using both FIB and broad-beam implantation (Ar, As, and B with broad-beam and Ga, As, and B with FIB). The required dose to turn transistors off is of order 1012/cm2 as long as the ions have sufficient energy to alter the gate oxide and/or the channel. In PMOS transistors there is a strong shift in threshold voltage as well as a decrease in drain current, while in NMOS the main effect is the latter. Since Ga+ ions work, a robust FIB system can be used to implant the RFID tags. Moreover, neither high resolution nor high placement accuracy are needed. We only need to implant a given transistor without implanting its neighbors. Assuming a 200 mm wafer with 30 000 chips, 120 transistors per chip, 2 μm2 gate area, and a 100 pA beam current results in an implant time of 6 min/wafer. Using a write-on-the-fly scheme the wafer would have to be scanned at 6 cm/s. Since 50 μs are needed to implant each transistor, deflection and blanking times should not be limitations.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Analytical model of a gas phase field ionization source

Xuefeng Liu and Jon Orloff

J. Vac. Sci. Technol. B 23, 2816 (2005); http://dx.doi.org/10.1116/1.2127946 (5 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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High resolution focused ion beam technology is based on the use of field ionization sources. The most widely used source by far is the liquid metal ion source (LMIS) and most focused ion beam systems today employ it. The gas phase field ionization source (GFIS) is hardly employed today except in field ionization microscopy, but present day technology would allow its unique properties vis a vis the liquid metal ion source, including smaller virtual source size and energy spread, and the ability to produce ions from H, He, and heavier noble gases, to be exploited. If the GFIS is used as an ion source for a focusing column it would be useful to be able to calculate its emission properties (current versus voltage) as a function of emitter shape (a parameter not variable in a LMIS). Such a calculation had not been done precisely based on realistic emitter shapes. In this work, a theoretical description of the mechanism for ion production in a GFIS is presented. The comparison of the result with the experimental data for a H2–Ir GFIS is given, which shows reasonable agreement. With the present model, when used with the model for the optical properties of the GFIS (to be published), a focused ion beam (FIB) optical designer can make reasonable predictions about the properties of a GFIS-based FIB. Based on the modeling, we predict that a sub 1 nm beam of He+ should be possible with ∼ 1 pA current.
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79.70.+q Field emission, ionization, evaporation, and desorption

Electrical properties of nanocontacts on silicon nanoparticles embedded in thin SiO2 synthesized by ultralow energy ion implantation

G. Ben Assayag, M. Shalchian, H. Coffin, A. Claverie, J. Grisolia, C. Dumas, and S. M. Atarodi

J. Vac. Sci. Technol. B 23, 2821 (2005); http://dx.doi.org/10.1116/1.2132335 (4 pages)

Online Publication Date: 2 December 2005

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In this paper, we present the room temperature current-voltage characteristics of large (100×100 μm2) and a nanoscale (100×100 nm2) metal-oxide-semiconductor (MOS) capacitor containing few silicon nanocrystals. The layer of silicon crystals is synthesized within the oxide of this capacitor by ultralow energy ion implantation and annealing. Current fluctuations in the form of discrete current steps and sharp peaks are apparent in the static and dynamic I(V) characteristics of the capacitor. These features have been associated to quantized charging and discharging of the nanoparticles and the resulting Coulomb interaction to the tunneling current.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

Growth and simulation of high-aspect ratio nanopillars by primary and secondary electron-induced deposition

J. D. Fowlkes, S. J. Randolph, and P. D. Rack

J. Vac. Sci. Technol. B 23, 2825 (2005); http://dx.doi.org/10.1116/1.2101732 (8 pages) | Cited 32 times

Online Publication Date: 2 December 2005

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While several studies have suggested that secondary electrons dominate electron beam induced deposition (EBID), we demonstrate that primary electrons (PE’s) contribute significantly to the deposition for nanoscale EBID over the electron beam energy range (500–20 keV). High-aspect ratio pillar growth is a signature of EBID; W nanopillar growth on SiO2 substrate yielded a growth rate of 6 nm s−1 and a nanopillar aspect ratio of ∼ 50. A simple integration of the primary, secondary, and backscattered electron distributions versus a dissociation cross section for WF6 suggests that all three electron species should contribute to the total volume of the deposited nanopillar, contrary to reports that suggest that secondary electrons dominate the process. A three-dimensional, Monte Carlo simulation including time correlated gas dynamics and species specific deposition was developed to help elucidate which of the relevant electron species, primary (PE’s), secondary (SE’s), and/or backscattered electrons (BSE’s), induce the dissociation of precursor gas and lead to nanopillar growth. PE’s and secondary electrons produced from the incident beam (SEI’s) were found to induce the vertical nanopillar growth component relative to secondary electrons induced from backscattered electrons (SEII’s) and BSE’s.
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81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials

Development of a multi-electron-beam source for sub-10 nm electron beam induced deposition

M. J. van Bruggen, B. van Someren, and P. Kruit

J. Vac. Sci. Technol. B 23, 2833 (2005); http://dx.doi.org/10.1116/1.2091087 (7 pages) | Cited 12 times

Online Publication Date: 2 December 2005

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A multibeam electron beam induced deposition (EBID) system is presented that aims at the fabrication of sub-10 nm structures with EBID. This system consists of a multibeam source (MBS) module, delivering 100 virtual sources and a standard scanning electron microscope column to image the 100 sources onto a wafer. In this paper, the concept for the MBS is presented: starting with a single Schottky field emission gun, its broad beam is divided into 100 individually focused sub-beams. This is accomplished with an aperture plate with small current-limiting apertures on the side irradiated by the beam and larger holes on the other side, acting as aperture lenses due to the presence of a macroelectrode in front of it. With this concept, in addition to the miniature aperture lenses, a negative macrolens effect is established that can serve to compensate for both the third-order geometric and first-order chromatic aberration of the collimator lens in front of the aperture plate. A simple aberration model is presented to illustrate this, and first results are shown of a prototype MBS.
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41.75.Fr Electron and positron beams
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
07.77.Ka Charged-particle beam sources and detectors
back to top EUV Lithography

Characterization of the synchrotron-based 0.3 numerical aperture extreme ultraviolet microexposure tool at the Advanced Light Source

Patrick Naulleau, Jason P. Cain, Erik Anderson, Kim Dean, Paul Denham, Kenneth A. Goldberg, Brian Hoef, and Keith Jackson

J. Vac. Sci. Technol. B 23, 2840 (2005); http://dx.doi.org/10.1116/1.2127940 (4 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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Synchrotron-based extreme ultraviolet (EUV) exposure tools continue to play a crucial roll in the development of EUV lithography. Utilizing a programmable-pupil-fill illuminator, the 0.3 numerical aperture (NA) microexposure tool at Lawrence Berkeley National Laboratory’s Advanced Light Source synchrotron radiation facility provides the highest resolution EUV projection printing capabilities available today. This makes it ideal for the characterization of advanced resist and mask processes. The Berkeley tool also serves as a good benchmarking platform for commercial implementations of 0.3 NA EUV microsteppers because its illuminator can be programmed to emulate the coherence conditions of the commercial tools. Here we present the latest resist and tool characterization results from the Berkeley EUV exposure station.
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85.40.Hp Lithography, masks and pattern transfer

Measuring line roughness through aerial image contrast variation using coherent extreme ultraviolet spatial filtering techniques

Michael D. Shumway, Patrick Naulleau, Kenneth A. Goldberg, and Jeffrey Bokor

J. Vac. Sci. Technol. B 23, 2844 (2005); http://dx.doi.org/10.1116/1.2134717 (4 pages) | Cited 2 times

Online Publication Date: 2 December 2005

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Line edge roughness properties for an extreme ultraviolet photoresist (Rohm and Haas/Shipley 1 K) were investigated by varying the aerial image contrast of dense line and space patterns. Aerial image contrast variation was performed in single exposures by programming the modulation information on the mask. No background flood exposures were needed to reduce the contrast. The Micro Exposure Tool at Lawrence Berkeley National Laboratory was used for these experiments. Dense 50 nm lines and spaces were printed with contrast levels ranging from 86.4% to 46.8%. Coherence was programmed to be 0.1 for these experiments. Results show that an increase in the aerial image contrast causes a subsequent decrease in the line edge roughness (LER). Similar effects are seen for linewidth roughness (LWR). The LER varied from 3.3 nm (at 86.4% contrast) to 8.0 nm (at 46.8% contrast). LWR varied from 5.3 nm (at 86.4% contrast) to 12.8 nm (at 46.8% contrast). All values are three sigma root-mean-square. Only a couple of dense 30 nm features would print in this configuration. For these 30 nm lines and spaces, the best LER was 5.6 nm and LWR was 11.3 nm.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Scaling law in acceleration test of extreme ultraviolet lithography projection optics mirror contamination

Yoshio Gomei, Hiromitsu Takase, Takashi Aoki, Shuichi Matsunari, Shigeru Terashima, Yukinobu Kakutani, and Masahito Niibe

J. Vac. Sci. Technol. B 23, 2848 (2005); http://dx.doi.org/10.1116/1.2074847 (4 pages) | Cited 3 times

Online Publication Date: 2 December 2005

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A model to describe surface physics in extreme ultraviolet lithography (EUVL) optics mirror contamination is proposed. Photon-induced desorption is a key process in determining the surface areal density of the related adsorbed gas species when irradiating power is high. Scaling law for acceleration test is analyzed and experiment was performed by using synchrotron undulator radiation. It appears that oxidation on a Si capping layer is almost anti-linearly dependent on photon intensity and acceleration test can be conducted by increasing the H2O pressure linearly with photon intensity increase. In contrast, it was found that carbon deposition does not linearly scale to photon intensity. Special care is necessary in understanding results conducted in accelerated conditions as well as under different pulse duty conditions.
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81.65.Mq Oxidation
85.40.Hp Lithography, masks and pattern transfer
68.43.Tj Photon stimulated desorption

Mask defect inspection using an extreme ultraviolet microscope

K. Hamamoto, Y. Tanaka, S. Y. Lee, N. Hosokawa, N. Sakaya, M. Hosoya, T. Shoki, T. Watanabe, and H. Kinoshita

J. Vac. Sci. Technol. B 23, 2852 (2005); http://dx.doi.org/10.1116/1.2127943 (4 pages) | Cited 11 times

Online Publication Date: 2 December 2005

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A defect inspection technique on an extreme ultraviolet lithography mask is described. There are two kinds of defects, amplitude defects and phase defects due to the multilayer coating. The technique utilizes a microscope using the same 13.5 nm wavelength as the light used for exposure, and producing a magnified image of defects on a mask. Using this microscope, amplitude defects on practical masks and phase defects are observed. A phase defect was formed by a multilayer coated on a line pattern with a height of 5 nm and width of 90 nm on a glass substrate. Although the detected defect is made beforehand, it is detected by reflection of the light which penetrated inside of a multilayer. These results show that it is possible to detect the internal reflectivity distribution, without depending on surface perturbations.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
07.60.-j Optical instruments and equipment

Predicting the dynamic response of an extreme ultraviolet reticle during exposure scanning

G. Dicks, A. Mikkelson, R. Engelstad, and E. Lovell

J. Vac. Sci. Technol. B 23, 2856 (2005); http://dx.doi.org/10.1116/1.2101765 (4 pages) | Cited 1 time

Online Publication Date: 2 December 2005

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Extreme ultraviolet (EUV) masks are expected to experience up to 6 g’s of acceleration and achieve speeds as high as 500 mm/s while mounted in the exposure tool. Therefore, it is critical that the mounting technique employed to hold the mask in position prevents the mask from slipping under these conditions. An electrostatic pin chuck must generate adequate pressure between the mask and chuck, as well as a sufficient amount of friction. To ensure the success of such a mount design, three-dimensional finite element (FE) models have been created to predict the conditions necessary to prevent mask slippage during exposure scanning. The FE modeling is used to predict the influence of the initial substrate backside surface shape on mask flatness when mounted in the chuck, as well as the effects of friction on the relative displacement between the reticle and chuck. Simulation results indicate that for typical EUV mask substrates, coefficients of friction greater than 0.2 are necessary to prevent bulk displacement of the mask during the acceleration duty cycle. Larger coefficients may be required to limit local in-plane displacements, depending upon the initial backside shape.
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85.40.Hp Lithography, masks and pattern transfer

Printability of nonsmoothed buried defects in extreme ultraviolet lithography mask blanks

Vincent Farys, Christelle Charpin-Nicolle, Marieke Richard, Jean-Yves Robic, Viviane Muffato, Etienne Quesnel, Sergeï Postnikov, Patrick Schiavone, Maxime Besacier, Rafik Smaali, and Patrick Naulleau

J. Vac. Sci. Technol. B 23, 2860 (2005); http://dx.doi.org/10.1116/1.2135293 (6 pages)

Online Publication Date: 2 December 2005

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One of the most important challenges in extreme ultraviolet lithography is the need to provide mask blanks free of defects. In order to provide experimental results on the printability of buried defects, a dedicated extreme ultraviolet (EUV) mask blank was manufactured using ion beam sputtering (IBS) with a nonsmoothing process. Using this kind of process, the effect of the buried defect is apparent throughout the entire multilayer stack. The disturbance generated in the multilayer, measured using an atomic force microscope (AFM), shows lateral growth and a slight vertical smoothing effect. Here we report the printability results obtained with this kind of defect. One result concerns the influence of the defect density on the printability. We show that the major effect can be attributed to local flare, which depends on the pattern density. In order to better understand the printability mechanism of this kind of buried defect, we also compared the experimental results with electromagnetic simulation.
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85.40.Hp Lithography, masks and pattern transfer

Investigation of multilayer structural changes in phase and amplitude-defects correction process

Seung Yoon Lee, Tae Geun Kim, Jae Gun Park, Joo Kyoung Song, Oh Hyun Kim, Chul-Woong Yong, and Jinho Ahn

J. Vac. Sci. Technol. B 23, 2866 (2005); http://dx.doi.org/10.1116/1.2134715 (4 pages)

Online Publication Date: 2 December 2005

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Controlling defects on the extreme ultraviolet lithography (EUVL) mask has become a critical issue among many EUVL element technologies. We have conducted experiments to investigate the correctability of two kinds of major defect types, phase and amplitude defects. Phase defects correctability was addressed by using the electron-beam local heating method and amplitude defects correctability were done by using the focused ion-beam (FIB). Additionally, two kinds of multilayers, Mo/Si and Mo/Ru/Si, were used as substrates to inspect the behavior in a comparative way. As a result, the sink brought by electron-beam (e-beam) localized heating on a planar multilayer surface was about 8 and 13.6 nm in Mo/Si and Mo/Ru/Si multilayers, respectively, under the e-beam dose of 250 μC/cm2. However, the heating effect was limited to within a few layers from the surface. FIB etching was also conducted on a planar surface of a multilayer. There are two types of FIB correction methods, image mode and spot mode. The etched area was relatively large ( ∼ 3 μm×3 μm) in image mode. But in the spot mode, the etched area could be confined to a few tens of nanometers in diameter. This FIB method also caused some damage on the multilayer surface.
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68.65.Ac Multilayers
61.72.-y Defects and impurities in crystals; microstructure
81.65.Cf Surface cleaning, etching, patterning

Asymmetry of aerial image after mask pattern correction for off-axis incident light in extreme ultraviolet lithography

Minoru Sugawara, Iwao Nishiyama, and Mikio Takai

J. Vac. Sci. Technol. B 23, 2870 (2005); http://dx.doi.org/10.1116/1.2135294 (5 pages) | Cited 3 times

Online Publication Date: 2 December 2005

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In extreme-ultraviolet lithography (EUVL), asymmetry in printed images arises from the off-axis incidence of light illuminating the mask and from the thicknesses of the absorber and buffer layers of the mask. This study examined whether or not the asymmetry of printed images due to off-axis incidence affected pattern edge position error. The pattern edge position error and asymmetry of printed images were investigated using two types of patterns with a critical dimension (CD) of 44 nm: nested lines, because they induce asymmetry in the printed image for off-axis incidence even though the mask layout is perfectly symmetrical and T-shaped patterns. The amount of pattern edge position error was found to be almost the same for off-axis and normal incidence, irrespective of the larger asymmetry in the printed image for off-axis incidence, even for thick absorber and buffer layers.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Imaging characteristics and specification of mask mean-to-target and mask uniformity according to polarization status

Sung-Woo Lee, Jo Finders, Suk-Joo Lee, Sang-Gyun Woo, and Han-Ku Cho

J. Vac. Sci. Technol. B 23, 2875 (2005); http://dx.doi.org/10.1116/1.2110307 (4 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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Maximum exposure latitude (EL), mask error enhancement factor (MEEF), and intrafield critical dimension (CD) uniformity are compared in TE and unpolarized (UNP) light. An ArF dry scanner with 0.85 numerical aperture and dipole illumination with inner and outer sigmas of 0.93 and 0.69 is used. 63 and 73 nm nodes are chosen which have 126 and 146 nm pitch sizes and Target CDs of 63 and 73 nm. TE shows 56% and 10% larger maximum EL than UNP for 63 and 73 nm nodes, respectively. TE shows 56% increased IFU compared with UNP at the 63 nm node. MEEFs are 3.4 and 4.1 for TE and UNP light at the 63 nm node, respectively. MEEFs of 1.4 and 1.5 are observed for TE and UNP light at the 73 nm node. Mask mean-to-target (MTT) and uniformity specifications are compared according to polarization status. For the 63 nm node, specifications of mask MTTs are ±1.28 and ±1.28 nm and the mask uniformities are 1.43 and 1.18 nm for TE and UNP light, respectively. For the 73 nm node, ±2.62 and ±2.43 nm of the mask MTT specifications are obtained with mask uniformities of 4.04 and 3.77 nm at TE and UNP light. TE light shows 28% and 11% larger MTT and uniformity specification areas than UNP light for 63 and 73 nm nodes.
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85.40.Hp Lithography, masks and pattern transfer

Ion emission measurements and mirror erosion studies for extreme ultraviolet lithography

K. Takenoshita, C.-S. Koay, S. George, S. Teerawattansook, M. Richardson, and V. Bakshi

J. Vac. Sci. Technol. B 23, 2879 (2005); http://dx.doi.org/10.1116/1.2131879 (6 pages) | Cited 3 times

Online Publication Date: 2 December 2005

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Mirror erosion by high energy ion emission from extreme UV light sources is one of the main factors contributing to EUVL collector mirror reflectivity degradation. We are measuring ion energy distributions at the mirror distance from the plasma utilizing three different ion diagnostics for the case of tin-doped microscopic droplet laser plasmas. Typical ion energy distributions measured by an electrostatic spectrometer are described. From the ion energy distributions, an estimate of mirror erosion is obtained. The effectiveness of electrostatic field mitigation is evaluated for the EUVL source requirement.
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52.70.Ds Electric and magnetic measurements
42.88.+h Environmental and radiation effects on optical elements, devices, and systems
42.79.Bh Lenses, prisms and mirrors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
52.25.Tx Emission, absorption, and scattering of particles
52.50.Dg Plasma sources

Extreme ultraviolet focus sensor design optimization

Kenneth A. Goldberg, Maureen M. Teyssier, and J. Alexander Liddle

J. Vac. Sci. Technol. B 23, 2885 (2005); http://dx.doi.org/10.1116/1.2134719 (6 pages)

Online Publication Date: 2 December 2005

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We describe performance modeling and design optimization of a prototype extreme ultraviolet (EUV) focus sensor (FS) designed for use with existing 0.3 numerical aperature (NA) EUV projection-lithography tools. At 0.3 NA and 13.5 nm wavelength, the depth of focus at the resolution limit shrinks to 150 nm increasing the importance of high-sensitivity focal-plane-detection tools. The FS is a free-standing Ni grating structure that works in concert with a simple mask pattern of regular lines and spaces at constant pitch. The FS pitch matches that of the image-plane aerial-image intensity: it transmits the light with high efficiency when the grating is aligned with the aerial image laterally and longitudinally. Using a single-element photodetector, to detect the transmitted flux, the FS is scanned laterally and longitudinally so the plane of peak aerial-image contrast can be found. The design under consideration has a fixed image-plane pitch of 80 nm, with aperture widths of 12–40 nm (1–3 wavelengths), and aspect ratios of 2–12. TEMPEST-3D is used to model the light transmission. Careful attention is paid to the annular, partially coherent, unpolarized illumination and to the annular pupil of the Micro-Exposure Tool optics for which the FS is designed. The system design balances the opposing needs of high sensitivity and high throughput optimizing the signal-to-noise ratio in the measured intensity contrast.
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42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.15.Eq Optical system design

Electrical characterization of multilayer masks for extreme ultraviolet lithography

J. G. Hartley, S. Raghunathan, and A. Govindaraju

J. Vac. Sci. Technol. B 23, 2891 (2005); http://dx.doi.org/10.1116/1.2062607 (5 pages) | Cited 1 time

Online Publication Date: 2 December 2005

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Voltage potentials on the surface of a mask blank form one of the mechanisms by which errors in mask patterning may be introduced. When electrical currents flow through the mask either from the patterning beam or induced through other means, it is the impedance to ground from the point being patterned on the mask that determines the potential developed. Ten multilayer coated mask blanks from four sources were provided by Sematech for electrical characterization. The initial purpose of this project is to experimentally determine the resistance between various points in the quality area to likely ground locations on the mask. The mask can be grounded on the top, side or bottom edges. Initial attempts to characterize the resistance with a variety of measurement tools proved to be inconsistent. A test fixture was then assembled to enable voltage-current (V-I) characteristic measurements to be made on the samples. Several key issues were observed. First, the behavior was not very stable—the V-I characteristics were observed to transition between several different resistance modes. Second, quite a few of the modes observed exhibited semiconductor-like behavior. We have included representative examples of the results. Details of the experimental setup and the results obtained from the samples are presented and the behavior is explained.
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85.40.Hp Lithography, masks and pattern transfer
back to top X-ray Lithography

Development, installation, and performance of the x-ray stepper JSAL 5C

Q. Leonard, D. Malueg, J. Wallace, J. W. Taylor, S. Dhuey, F. Cerrina, B. Boerger, R. Selzer, M. Yu, Y. Ma, K. Myers, M. Trybendis, E. Moon, and H. I. Smith

J. Vac. Sci. Technol. B 23, 2896 (2005); http://dx.doi.org/10.1116/1.2121711 (7 pages)

Online Publication Date: 2 December 2005

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We show the first results from a newly-operation advanced x-ray stepper, and describe an improved type of x-ray mask for use on it. The Mod 5C is the newest x-ray stepper developed by JMAR (JSAL Nanolithography). It is configured for installation at the Center for NanoTechnology (CNTech) on a synchrotron radiation port of the Aladdin storage ring. The alignment system is based on a new IBBI detection system with demonstrated subnanometer resolution. For this system, three microscopes are used for detecting the misalignment between wafer and mask marks with the error signal fed back in the mask positioning stage with the mask locked to the wafer stage through the use of a high-resolution laser interferometer. Both field-by-field and global alignment techniques are possible, and multiple wafer sizes can be used with a NIST format mask held in a kinematic mount, with a gap setting capable of adjustment between 2 and 50 microns. A novel beam scanning system was installed to deliver a uniform exposure over a field of 35×35 mm2 field. The high power from the storage ring allows exposure times in chemically amplified resists of 5–10 s for the CNTech-designed beamline; shorter exposure times could be achieved with a refocusing beamline, and the stepper can be configured for an x-ray point source. To achieve sub-35 nm resolution requires very small gaps. A new type of mask had to be developed, on the basis of the mesa mask originally developed at MIT. A very high flatness is required to maintain a parallel mask-wafer exposure environment. Currently, for low cost and easy manufacturing, we employ gold-plated absorber masks with a silicon nitride membrane. From the initial exposures, the resolution achieved is below 50 nm with exposure conditions described. The issues of the resolution of the exposure tool are addressed and compared to the outcomes from detailed modeling.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Large area and wide dimension range x-ray lithography for lithographite, galvanoformung, and abformung process using energy variable synchrotron radiation

Yuichi Utsumi and Takefumi Kishimoto

J. Vac. Sci. Technol. B 23, 2903 (2005); http://dx.doi.org/10.1116/1.2131880 (7 pages) | Cited 10 times

Online Publication Date: 2 December 2005

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We developed an x-ray lithography system for the “lithographite, galvanoformung, and abformung” process using synchrotron radiation at the NewSUBARU facility of the University of Hyogo, Hyogo, Japan. The x-ray lithography system can utilize two different energy regions: one is a high-energy region: from 2 to 12 keV, and the other is a low-energy region from 1 to 2 keV. Each energy region can be selected in accordance with the size and shape of the desired microstructures. Large-area patterning across an A4-size area was successfully performed with a highly uniform pattern thickness. Furthermore, high-aspect-ratio patterning using a high-x-ray-energy region was also achieved using this x-ray lithography system.
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85.40.Hp Lithography, masks and pattern transfer

Functionalized SU-8 patterned with x-ray lithography

S. Balslev and F. Romanato

J. Vac. Sci. Technol. B 23, 2910 (2005); http://dx.doi.org/10.1116/1.2062651 (4 pages) | Cited 2 times

Online Publication Date: 2 December 2005

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In this work we demonstrate the feasibility of x-ray lithography on SU-8 photoresist doped with the laser dye Rhodamine 6G, while retaining the photoactive properties of the embedded dye. Two kinds of structures are fabricated via soft x-ray lithography and characterized: a laser and an amplified spontaneous emission light source that couples out light normal to the chip plane. In addition we examine the influence of the x-ray irradiation on the fluorescence of thin films of dye doped SU-8. The dye embedded in the SU-8 is optically excited during characterization by an external light source tuned to the absorption band of the dye.
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85.40.Hp Lithography, masks and pattern transfer
back to top Nanoimprint Techniques

4 inch lift-off process by trilayer nanoimprint lithography

J. Tallal, K. Berton, M. Gordon, and D. Peyrade

J. Vac. Sci. Technol. B 23, 2914 (2005); http://dx.doi.org/10.1116/1.2130351 (6 pages) | Cited 3 times

Online Publication Date: 2 December 2005

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We present the development of a reliable 4 in. lift-off process based on trilayer nanoimprint lithography (NIL). At first, an inductively coupled plasma etching step of the imprinted resist is used to remove the residual resist thickness after NIL for different pattern geometry and density, while maintaining the critical dimensions of the studied patterns. By combining this etching step to a trilayer (NEB22/Ti/PMMA) nanoimprint process, reproductible 4 in. wafer lift-off of 250 nm wide metallic patterns was obtained. Finally, local probe indentation measurements are investigated to correlate the mechanical properties of different imprinted polymers to the achievable nanogap replication.
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81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Fabrication of three-dimensional stamps for embossing techniques by lithographically controlled isotropic wet etching

Massimo Tormen, Alessandro Carpentiero, Lisa Vaccari, Matteo Altissimo, Enrico Ferrari, Dan Cojoc, and Enzo Di Fabrizio

J. Vac. Sci. Technol. B 23, 2920 (2005); http://dx.doi.org/10.1116/1.2130348 (5 pages) | Cited 4 times

Online Publication Date: 2 December 2005

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The excellent characteristics that nanoimprint lithography (NIL) shows as a two-dimensional patterning technique, such as resolution and throughput, are shared with its three-dimensional (3D) structuring version. Nevertheless, the potentialities of NIL for 3D structuring remain largely unexplored and unexploited, hindered by the difficulties in the fabrication of high quality masters with throughput suitable for practical purposes. We present a technique that allows production of stamps with tightly controlled three-dimensional profiles in the 10 nm–100 μm scale range. This technique consists of a sequence of lithographic steps alternated with isotropic wet etching processes performed on a quartz substrate. Scanning electron microscopy and atomic force microscopy characterization shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be formed with this method. Quartz stamps have been employed in nanoimprint, hot embossing, or casting processes to shape complex plastic elements. This technique is expected to have many applications in different nanotechnology-related fields such as optics, nanomechanics, microfluidics, and plasmon nano-optics.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)

Ultraviolet-based nanoimprint at reduced environmental pressure

A. Fuchs, M. Bender, U. Plachetka, U. Hermanns, and H. Kurz

J. Vac. Sci. Technol. B 23, 2925 (2005); http://dx.doi.org/10.1116/1.2132325 (4 pages) | Cited 11 times

Online Publication Date: 2 December 2005

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The essential role of environmental pressure during ultraviolet-based nanoimprint is demonstrated for a series of relevant lithographic properties.
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81.16.Nd Micro- and nanolithography
81.10.Fq Growth from melts; zone melting and refining

Enhanced molecular patterning via microdisplacement printing

Arrelaine A. Dameron, Jennifer R. Hampton, Susan D. Gillmor, J. Nathan Hohman, and Paul S. Weiss

J. Vac. Sci. Technol. B 23, 2929 (2005); http://dx.doi.org/10.1116/1.2135794 (4 pages) | Cited 13 times

Online Publication Date: 2 December 2005

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Here we demonstrate the versatility of “microdisplacement printing,” a soft lithographic patterning technique that employs microcontact printing to replace pre-formed self-assembled monolayers (SAMs) selectively. We use molecules that are common in microcontact printing as well as low-molecular-weight molecules that cannot be patterned by traditional methods. Multiple component SAMs were fabricated by additional processing steps, extending microdisplacement printing to more complex patterns.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of 1/4 wave plate by nanocasting lithography

Takashi Yoshikawa, Takaaki Konishi, Masaki Nakajima, Hisao Kikuta, Hiroaki Kawata, and Yoshihiko Hirai

J. Vac. Sci. Technol. B 23, 2939 (2005); http://dx.doi.org/10.1116/1.2127953 (5 pages) | Cited 13 times

Online Publication Date: 2 December 2005

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Nanocasting lithography is one of the convenient ways to fabricate micronanostructures using various kinds of polymers without special tools. Nanocasting lithography is demonstrated for a 50 nm half-pitch pattern, high-aspect-ratio micropillars, and high-aspect-ratio nanogratings for wave plates. The defect, which is caused by an air bubble in the sub-100 nm pattern, is successfully eliminated by vacuum baking after spin coating of a polymer. Also, a high-aspect-ratio structure having 400 nm pitch and 1.9 μm height was successfully fabricated by polycarbonate for 2000×200 μm. These structures show a 1/5 wave shift for the 633 nm wavelength.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.86.+b Optical workshop techniques
42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
81.20.-n Methods of materials synthesis and materials processing

Topas-based lab-on-a-chip microsystems fabricated by thermal nanoimprint lithography

B. Bilenberg, M. Hansen, D. Johansen, V. Özkapici, C. Jeppesen, P. Szabo, I. M. Obieta, O. Arroyo, J. O. Tegenfeldt, and A. Kristensen

J. Vac. Sci. Technol. B 23, 2944 (2005); http://dx.doi.org/10.1116/1.2091089 (6 pages) | Cited 14 times

Online Publication Date: 2 December 2005

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We present a one-step technology for fabrication of Topas-based lab-on-a-chip (LOC) microsystems by the use of thermal nanoimprint lithography (NIL). The technology is demonstrated by the fabrication of two working devices: a particle separator and a LOC with integrated optics for absorbance measurements. These applications demonstrate the fabrication of millimeter to micrometer-sized structures in one lithographic step. The use of NIL makes the technology easily scalable into the nanometer regime by the use of a suitable lithographic technique in the fabrication of the stamp. Processing issues such as environmental stress cracking of the Topas and the requirements to anti-sticking layers on the stamp when imprinting into Topas are discussed.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

High performance 100 mm-in-diameter true zero-order waveplates fabricated by imprint lithography

Jian Jim Wang, Xuegong Deng, Feng Liu, Lei Chen, Anguel Nikolov, Xiaoming Liu, Jiandong Deng, and Paul Sciortino

J. Vac. Sci. Technol. B 23, 2950 (2005); http://dx.doi.org/10.1116/1.2062430 (4 pages) | Cited 2 times

Online Publication Date: 2 December 2005

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Commercial quality high-performance true zero-order quarter waveplates based on artificial dielectric nanostructures were made by high throughput and low cost wafer-based nanofabrication processes. Both precise phase retardation (90°±2° across a 100 mm-in-diameter glass wafer) and a high transmittance (>98.8%) were achieved. The quarter waveplates with different center wavelengths, such as, 780 nm and 660 nm, have been fabricated for optical pick-up (CD/DVD) applications. The nanostructure based true zero-order quarter waveplates are operational at a large wavelength and temperature range under a wide incident angle. The developed high quality true zero-order quarter waveplates have the potential for many cost-sensitive optical applications. Furthermore, it opens the potential for integrated optical applications thanks to the nanofabrication processes.
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42.79.Ci Filters, zone plates, and polarizers
81.16.Nd Micro- and nanolithography
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques

Three-dimensional polymer structures fabricated by reversal ultraviolet-curing imprint lithography

N. Kehagias, M. Zelsmann, C. M. Sotomayor Torres, K. Pfeiffer, G. Ahrens, and G. Gruetzner

J. Vac. Sci. Technol. B 23, 2954 (2005); http://dx.doi.org/10.1116/1.2130349 (4 pages) | Cited 8 times

Online Publication Date: 2 December 2005

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Polymer optical devices could be an alternative to dielectric or semiconductor devices, since they can be fabricated using low-cost processes with high manufacturing output. This article presents results on the fabrication of polymer optical device-like and three-dimensional structures using the imprint and reversal imprint techniques. This last technique offers the unique advantage of printing over nonflat surfaces allowing a layer-by-layer fabrication of three-dimensional structures. Depending on the size and density of the stamp features, a “whole layer transfer” mode or an “inking” mode can be observed. The same printable ultraviolet cross-linkable polymer (mr-L 6000 from Micro Resist Technology) has been used at each repetition of the fabrication process so that the number of layers that can be stacked onto a substrate is no longer limited by the polymer glass transition temperature (Tg), unlike previous results where different polymers with a decreasing Tg had to be used for the successive layers.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.-x Polymers: properties; reactions; polymerization
81.16.Nd Micro- and nanolithography

Simulations of nonuniform embossing: The effect of asymmetric neighbor cavities on polymer flow during nanoimprint lithography

Harry D. Rowland, William P. King, Amy C. Sun, and P. Randy Schunk

J. Vac. Sci. Technol. B 23, 2958 (2005); http://dx.doi.org/10.1116/1.2127939 (5 pages) | Cited 30 times

Online Publication Date: 2 December 2005

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This article presents continuum simulations of viscous polymer flow during nanoimprint lithography (NIL) for embossing tools having irregular spacings and sizes. Simulations vary nonuniform embossing tool geometry to distinguish geometric quantities governing cavity filling order, polymer peak deformation, and global mold filling times. A characteristic NIL velocity predicts cavity filling order. In general, small cavities fill more quickly than large cavities, while cavity spacing modulates polymer deformation mode. Individual cavity size, not total filling volume, dominates replication time, with large differences in individual cavity size resulting in nonuniform, squeeze flow filling. High density features can be modeled as a solid indenter in squeeze flow to accurately predict polymer flow and allow for optimization of wafer-scale replication. The present simulations make it possible to design imprint templates capable of distributing pressure evenly across the mold surface and facilitating symmetric polymer flow over large areas to prevent mold deformation and nonuniform residual layer thickness.
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62.10.+s Mechanical properties of liquids
81.16.Nd Micro- and nanolithography
47.11.-j Computational methods in fluid dynamics

Polymer time constants during low temperature nanoimprint lithography

H.-C. Scheer, N. Bogdanski, M. Wissen, T. Konishi, and Y. Hirai

J. Vac. Sci. Technol. B 23, 2963 (2005); http://dx.doi.org/10.1116/1.2121727 (4 pages) | Cited 15 times

Online Publication Date: 2 December 2005

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We investigate low temperature nanoimprint into polymers, where adequate pressure choice helps to increase the imprint velocity of larger patterns und thus decreases pattern size effects by reduction of the effective viscosity. In order to make use of shear rate effects, the imprint has to be performed within the viscoelastic plateau region and not in the viscous flow regime of the polymer. Therefore elastic effects play an important role and may lead to shape recovery of the polymer after imprint. We address the counter play of elastic effects and viscous flow by conducting experiments very near to the glass transition temperature. The elastic behavior at the beginning of the imprint is simulated for different pattern sizes and thus different aspect ratios of the stamp. The investigations show, that a reduction of temperature has to be compensated by an increased imprint time and this time increase has to consider the reduction of viscosity on the one hand and the extension of the polymer flow time constants on the other hand. The experiments are suitable to define a lower limit for utilization of shear thinning effects.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Vinyl ether formulations for step and flash imprint lithography

E. K. Kim, M. D. Stewart, K. Wu, F. L. Palmieri, M. D. Dickey, J. G. Ekerdt, and C. G. Willson

J. Vac. Sci. Technol. B 23, 2967 (2005); http://dx.doi.org/10.1116/1.2131881 (5 pages) | Cited 10 times

Online Publication Date: 2 December 2005

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Acrylates have been used as patterning monomers in step and flash imprint lithography. Vinyl ether formulations have a lower viscosity, faster curing rate, and higher tensile strength than acrylate formulations. However, the lack of commercially available, silicon-containing vinyl ether monomers has required the synthesis of several new vinyl ethers. An ideal monomer has low viscosity and low vapor pressure. The vapor pressure of silicon-containing vinyl ethers was predicted using the Joback-Reid, Lyderson, and Lee-Kesler methods. BVMDSO (1,1,3,3-tetramethyl-1,3-bis(vinyloxymethyl)-disiloxane) has the lowest viscosity of the synthesized silicon-containing vinyl ethers that meet the volatility requirement for a 80 pl dispense volume. The formulation of BVMDSO, CHDVE (cyclohexanedimethanol divinyl ether), and TEGDVE (triethylene glycol divinyl ether) shows good tensile strength and modulus. The formulation of BVMDSO, CHDVE, TEGDVE, and fluorinated acetate can print a 30 nm line because it has a low separation force and high tensile modulus.
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66.20.-d Viscosity of liquids; diffusive momentum transport
62.10.+s Mechanical properties of liquids
85.40.Hp Lithography, masks and pattern transfer
back to top Nanostructures for Biology

Fabrication and surface chemistry of nanoscale bioarrays designed for the study of cytoskeletal protein binding interactions and their effect on cell motility

O. Cherniavskaya, C. J. Chen, E. Heller, E. Sun, J. Provezano, L. Kam, J. Hone, M. P. Sheetz, and S. J. Wind

J. Vac. Sci. Technol. B 23, 2972 (2005); http://dx.doi.org/10.1116/1.2132332 (7 pages) | Cited 6 times

Online Publication Date: 5 December 2005

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We have designed a system engineered to mimic biological spatial order. The system consists of nanoscale dots organized into hierarchical arrays in which structural parameters, such as spacing and orientation, are systematically varied. These arrays are used to probe the spatial distributions of binding sites in biomolecules. In this paper, we describe the fabrication process, including lithography and biofunctionalization, and we discuss issues related to surface chemistry that are critical to creating robust, biologically active nanoarrays.
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87.80.-y Biophysical techniques (research methods)
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
87.14.E- Proteins
87.15.B- Structure of biomolecules
87.17.Jj Cell locomotion, chemotaxis

Arrays of high-Q high stability ultrahigh-frequency resonators for chemical/biological sensors

R. L. Kubena, D. T. Chang, F. P. Stratton, Richard J. Joyce, T. Y. Hsu, M. K. Lim, and R. T. M’Closkey

J. Vac. Sci. Technol. B 23, 2979 (2005); http://dx.doi.org/10.1116/1.2121731 (5 pages) | Cited 3 times

Online Publication Date: 5 December 2005

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The use of nanomechanical resonators for chemical and bioagent detection has attracted a large amount of interest in recent years, since the mass noise floor scales directly with the mass of the resonator for a given frequency stability. In order for this technology to be applied to hand-held units, the resonators should ideally be integrated with the oscillator and counter electronics, have high-Q and high frequency stability in air, and have low-temperature sensitivity. We present a quartz-based ultrahigh-frequency resonator/oscillator technology that addresses these important issues. Miniaturized shear-mode resonators with frequencies approaching 3 GHz and f×Q products of >1.0×1013 Hz have been fabricated on Si using low-temperature wafer bonding and deep reactive ion quartz etching. Allan deviation levels of 1.0×10−8 for 100 s integration times have been measured for a 326 MHz Pierce oscillator design. In addition, the temperature stability matches that expected for AT-cut crystal resonators. We present preliminary selective deposition results that indicate that arrays of these oscillators could be used for highly selective and high sensitivity low-cost sensors.
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77.65.Fs Electromechanical resonance; quartz resonators
81.65.Cf Surface cleaning, etching, patterning

Effects of nanoimprinted patterns in tissue-culture polystyrene on cell behavior

W. Hu, E. K. F. Yim, R. M. Reano, K. W. Leong, and S. W. Pang

J. Vac. Sci. Technol. B 23, 2984 (2005); http://dx.doi.org/10.1116/1.2121729 (6 pages) | Cited 21 times

Online Publication Date: 5 December 2005

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Tissue engineering seeks to develop functional tissues in a biomimetic environment in vitro. As the extracellular environment in vivo is composed of numerous nanostructures, fabrication of nanostructured substrates will be valuable for tissue engineering applications. In this article, we report a simple nanoimprint lithography (NIL) process to pattern nanostructures directly on tissue-culture polystyrene plates. By repeating this NIL process, three-dimensional scaffolds consisting of multiple-layer nanostructures were also fabricated. Bovine pulmonary artery smooth muscle cells were cultured on imprinted gratings ranging from 350 nm to 10 μm. The smooth muscle cells attached and proliferated well on these imprinted substrates without additional surface treatment. Cell elongation and alignment were observed on the micro- and nanopatterns, with the effect significantly more pronounced on the nanostructures.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.85.Lf Tissue engineering
87.17.-d Cell processes
81.16.Nd Micro- and nanolithography
87.85.J- Biomaterials

Three-dimensional digital scanner based on micromachined micromirror for the metrological measurement of the human ear canal

M. Prasciolu, R. Malureanu, S. Cabrini, D. Cojoc, L. Businaro, A. Carpentiero, R. Kumar, and E. Di Fabrizio

J. Vac. Sci. Technol. B 23, 2990 (2005); http://dx.doi.org/10.1116/1.2121734 (5 pages)

Online Publication Date: 5 December 2005

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Manufacturers of hearing aids have made initial testing of rapid prototyping of hearing aid shells using laser scans of ear impressions, but they have not performed any actual scans of the human ear canal. We report the direct scanning of the human external auditory canal by using an electromagnetically actuated torsion micromirror fabricated by using a micromachining technique as the scanner. This demonstrates the actual scanning of the human external auditory canal by a single integral microelectro-optical-mechanical system (MEOMS). A prototype three-dimensional (3D) scanning system was developed: It is based on the acquisition of optical range data by a conoscopic holographic laser interferometer using an electromagnetically actuated scanning MEOMS micromirror. A fabrication process, based on a poly(methylmethacrylate) sacrificial layer for the fabrication of a free-standing micromirror was used. Micromirror actuation was achieved by using a magnetic field generated with an electromagnetic coil stick. The micromirror and electromagnet coil assembly compose the opto-mechanical scanning probe used for entering the auditory canal. Based on an actual scan map, a 3D reconstructed digital model of the ear canal was built using a surface point distribution approach. The prototype system allows a no-invasive 3D imaging of the ear canal with spatial resolution in the 10 μm range. Fabrication of two complete hearing aids from in vivo ear canal scanning is also accomplished.
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87.63.L- Visual imaging
42.40.Kw Holographic interferometry; other holographic techniques
42.62.Be Biological and medical applications
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
43.66.Ts Auditory prostheses, hearing aids
42.79.Bh Lenses, prisms and mirrors
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Va Micromachining

Sealed three-dimensional nanochannels

R. M. Reano and S. W. Pang

J. Vac. Sci. Technol. B 23, 2995 (2005); http://dx.doi.org/10.1116/1.2121728 (5 pages) | Cited 6 times

Online Publication Date: 5 December 2005

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A technique to create sealed three-dimensional nanochannel networks is developed using sequentially stacked thermal nanoimprint lithography on planarized self-supporting dielectric sealing material over polymer sacrificial layers. Void-free plasma enhanced chemical vapor deposited SiO2 encloses and seals nanochannels that are formed upon the removal of the sacrificial polymer. Planarization of the SiO2 surface allows the utilization of the vertical dimension to sequentially apply nanoimprint lithography for the formation of multiple-level nanochannel networks. Removal of the sacrificial polymer is performed with a high-power and high-pressure O2 plasma. Wet chemical processes using common solvents are found to be ineffective in removing the sacrificial polymer. Two level nanochannels with cross-sectional dimensions of 300 nm×200 nm and lengths of 65 μm that are aligned offset from one another and aligned on top of one another are demonstrated.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.65.-b Surface treatments
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
52.77.Dq Plasma-based ion implantation and deposition

Self-aligned platinum-silicide nanowires for biomolecule sensing

Fu-Hsiang Ko, Zen-Hou Yeh, Chun-Chi Chen, and Tzeng-Feng Liu

J. Vac. Sci. Technol. B 23, 3000 (2005); http://dx.doi.org/10.1116/1.2090967 (6 pages) | Cited 4 times

Online Publication Date: 5 December 2005

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A self-aligned platinum-silicide nanowire for biomolecule sensing is developed in this work. The 40 nm nanowire is fabricated through a sequence of electron-beam writing on the polysilicon film, line shrinkage with alkaline solution, platinum film deposition, 550 °C annealing, and aqua regia dissolution. The immobilization of single-stranded capture DNA onto the platinum-silicide nanowire is verified from the fluorescence-labeled technique. The field-effect transistor can distinguish the complementary, mismatched, and denatured DNA via the conductance difference. Although the nanowire sensor has not been integrated into a fluid channel system, we can sense the minimal target DNA concentration down to 100 fM, and the signal is still 1000-fold larger than the noise signal.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.14.G- Nucleic acids
85.30.Tv Field effect devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Resonant grating filters as refractive index sensors for chemical and biological detections

Jian Jim Wang, Lei Chen, Steven Kwan, Feng Liu, and Xuegong Deng

J. Vac. Sci. Technol. B 23, 3006 (2005); http://dx.doi.org/10.1116/1.2101774 (5 pages) | Cited 12 times

Online Publication Date: 5 December 2005

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A chemical and biological sensor based on a free-space waveguide resonant grating optical filter has been developed. Different from the conventional surface plasmon resonance sensors and the conventional waveguide mode sensors, which require either prism coupling or grating coupling, the proposed free-space optical sensor device does not require special separate coupling. The inherent 100% coupling efficiency at resonance can significantly boost probe efficiency. Both simulation and experimental results have demonstrated that the sensor could deliver a resolution of better than 0.001–0.0001 for refractive index sensing, which is enough for detecting various chemical and biological materials. More importantly, under an angular detection scheme, the proposed waveguide resonant grating sensor could be one order’s more sensitive than the conventional surface plasmon resonance sensor.
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82.80.-d Chemical analysis and related physical methods of analysis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Ci Filters, zone plates, and polarizers
42.79.Gn Optical waveguides and couplers

Polymer cell culture substrates with combined nanotopographical patterns and micropatterned chemical domains

Joseph L. Charest, Marcus T. Eliason, Andrés J. García, William P. King, A. Alec Talin, and Blake A. Simmons

J. Vac. Sci. Technol. B 23, 3011 (2005); http://dx.doi.org/10.1116/1.2127951 (4 pages) | Cited 17 times

Online Publication Date: 5 December 2005

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A combination of nanoimprint lithography and microcontact printing was used to create cell substrates with well-defined nanotopographic patterns of grooves overlaid with independently controlled micropatterned chemical domains. Qualitative analysis of osteoblast-like cells cultured on the substrates showed alignment of cells and cell features to the nanotopographic grooves when surface chemistry was either uniform or a pattern of dots. When surface chemistry on the substrate was a pattern of lanes, cells aligned to the lanes. On all substrates, small cellular extensions, or filopodia, displayed no particular alignment to either nanotopographic grooves or chemical patterns. Large cell extensions were observed only parallel to either nanotopographic grooves or chemical lanes. The techniques used provide an easily scaleable approach to creating cell substrates that will aid in studying the relative impact and interplay of chemical patterns and mechanical topography on cellular responses.
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87.85.J- Biomaterials
87.85.Lf Tissue engineering
87.17.-d Cell processes
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
87.15.N- Properties of solutions of macromolecules
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
back to top Metrology, Alignment, and CD Control

Advanced electron microscopy needs for nanotechnology and nanomanufacturing

Michael T. Postek, John S. Villarrubia, and András E. Vladár

J. Vac. Sci. Technol. B 23, 3015 (2005); http://dx.doi.org/10.1116/1.2135795 (8 pages) | Cited 3 times

Online Publication Date: 6 December 2005

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Advances in fundamental nanoscience, design of nanomaterials, and ultimately manufacturing of nanometer scale products all depend to some degree on the capability to accurately and reproducibly measure dimensions, properties, and performance characteristics at the nanoscale. Measurement tools and techniques are needed to image and measure in this realm of research, development, and technology. Currently available metrology tools are also beginning to reach the limits of resolution and accuracy and are not expected to meet future requirements for nanotechnology or nanomanufacturing. Clever approaches to this problem need to be developed. Further, even with the vast array of current tools available, the important question is whether or not they are providing the needed information. Revolutionary approaches to the metrology may be required in the near future. This article discusses some of the issues and potential solutions being undertaken in the scanning electron microscope dimensional metrology project at the National Institute of Standards and Technology.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.16.-c Methods of micro- and nanofabrication and processing

Effect of initial resist thickness on residual layer thickness of nanoimprinted structures

Hae-Jeong Lee, Hyun Wook Ro, Christopher L. Soles, Ronald L. Jones, Eric K. Lin, Wen-li Wu, and D. R. Hines

J. Vac. Sci. Technol. B 23, 3023 (2005); http://dx.doi.org/10.1116/1.2101776 (5 pages) | Cited 15 times

Online Publication Date: 6 December 2005

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Quantification and control of the residual layer thickness is a critical challenge facing nanoimprint lithography. This thickness must be known to within a few nanometers, yet there are very few nondestructive measurement techniques capable of extracting such information. Here we describe a specular x-ray reflectivity technique that can be used to not only quantify the thickness of the residual layer with sub-nm resolution, but also to extract the pattern height, the line-to-space ratio, and relative linewidth variations as a function of the pattern height. This is illustrated through a series of imprints where the initial film thickness is varied. For films with sufficient resist material to fill the mold, complete pattern filling is observed and the residual layer thickness is directly proportional to the initial film thickness. When there is insufficient resist material in the film to completely fill the patterns in the mold, a finite residual layer thickness of approximately 50–100 Å is still observed.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.70.-q Methods of materials testing and analysis

Traceable calibration of critical-dimension atomic force microscope linewidth measurements with nanometer uncertainty

R. G. Dixson, R. A. Allen, W. F. Guthrie, and M. W. Cresswell

J. Vac. Sci. Technol. B 23, 3028 (2005); http://dx.doi.org/10.1116/1.2130347 (5 pages) | Cited 22 times

Online Publication Date: 6 December 2005

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The use of critical dimension atomic force microscopes (CD AFMs) in semiconductor manufacturing, both for process control and as a reference metrology tool, is increasing. If the tip width is calibrated consistently between measurements, a CD AFM can function as an excellent width comparator. Relative widths can be measured with uncertainties of 1 nm or less. However, to perform accurate measurements, the absolute tip width must be accurately calibrated. Until recently, conventional methods for accomplishing this had standard uncertainties on the order of 5 nm. Recently developed CD reference materials now make it possible to calibrate absolute tip width with uncertainties at the 1 nm level. The highlights of our method are: (1) the use of single-crystal silicon and preferential etching to pattern well-defined and highly uniform features; (2) the use of high resolution transmission electron microscopy (HRTEM) to access the Si lattice spacing directly as a source of traceable width information, and (3) the use of CD AFM to transfer width information from the HRTEM samples. These standards are known as single crystal critical dimension reference materials (SCCDRM), and prototype SCCDRMs have recently been delivered to SEMATECH Member Companies for evaluation.
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07.79.Lh Atomic force microscopes
06.20.Dk Measurement and error theory

Local critical dimension variation from shot-noise related line edge roughness

P. Kruit and S. Steenbrink

J. Vac. Sci. Technol. B 23, 3033 (2005); http://dx.doi.org/10.1116/1.2127941 (4 pages) | Cited 20 times

Online Publication Date: 6 December 2005

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Shot noise effects are important to take into account both in the design of resists for lithography and in the design of lithography tools. The statistics of electron or photon arrival gives rise to dose variations, which translate to variations in the size of written features. It is possible to model the shot noise effects in an analytical equation, which shows the influence of all relevant parameters. The sequence of subsequent events in the resist: Secondary electron creation, acid generation, and acid diffusion are incorporated in the model. The model then allows the evaluation of the minimum resist sensitivity necessary for a certain required critical dimension control.
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85.40.Hp Lithography, masks and pattern transfer

Subpixel alignment for scanning-beam lithography using one-dimensional, phase-based mark detection

A. V. Krishnamurthy, R. V. Namepalli, and J. T. Hastings

J. Vac. Sci. Technol. B 23, 3037 (2005); http://dx.doi.org/10.1116/1.2062547 (6 pages) | Cited 4 times

Online Publication Date: 6 December 2005

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A phase-based alignment technique for scanning electron-beam lithography is proposed and evaluated. The approach uses a grid alignment mark rotated with respect to the beam deflection axes and requires only a single, one-dimensional (1D) line scan to perform subpixel registration in both the x and y directions. This 1D, phase-based method promises subpixel alignment without interpolation, faster mark signal acquisition, and more computationally efficient detection. Theoretical limits for alignment accuracy and a simple phase-estimation algorithm that approaches these limits are described. Monte Carlo simulations indicate that nanometer-level registration precision can be achieved with modest grid periods and signal to noise ratios (SNRs). Experimental measurements of registration variance as a function of SNR agree well with both theory and simulation. Registration errors of 3 nm (1-standard deviation) are observed using a 1 μm grid period, 49 nm pixel size, and the highest observed SNR of 5.9.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Investigation of overlay errors due to the interaction of optical and extreme ultraviolet mask fabrication processes

L. Zheng, R. L. Engelstad, and E. G. Lovell

J. Vac. Sci. Technol. B 23, 3043 (2005); http://dx.doi.org/10.1116/1.2127949 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2005

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Overlay tolerances are becoming increasingly severe as lithography technology drives the minimum integrated-circuit feature size below 65 nm. Manufacturable solutions at the lower nodes are essentially unknown. The goal of this article is to investigate overlay errors at the 45-nm node, for a mix-and-match of optical and extreme ultraviolet (EUV) lithographies. In particular, image placement errors induced during mask fabrication are predicted for a specified test pattern, which includes the possibility of having individual layers on the device wafer patterned by either optical or EUV lithographic processes. Finite element (FE) models have been developed to simulate the response of both optical and EUV masks during fabrication and chucking. In order to track image placement errors of the actual features within the pattern area, submodeling techniques were developed for the FE simulations. In addition, equivalent material properties were determined for the individual patterns used for the different optical and EUV masks. The FE simulations clearly indicate that the most significant source of overlay error is the fabrication of the optical reticle, primarily due to differences in chucking of the mask during e-beam patterning and exposure. Modeling results are being used by the industry to establish guidelines for reticle chucking and fabrication standards.
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85.40.Hp Lithography, masks and pattern transfer

Overlay alignment using optical microscopy and arbitrary surface features

Carl Picciotto, Jun Gao, Eric Hoarau, Wei Wu, Warren Jackson, and William M. Tong

J. Vac. Sci. Technol. B 23, 3047 (2005); http://dx.doi.org/10.1116/1.2062667 (5 pages) | Cited 2 times

Online Publication Date: 6 December 2005

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In this article, we present our nanoscale displacement sensing and estimation (nDSE) theory,which describes the theoretical limitations of displacement-sensing and predicts thepracticality of measuring nanoscale displacements using optical microscopy, and indirect displacement-measurement-based alignment (IDMA), an application framework for achieving precision alignment using individual displacement sensing rather than directly comparing nominally identical alignment marks. We propose that IDMA may form the basis for low-cost overlay alignment metrology for emerging fabrication techniques such as nanoimprint lithography. As a first step in experimentally investigating IDMA on a nanoimprinting tool, we present a variation, direct displacement-measurement-based alignment (DDMA), and we describe proof-of-concept experiments performed using an in-house nanoimprinter. We demonstrate that DDMA, enabled by nDSE, can measure misalignments in the tens of microns to a precision easily better than 100 nm. We maintain that in more optimized conditions DDMA should be expected to provide precisions in the 20 nm range. More to the point, we expect that IDMA, the preferred application framework, will demonstrate even better results due to its inherent robustness against mismatched alignment targets, an inevitable issue faced in real-world application environments. For more background information please see the work presented by J. Gao, C. Picciotto, and W. Jackson [Appl. Phys. A 80, 1265 (2005) ] and C. Picciotto, J. Gao, E. Hoarau, and W. Wu [Appl. Phys. A 80, 1287 (2005) ].
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81.16.Nd Micro- and nanolithography
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Technique for estimating the angle of incidence and depth of focus of an electron beam

Fumio Mizuno, Isao Amemiya, and Kazutake Taniguchi

J. Vac. Sci. Technol. B 23, 3052 (2005); http://dx.doi.org/10.1116/1.2127947 (4 pages)

Online Publication Date: 6 December 2005

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In order to cope with the problems with scanning electron microscopes for semiconductor manufacturing, the ability to measure the focal depth and incident angle of an electron beam is required. A technique for estimating the angle of incidence and the depth of focus has been devised. The main feature of the technique is to employ the specimen with a special pit, which is formed from sidewalls with an accurate tilt angle and a surface structure. In this work, the pit was formed on a (100) silicon-crystal substrate and from four (111) sidewalls with an accurate tilt angle of 54.74° and a step-like surface. The incident angle and focal depth of an electron beam was estimated by using the pit. The estimation result agreed approximately with the expected.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Portable coordinate measuring tool

Li Jiang and M. Feldman

J. Vac. Sci. Technol. B 23, 3056 (2005); http://dx.doi.org/10.1116/1.2134718 (5 pages) | Cited 4 times

Online Publication Date: 6 December 2005

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The ability to accurately measure the placement of features within a level is becoming increasingly critical in integrated circuit fabrication. In this article the level to be measured is patterned on a transparent wafer in poly(methylmethacrylate) (PMMA) resist to which a blue absorbing dye has been added. The dyed resist is on top of a thin partially transparent aluminum layer and is highly visible when viewed in reflected blue light in an oil immersion microscope. It is placed over a diffraction grating, which is not visible, both because the aluminum layer reflects most of the light and because the grating is far out of focus. In transmitted red laser light the grating can be seen, since various techniques may be used to increase the depth of focus of gratings in collimated monochromatic light. However, the resist pattern is not seen, because the resist is transparent to red light and the immersion oil matches its index of refraction. Measuring the separation between features reduces to measuring their location with respect to individual grating lines, and then counting the number of lines between them. The image placement accuracy of levels measured with two-dimensional gratings will be limited by the accuracy of the gratings—at present less than 2 nm.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
42.79.Dj Gratings

Fabrication of high-secondary-electron-yield grids for spatial-phase-locked electron-beam lithography

Feng Zhang, Henry I. Smith, and Jianfeng Dai

J. Vac. Sci. Technol. B 23, 3061 (2005); http://dx.doi.org/10.1116/1.2110341 (4 pages) | Cited 4 times

Online Publication Date: 6 December 2005

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Poor placement accuracy is a major issue and inhibitor in all forms of electron-beam lithography (EBL), a direct result of the open-loop nature of EBL. In scanning-electron-beam lithography (SEBL), the beam position is not continuously monitored during exposure. Instead, one depends upon a laser-interferometer-controlled stage and secondary referencing. In SEBL, the beam can deviate from its intended position causing pattern-placement errors that are often worse than the resolution. Spatial-phase-locked electron-beam lithography (SPLEBL) is being developed at MIT to achieve nanometer-level absolute placement accuracy. In its global-fiducial-grid mode, SPLEBL directly references the beam location to an electron-transparent grid, placed on top of the e-beam resist, during exposure. Recently pattern-placement precision of ∼ 1 nm was demonstrated with secondary electrons as the reference signal [ J. T. Hastings, F. Zhang, and H. I. Smith, J. Vac. Sci. Technol. B 21, 2650 (2003) ]. However, the fabrication process used for the reference grid was complex and would not be acceptable in manufacturing. In this article, we describe a process for putting down the grid that is user friendly and preserves its long-range spatial-phase coherence. We also investigated a variety of candidate grid materials (various low-Z metals and C60) for their secondary-electron yields and processibility.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Pattern matching between a scanning electron microscopy exposed pattern image of large-scale integrated fine structures and computer-aided design layout data by using the relaxation method

K. Miura, M. Fujita, K. Nakamae, and H. Fujioka

J. Vac. Sci. Technol. B 23, 3065 (2005); http://dx.doi.org/10.1116/1.2131877 (4 pages) | Cited 1 time

Online Publication Date: 6 December 2005

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A pattern matching technique between a scanning electron microscopy (SEM) exposed pattern image of large-scale integrated fine structures and computer-aided design (CAD) layout data based on the relaxation method is proposed wherein circular arc components are utilized. Edges are extracted from the SEM image and corners in the CAD layout are rounded. The edges in the SEM and CAD layout images are divided into three components: horizontal and vertical straight-line segments, and circular arcs. These components are expressed by bounding boxes; the optimal combination between the SEM and CAD components is then searched by using the probabilistic relaxation method. The mean vector among the obtained shift vectors shows the matching point. We applied our method to SEM exposed pattern images and compared the results with those of the conventional cross-correlation method. The results showed that our method has good robustness against change in shape of exposed pattern. The computation time of our method was comparable to the cross-correlation method.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Measurement of residual thickness using scatterometry

David Fuard, Corinne Perret, Vincent Farys, Cécile Gourgon, and Patrick Schiavone

J. Vac. Sci. Technol. B 23, 3069 (2005); http://dx.doi.org/10.1116/1.2130345 (6 pages) | Cited 7 times

Online Publication Date: 6 December 2005

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Nanoimprint lithography (NIL) processes have the characteristic that a residual resist layer is always present between the nanoimprinted features. This residual resist layer must be removed to obtain usable resist masks for pattern transfer. As this resist layer is removed using oxygen-based plasma processes, the residual thickness nonuniformity translates into feature width dispersion. Thus, the uniformity of this residual thickness after imprint remains an important issue for nanoimprint lithography and a reliable metrology procedure is required for. At present, the standard measurement method is based on scanning electron microscopy (SEM) cross section, which is destructive, time consuming, and may sometimes provide only moderate accuracy. The work presented here will assess and show the interest of scatterometry, which is a nondestructive optical method of metrology that can be easily applied to NIL. This measurement procedure exhibits very good accuracy on the two-dimensional-feature geometry determination, especially for residual thickness. Scatterometry also eases time-consuming studies like residual thickness measurement at the local scale or at the wafer scale. Moreover, this article shows that the imprint uniformity studies provide very interesting information on the mold deformation.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
81.16.Nd Micro- and nanolithography
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Line edge roughness characterization with a three-dimensional atomic force microscope: Transfer during gate patterning processes

J. Thiault, J. Foucher, J. H. Tortai, O. Joubert, S. Landis, and S. Pauliac

J. Vac. Sci. Technol. B 23, 3075 (2005); http://dx.doi.org/10.1116/1.2101789 (5 pages) | Cited 12 times

Online Publication Date: 6 December 2005

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As critical dimensions (CD) for semiconductor devices shrink to a few tens of nanometers, the line edge roughness (LER) and linewidth roughness (LWR) becomes a critical issue. For this study, we used a new 3D CD-AFM which enables us to characterize LER and LWR along the features after each technological step of standard gate patterning processes. Isolated lines with CDs going from 20 nm and 100 nm were written with an e-beam lithography tool. First, we transfer the resist mask into silicon to determine the influence of different plasma chemistries on LER. Then, the resist mask is transferred into a standard CMOS gate stack: SiO2 hard mask, polysilicon, dielectric gate. The results after e-beam lithography show that the LWR measured at the bottom of the pattern is higher than the one measured at the middle. It can be attributed to the effect of backscattered electrons. Then, we show that for smaller dimensions, the trimming that occurs during the hard mask opening process weakens the resist and increases drastically the LWR in the polysilicon. This puts forward one limitation of standard processes for aggressive gate patterning. Finally, we do not observe any obvious trend on LER and LWR after the characterization of features coming from two different silicon etching chemistries. This conclusion is surprising. We attributed it to the tip size limitation in sidewall roughness detection on silicon.
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81.16.Ta Atom manipulation
68.37.Ps Atomic force microscopy (AFM)
81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Reconstruction of pattern images from scanning electron microscope images

Hanying Feng, Jun Ye, and R. Fabian W. Pease

J. Vac. Sci. Technol. B 23, 3080 (2005); http://dx.doi.org/10.1116/1.2127944 (5 pages) | Cited 1 time

Online Publication Date: 6 December 2005

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As the characteristic feature sizes of integrated circuits continue to shrink, both research and manufacturing are increasingly reliant on the scanning electron microscope (SEM) images. In this article, we propose a robust algorithm that automatically extracts the full edge contours from the SEM images and then converts the SEM images to pattern images even when the SEM images are corrupted by strong noise and lossy compression. This algorithm is expected to have many applications. An example of application—defect self-inspection—based on SEM conversion using this algorithm, is also shown.
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42.30.Wb Image reconstruction; tomography
42.30.Sy Pattern recognition

Self inspection of integrated circuits pattern defects using support vector machines

Hanying Feng, Jun Ye, and R. Fabian Pease

J. Vac. Sci. Technol. B 23, 3085 (2005); http://dx.doi.org/10.1116/1.2062434 (5 pages) | Cited 2 times

Online Publication Date: 6 December 2005

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At various steps of integrated circuit manufacturing, defects need to be inspected to ensure process integrity. It is desirable to detect the defects based on the captured optical image itself without comparing to any reference image. Such a methodology of defect inspection without any reference image is called defect self inspection. In this article, we investigate the defect self inspection using the support vector machines, a pattern classification methodology, and present detection sensitivity of this approach.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Advanced atomic force microscopy probes: Wear resistant designs

H. Liu, M. Klonowski, D. Kneeburg, G. Dahlen, M. Osborn, and T. Bao

J. Vac. Sci. Technol. B 23, 3090 (2005); http://dx.doi.org/10.1116/1.2127936 (4 pages) | Cited 11 times

Online Publication Date: 6 December 2005

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Tip [in this article, tip refers to the apex region of an atomic force microscopy (AFM) probe. A probe consists of substrate, cantilever, and tip.] wear is a phenomenon that can reduce the accuracy and reliability of AFM. As both tip size and specimen approach nanometer scale, tip shape change due to wear becomes critical to topographical measurements such as critical dimensions and deep trenches. This article presents probe designs with specific wear-resistant features. Three categories of probe modification were selected to lessen wear, thereby improving lifetime and performance. These are probe material, surface coatings, and selective shape.
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07.79.Lh Atomic force microscopes
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.65.-b Surface treatments

Improving critical dimension accuracy and throughput by subfield scheduling in electron beam mask writing

Sergey Babin, Andrew B. Kahng, Ion I. Măndoiu, and Swamy Muddu

J. Vac. Sci. Technol. B 23, 3094 (2005); http://dx.doi.org/10.1116/1.2132330 (7 pages) | Cited 1 time

Online Publication Date: 6 December 2005

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Resist heating in high-voltage, high-throughput electron beam (e-beam) mask write is a significant source of critical dimension (CD) distortion. Excessive heating on the reticle determines changes in resist sensitivity, which in turn cause significant CD variation. CD distortions on the reticle are replicated onto the wafer with increased magnitude as determined by the mask error enhancement factor (MEEF). As designs enter the sub-90 nm regime, CD variation has a significant impact on performance, performance variation, and product yield. Previous methods for reducing CD distortion include usage of lower e-beam current density, increased delays between electron flashes, and multipass writing. However, all of these methods lower mask writing throughput, which is increasingly becoming a limiting factor in semiconductor industry productivity. In this paper, we propose a novel method for minimizing CD distortion and maximizing mask writing throughput. By scheduling the writing of subfields, we perform simultaneous optimization of mask writing order and e-beam current density. We perform subfield scheduling by evaluating resist temperature of subfield orderings using a fast analytical temperature model. Simulation experiments show that the new subfield scheduling method can reduce the maximum resist temperature up to 12 °C over existing sequential writing methods with unchanged mask writing throughput. Alternatively, improved subfield scheduling can enable the use of higher beam current densities, leading to increased writing throughput without compromising CD control.
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85.40.Hp Lithography, masks and pattern transfer
back to top Mask Making Technology

Advanced photolithographic mask repair using electron beams

Ted Liang, Eric Frendberg, Barry Lieberman, and Alan Stivers

J. Vac. Sci. Technol. B 23, 3101 (2005); http://dx.doi.org/10.1116/1.2062428 (5 pages) | Cited 18 times

Online Publication Date: 6 December 2005

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Mask repair plays an important role in yielding advanced masks that support the lithography roadmap. It is also one of the more challenging parts of mask fabrication. Electron beam induced deposition and etching have shown great potential for mask repair applications. Our work has demonstrated that e-beam mask repair provides the superior resolution and damage-free process that is needed to support mask generations for the 32 nm technology node and beyond. This article describes an installed e-beam mask repair tool at Intel Mask Operation and discusses the capabilities of this enabling technology based on results obtained from repairing masks with “defects” intentionally inserted into the design (programmed defect masks). Specifically, results are presented for quartz etch repair of alternating phase shift masks and TaBN absorber etch of extreme ultraviolet masks, two of the most difficult types of mask to repair using conventional methods.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Electromagnetic phenomena in advanced photomasks

F. M. Schellenberg, K. Adam, J. Matteo, and L. Hesselink

J. Vac. Sci. Technol. B 23, 3106 (2005); http://dx.doi.org/10.1116/1.2110281 (10 pages) | Cited 2 times

Online Publication Date: 6 December 2005

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The adoption of resolution enhancement techniques (RET) for subwavelength lithography relies on performing accurate simulation of mask effects. Although topography effects have been successfully used in RET flows, the impact of electromagnetic effects such as surface plasmons tend to be ignored. It is known, however, from the performance of “C-shaped” apertures that extraordinary transmission and opacity can be achieved using these electromagnetic effects. We have examined simulations for representative 45 nm features using both conventional and novel finite difference time domain simulators. When the mask material is assumed to be conducting chromium, we found that electromagnetic effects appear to be significant and highly dependent on polarization. This may place additional constraints on the specification of mask material composition for these integrated circuit generations.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
back to top Etching and Deposition for the Nanometer Era

Innovative approach to nanoscale device fabrication and low-temperature nitride film growth

Elshan A. Akhadov, D. E. Read, Alexander H. Mueller, Jacqueline Murray, and Mark A. Hoffbauer

J. Vac. Sci. Technol. B 23, 3116 (2005); http://dx.doi.org/10.1116/1.2130346 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2005

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Energetic neutral beam lithography/epitaxy (ENABLE) was used for etching very high-aspect-ratio nanoscale structures into polymers and for growing templated AlN films at low temperatures. Various methods were used for masking polymeric films for selective etching by energetic oxygen atoms to fabricate sub-100 nm structures with aspect ratios exceeding 35:1. ENABLE was also utilized for low-temperature growth of AlN into previously etched polymer templates to directly form AlN wires. By taking advantage of the unique processing capabilities of ENABLE, new opportunities for making delicate nanostructures are made possible.
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81.16.Nd Micro- and nanolithography
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
85.35.-p Nanoelectronic devices
81.65.Cf Surface cleaning, etching, patterning

Electron beam lithography patterning of sub-10 nm line using hydrogen silsesquioxane for nanoscale device applications

In-Bok Baek, Jong-Heon Yang, Won-Ju Cho, Chang-Geun Ahn, Kiju Im, and Seongjae Lee

J. Vac. Sci. Technol. B 23, 3120 (2005); http://dx.doi.org/10.1116/1.2132328 (4 pages) | Cited 12 times

Online Publication Date: 7 December 2005

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We investigated novel patterning techniques to produce ultrafine patterns for nanoscale devices. Hydrogen silsesquioxane (HSQ) was employed as a high-resolution negative tone inorganic electron beam resist. The nanoscale patterns with sub-10 nm linewidth were successfully formed. A trimming process of HSQ by the reactive ion etcher (RIE) played an important role for the formation of 5 nm nanowire patterns. Additionally, hybrid lithography was used to produce various device patterns as well as to minimize proximity effects of electron beam lithography (EBL). Finally, we successfully fabricated triple-gate metal oxide semiconductor field effect transistor (MOSFET) with a gate length of 6 nm by using the proposed patterning process.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
85.30.Tv Field effect devices

Direct-write e-beam patterning of stimuli-responsive hydrogel nanostructures

Vijay R. Tirumala, Ralu Divan, Leonidas E. Ocola, and Derrick C. Mancini

J. Vac. Sci. Technol. B 23, 3124 (2005); http://dx.doi.org/10.1116/1.2062649 (5 pages) | Cited 15 times

Online Publication Date: 7 December 2005

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The need for stimuli-responsive components in microfluidic systems has led to the development of hydrogel-based patterned microstructures. The most commonly practiced means for fabricating micropatterned hydrogels is based on in situ photopolymerization using 365 nm UV light in a liquid medium. This approach has been found to be very successful for patterning hydrogel-based features with tens or hundreds of microns resolution, but its main drawback lies in having to contain the liquid prepolymer mixture within the device for irradiation. We instead propose an alternate approach that uses direct-write electron-beam radiation to cross-link a dry, spin-coated thin film of linear polymer. After exposure, the linear polymer is dissolved in water leaving behind the cross-linked regions. When immersed in water, the cross-linked regions assume the properties of hydrogel and undergo naturally thermoreversible swelling and shrinking. This direct-writing approach can be used to fabricate hydrogel-based nanostructures down to 100 nm linewidth and also is amenable to easy integration into nano and bio devices. We focus on patterning a well-known thermoreversible hydrogel, poly (N-isopropylacrylamide), and use it to discuss various aspects of process methodology, fabrication, characterization, and stimuli-response properties of nanosized hydrogels in detail.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
82.70.Gg Gels and sols
82.35.-x Polymers: properties; reactions; polymerization

Reduction of oxide layer on Ru surface by atomic-hydrogen treatment

I. Nishiyama, H. Oizumi, K. Motai, A. Izumi, T. Ueno, H. Akiyama, and A. Namiki

J. Vac. Sci. Technol. B 23, 3129 (2005); http://dx.doi.org/10.1116/1.2130356 (3 pages) | Cited 14 times

Online Publication Date: 7 December 2005

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The reduction of Ru oxide was examined as a way of cleaning the cap layer of multilayer mirrors in extreme ultraviolet lithography (EUVL). Ru deposited on a Si surface was oxidized using electron cyclotron resonance (ECR) O2 plasma, and then treated with atomic hydrogen generated with a hot tungsten wire. An analysis of the surface composition by x-ray photoelectron spectroscopy and Auger electron spectroscopy revealed that atomic hydrogen removed the Ru oxide resulting from the ECR O2 plasma treatment. Additionally, atomic force microscopy observations showed that this treatment caused no increase in the surface roughness of the Ru. This indicates that the surface oxidation of EUVL mirrors is reversible, and can largely be eliminated by using atomic hydrogen and the proper cap layer.
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81.05.Bx Metals, semimetals, and alloys
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Fv Electron impact: Auger emission
68.37.Ps Atomic force microscopy (AFM)
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.De Metallic surfaces

Nanoscale patterning in application to materials and device structures

A. Erbe, W. Jiang, Z. Bao, D. Abusch-Magder, D. M. Tennant, E. Garfunkel, and N. Zhitenev

J. Vac. Sci. Technol. B 23, 3132 (2005); http://dx.doi.org/10.1116/1.2130353 (6 pages)

Online Publication Date: 7 December 2005

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We present fabrication schemes for nanoscale molecular junctions, which allow the deposition of molecules after the fabrication steps that can uncontrollably affect the electrical properties of the molecular layers. The two techniques described here use shadow mask evaporation and nanotransfer printing. In order to make reliable contacts with the molecules (or molecular monolayers) the morphology of the contacting metals has to be optimized and controlled. We therefore characterize the surfaces of the contacting metals using scanning electron microscopy and scanning probe microscopy at various stages of the fabrication. Based on these results we developed methods to improve the morphology in order to realize more reliable metal-molecule contacts. It is shown that improvement of the surface topography of the metals indeed leads to metal-molecule-metal junctions with a very low failure rate.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Nb Molecular nanostructures
81.07.Lk Nanocontacts
85.65.+h Molecular electronic devices
81.16.Nd Micro- and nanolithography
64.70.F- Liquid-vapor transitions
73.63.Rt Nanoscale contacts
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Low damage sputter deposition of tungsten for decanano compound semiconductor transistors

X. Cao, D. S. Macintyre, S. Thoms, X. Li, H. Zhou, C. D. W. Wilkinson, M. Holland, L. Donaldson, F. McEwan, H. McLellend, and I. Thayne

J. Vac. Sci. Technol. B 23, 3138 (2005); http://dx.doi.org/10.1116/1.2127937 (5 pages)

Online Publication Date: 7 December 2005

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This article investigates sputter-induced damage caused by direct current magnetron sputter coating of tungsten on GaAs based high electron mobility transistor layer structures with channels buried less than 20 nm from the surface. Van der Pauw structures were used to study the effect of tungsten sputtering on the transport properties of these shallow channels. Using this approach we established that substrate damage can be minimized by using low sputtering currents, a large source to substrate distance, and a high sputtering pressure. Unfortunately such sputtering conditions do not produce the best quality dense films necessary for device fabrication and it was necessary to establish conditions which were a compromise of film quality and substrate damage. Postsputter annealing was found to significantly reduce the damage and a loss of 10% in semiconductor conductivity was obtained for good quality tungsten films.
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81.15.Cd Deposition by sputtering
73.61.At Metal and metallic alloys
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

Copper germanide Ohmic contact on n-type gallium nitride using silicon tetrachloride plasma

Michael L. Schuette and Wu Lu

J. Vac. Sci. Technol. B 23, 3143 (2005); http://dx.doi.org/10.1116/1.2132331 (5 pages) | Cited 3 times

Online Publication Date: 7 December 2005

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A Ge/Cu/Ge Ohmic contact scheme has been applied to moderately-doped n-GaN, showing specific contact resistivity of 1.1×10−5 Ω cm2 and contact resistance equal to 0.26 Ω mm. SiCl4 RIE at a dc self-bias of −150 V is found to reduce the GaN RMS surface roughness (Rq) from 4.6 Å to 3.2 Å while a −350 V treatment slightly increases Rq to 4.1 Å. It is demonstrated by x-ray photoelectron spectroscopy that ion bombardment of n-GaN, in conjunction with a hydrochloric acid treatment, reduces surface oxidation and increases the concentration of nitrogen vacancies (VN), a donorlike defect, at the surface. Auger electron spectroscopy depth profiling shows that a 600 °C anneal encourages interdiffusion of Ga and Ge such that the heavily-n-doped interfacial region caused by VN is further enhanced. The results therefore suggest that the Ohmic behavior of the Cu3Ge Ohmic contact on n-GaN is due to increased tunneling current at the metal/semiconductor interface caused by the creation of donor-like VN as well as Ge on VGa.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
79.20.Fv Electron impact: Auger emission
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Simulation of the cathode surface damages in a HOPFED during ion bombardment

Hongping Zhao, Wei Lei, Xiaobing Zhang, Xiaohua Li, and Qilong Wang

J. Vac. Sci. Technol. B 23, 3148 (2005); http://dx.doi.org/10.1116/1.2134720 (5 pages) | Cited 1 time

Online Publication Date: 7 December 2005

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Most vacuum devices are hampered by ion bombardment due to residual gases. Sometimes, it causes the breakdown of devices and shortens their life. In this article, the effect of the ion bombardment on the cathode surface in a structure of a field emission display was simulated. In this structure, a special type of spacer was used, named “hop” and “flu” spacer. The trajectories of electrons emitted by a cold cathode were calculated under influence of an electric field. From these calculations, the ionization of a residual gas and the corresponding trajectories of the positive ions were estimated. In this article, we modeled Si microtip and Mo microtip field emitters. Because inert gases are not easily absorbed by the getter, several different types of residual gases, such as neon, argon, krypton, and xenon, were introduced in the simulation. The simulation results show that ion bombardment damages on a silicon target induced by Ar, Kr, and Xe are more destructive than Ne. Also, Ar, Kr, and Xe are shown to be more destructive than Ne to a molybdenum microtip. The results obtained in this article suggest damage on Si is larger than that on Mo under the same ion bombardment and that a molybdenum emitter is more stable than a silicon emitter in a nonideal vacuum environment.
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85.45.Fd Field emission displays (FEDs)
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
61.82.Fk Semiconductors
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
back to top Nanodevices

Micromachined Arch-type cantilever as high sensitivity uncooled infrared detector

K. Ivanova, Tzv. Ivanov, and I. W. Rangelow

J. Vac. Sci. Technol. B 23, 3153 (2005); http://dx.doi.org/10.1116/1.2134721 (5 pages)

Online Publication Date: 7 December 2005

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In this article, we discuss an uncooled infrared (IR) detector based on an “arch-type” design realized with advanced microelectromechanical systems technology. Bimaterial microcantilevers undergo bending as their temperature changes due to the absorption of infrared photons. The bending is proportional to dissimilar thermal expansion of the two different materials composing the cantilever. We select the most optimal combination of materials used commonly in the micromachining technology resulting in highest bimaterial effect. Well known SU8 negative resist is one promising candidate having high thermal expansion coefficient (α = 52×10−6/K), and relatively low thermal conductivity (0.2 W/m K). Creating a micromechanical “arch” shaped cantilever a differential stress is induced due to different thermal expansion of middle beam formed from the SU8-film. Moreover, we fabricate a design microcantilever IR detector that consists two unique skills: (i) a Si/SU8 bimaterial system as material combination with beneficial bimaterial effect and (ii) tiny silicon “arch” shaped loop which includes two beams for piezoresistive detection of the bending.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
46.70.De Beams, plates, and shells
07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
46.35.+z Viscoelasticity, plasticity, viscoplasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
72.20.Fr Low-field transport and mobility; piezoresistance

Rapid prototyping of infrared bandpass filters using aperture array lithography

Keping Han, Mark Morgan, Ariel Ruiz, Sri C. Vemula, and Paul Ruchhoeft

J. Vac. Sci. Technol. B 23, 3158 (2005); http://dx.doi.org/10.1116/1.2062653 (6 pages) | Cited 1 time

Online Publication Date: 7 December 2005

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We demonstrate the prototyping of infrared bandpass filters, which consist of cross-shaped openings in a thin gold film, using ion beam aperture array lithography. In the lithography process, a stencil mask containing a periodic array of square apertures is irradiated by a broad beam of helium ions. The ions that pass through the openings expose the resist on a substrate that is placed in close proximity and cross-shaped filter structures are printed by moving the stage underneath the substrate, thus allowing for rapid formation of periodic patterns. We have fabricated filter patterns with peak transmittance ranging from 53% to 67% at wavelengths between 1.2 and 1.3 μm that exhibit high reflectance for longer wavelength radiation. The prototyping throughput for masks with 2 μm pitch patterns was about 2 cm2/h. The spectral performance of the prototyped filters was measured. Large-area, second-generation masks with 667 nm pitch had a lithography throughput of 300 cm2/h and were used to print filter patterns of similar quality.
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85.40.Hp Lithography, masks and pattern transfer
84.30.Vn Filters

Monolithically integrated circular polarizers with two-layer nano-gratings fabricated by imprint lithography

Jian Jim Wang, Feng Liu, Xuegong Deng, Xiaoming Liu, Lei Chen, Paul Sciortino, and Ron Varghese

J. Vac. Sci. Technol. B 23, 3164 (2005); http://dx.doi.org/10.1116/1.2127948 (4 pages) | Cited 11 times

Online Publication Date: 7 December 2005

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We developed an integrated circular polarizer based on stacking an aluminum nano-wire grid polarizer with a dielectric nano-grating-based quarter waveplate. The polarizer consists of 65 nm wide and 130 nm tall aluminum wires with a period of 148 nm. For integration, the aluminum nanowires were buried into a silicon dioxide matrix by a trench filling and planarization technology. The buried nanowire polarizer achieved excellent optical performance in a broad wavelength range from 400 nm to >900 nm. On top of the buried and planarized nanowire polarizer, a visible quarter waveplate based on a 200 nm period silicon nitride nano-grating was fabricated. Both the 148 nm period aluminum grating and the 200 nm period silicon nitride grating were fabricated by an ultraviolet (UV)-nanoimprint lithography. The ability to integrate multiple nanostructure-based optical layers opens a path for novel integrated optical devices, as well as a new strategy for driving both miniaturization and cost.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Gw Other integrated-optical elements and systems
42.79.Dj Gratings
81.16.Nd Micro- and nanolithography

Lithographically fabricated optical cavities for refractive index sensing

Mark Adams, Guy A. DeRose, Marko Loncar, and Axel Scherer

J. Vac. Sci. Technol. B 23, 3168 (2005); http://dx.doi.org/10.1116/1.2127945 (6 pages) | Cited 7 times

Online Publication Date: 7 December 2005

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Since the development of distributed Bragg gratings, high resolution lithography and etching have been applied towards the concentration of light. The most important application of lithographically fabricated microcavities has been for the spectral control over laser emission. Here we describe the opportunities that arise from further miniaturization of laser cavities by using high index contrast photonic crystal mirrors and annular Bragg reflectors. We have used these optical cavities, with mode volumes as small as 10−17 l, to perform spectroscopic analysis and compare the mode volumes and sensitivities of these geometries.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Tv Photonic crystal lasers and coherent effects
42.55.Sa Microcavity and microdisk lasers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.60.By Design of specific laser systems
42.79.Dj Gratings
42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
back to top Carbon Nanotube Technology

Electrodes for carbon nanotube devices by focused electron beam induced deposition of gold

T. Brintlinger, M. S. Fuhrer, J. Melngailis, I. Utke, T. Bret, A. Perentes, P. Hoffmann, M. Abourida, and P. Doppelt

J. Vac. Sci. Technol. B 23, 3174 (2005); http://dx.doi.org/10.1116/1.2130355 (4 pages) | Cited 28 times

Online Publication Date: 7 December 2005

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Individual carbon nanotubes (CNTs) often occur in randomly dispersed two-dimensional as well as three-dimensional configurations that make device fabrication difficult. Making electrical contact to such CNTs is of practical interest. To this end, we make contact to individual metallic single-walled carbon nanotubes (SWNTs) using the focused electron-beam-induced deposition (FEBID) of pure gold. The SWNTs are grown by chemical vapor deposition on a flat substrate, and the gold leads are made through FEBID using inorganic metallic precursor gas, chloro(trifluorophosphine)gold(I), or AuClPF3, in a high vacuum scanning electron microscope. The same scanning electron microscope is also used to image carbon nanotubes, allowing for simultaneous alignment. We find equivalent one-dimensional resistivities for the SWNTs of 10–15 kΩ/μm for both FEBID gold leads and leads deposited using conventional electron-beam lithography (EBL) and thermal evaporation of gold, suggesting similarly low contact resistances. We use electrostatic force microscopy to verify quantitatively similar contact resistances for one nanotube sample, 10 (±6) and 54 (±6) kΩ, for FEBID and EBL leads, respectively, with most voltage dropping across the long metallic SWNT.
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73.40.Jn Metal-to-metal contacts
73.40.Cg Contact resistance, contact potential
82.45.Yz Nanostructured materials in electrochemistry
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
85.35.Kt Nanotube devices

Positioning of carbon nanotubes using soft-lithography for electronics applications

N. O. V. Plank, Masahiko Ishida, and R. Cheung

J. Vac. Sci. Technol. B 23, 3178 (2005); http://dx.doi.org/10.1116/1.2134713 (4 pages) | Cited 1 time

Online Publication Date: 7 December 2005

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Carbon nanotubes (CNTs) devices have been fabricated using two similar microfabrication processes involving poly(dimethylsiloxane) (PDMS) molecular stamping of 2-thiolpyridine and subsequent self-assembly of CNTs. The two methods allow the fabrication of CNT devices with >90% yield. From Vg = −5 to +5 V, when Ti–Au electrodes are fabricated on top of the self-assembled CNT films, our devices exhibit p-type field-dependent behavior. When the CNTs have been self-assembled across pre-defined Ti–Au electrodes, metallic conduction has been observed. The electronic properties of our back-gated CNT devices are found to depend upon CNT concentration in the original self-assembly solution. The final structure of the CNT device can affect the field dependency as a result of screening effects at the contact regions, with the 2-thiolpyridine acting as a further screening region.
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85.35.Kt Nanotube devices
81.16.Nd Micro- and nanolithography
81.16.Dn Self-assembly
back to top Advanced Lithography Applications

Direct measurements and analyses of the Coulomb effects in electron projection lithography

Jiro Yamamoto, Hiroshi Yamashita, Hiroshi Arimoto, Junji Ikeda, Shohei Suzuki, and Shintaro Kawata

J. Vac. Sci. Technol. B 23, 3182 (2005); http://dx.doi.org/10.1116/1.2131085 (6 pages) | Cited 1 time

Online Publication Date: 7 December 2005

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The Coulomb effects have been common problems in electron-beam lithography. In our previous article, we studied the influence of the Coulomb effects on electron projection lithography (EPL) process. In this paper, we analyze the Coulomb effects by direct blur measurements and by simulations. We found that there existed a beam blur around 32 nm at a low beam current (approximately 0 μA). We found a relationship between the beam blur and the beam current that was 5.4 nm/μA, and this number agreed with our simulation work as well as with our experiment with resist resolution. We learned that at low current the blur was so small that a blur distribution could be practically ignored. An important finding we had, is that the beam blur did not only depend on the beam current but also on the pattern arrangement. We found the possibility of the existence of the local Coulomb effects and estimated its range to be around 100–120 μm on our system. These phenomena should be taken into considerations when making proximity effect correction for highly accurate critical dimension control.
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85.40.Hp Lithography, masks and pattern transfer

Proximity effect correction using blur map in electron projection lithography

Hiroshi Yamashita, Jiro Yamamoto, Fumihiro Koba, and Hiroshi Arimoto

J. Vac. Sci. Technol. B 23, 3188 (2005); http://dx.doi.org/10.1116/1.2101791 (5 pages)

Online Publication Date: 7 December 2005

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We demonstrate and evaluate proximity effect correction using blur map at a compromised focal plane in electron projection lithography. Critical dimension (CD) accuracy was improved from 12 to 5 nm for 100 nm L/S pattern with 34% pattern area density by using blur maps calculated by space charge effect correction (SCEC) program, which is provided with the electron beam stepper NSR-EB1A by Nikon. CD error due to the SCEC was estimated to be 4 nm, corresponding to 6 nm in terms of blur for the resist process; this is substantiated by comparing the calculated and measured blurs that ranged from 6.3 to −4.3 nm.
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85.40.Hp Lithography, masks and pattern transfer

Integrated four-channel GaAs-based quantum dot laser module with photonic crystals

H. Scherer, K. Namje, S. Deubert, A. Löffler, J. P. Reithmaier, M. Kamp, and A. Forchel

J. Vac. Sci. Technol. B 23, 3193 (2005); http://dx.doi.org/10.1116/1.2062347 (4 pages)

Online Publication Date: 7 December 2005

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The integration of a four channel laser array with photonic crystals is demonstrated. The devices have been fabricated on GaAs quantum dot layers with an emission wavelength of 1.3 μm. A double stage photonic crystal combiner is used to combine the emission of four tunable ridge-waveguide lasers with photonic crystal mirrors into a single output waveguide. The lasers can be operated separately or simultaneously, resulting in four separately selectable wavelengths in the output signal. Threshold currents of single lasers are around 30 mA and sidemode suppression ratios up to 30 dB have been achieved. Continuous operation of all four lasers is observed up to temperatures of 40 °C.
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42.60.By Design of specific laser systems
42.82.Bq Design and performance testing of integrated-optical systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Fabrication of a hard mask for InP based photonic crystals: Increasing the plasma-etch selectivity of poly(methyl methacrylate) versus SiO2 and SiNx

R. Wüest, P. Strasser, F. Robin, D. Erni, and H. Jäckel

J. Vac. Sci. Technol. B 23, 3197 (2005); http://dx.doi.org/10.1116/1.2062567 (5 pages) | Cited 11 times

Online Publication Date: 7 December 2005

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We introduce cyclic reactive ion etching processes for SiO2 and SiNx hard masks where the fluorine-based etch steps are interleaved with N2 flushing steps in order to improve the selectivity to electron-beam resists. For SiO2 etching an etch-step duration of 30 s resulted in a doubled selectivity of almost 4:1 between SiO2 and poly(methyl methacrylate) (PMMA) due to a reduced thermal load. We established the pattern transfer from a 200 nm thick PMMA resist into a 600 nm thick SiO2 layer for 200 nm diameter holes. For SiNx etching we demonstrate improved sidewall verticality, an enhanced etch rate, and suppressed redeposition of etch byproducts for a cyclic process. With the use of an additional 30 nm titanium intermediate layer we show an excellent overall selectivity between SiNx and PMMA of almost 5:1. This process is applied to the fabrication of planar photonic-crystal devices with 3.5 μm deep holes in an InP based slab waveguide with an initial PMMA layer thickness of 220 nm.
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42.70.Qs Photonic bandgap materials
81.05.Ea III-V semiconductors
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
back to top Micro- and Nano-machining Techniques

Subcritical carbon dioxide assisted polymer nanofabrication at low temperatures

Yong Yang, Ly James Lee, and Wu Lu

J. Vac. Sci. Technol. B 23, 3202 (2005); http://dx.doi.org/10.1116/1.2134714 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2005

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Polymer-based micro/nanoelectromechanical systems have attracted a great deal of interest from industries and academia. The common polymer fabrication methods involve either organic solvents or temperatures above the glass transition temperature, which is undesirable, particularly at the nanoscale. On the basis of different properties near polymer surfaces from those in the bulk, we introduce subcritical fluids [particularly carbon dioxide (CO2)] into polymer surfaces to manipulate the polymer properties at the nanoscale so that we can achieve low temperature polymer nanofabrication. Guided by CO2-enhanced surface dynamics of polymers, we developed a CO2 bonding technique to succeed in low temperature assembly of polymeric nanostructures. This CO2 bonding technique has been applied to seal polymeric nanofluidic biochips and construct well-defined three-dimensional biodegradable polymeric scaffolds for tissue engineering.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
68.35.Ja Surface and interface dynamics and vibrations

Formation of GaN layer on SiN surface using low-energy Ga ion implantation

Junichi Yanagisawa, Masaya Toda, Takeshi Kitamura, Hiroyoshi Matsumoto, and Yoichi Akasaka

J. Vac. Sci. Technol. B 23, 3205 (2005); http://dx.doi.org/10.1116/1.2134722 (4 pages) | Cited 2 times

Online Publication Date: 7 December 2005

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As a new method for fabricating gallium nitride (GaN) layers at the outer surface of silicon nitride (SiN) films, low-energy Ga ion irradiation on SiN films was performed, and the composition of the surface and the chemical-bond nature of the irradiated surfaces were measured by x-ray photoelectron spectroscopy (XPS). The peak position of the XPS spectrum of Ga 3d from the Ga irradiated SiN was shifted from the value of the metallic Ga to that of GaN, indicating the formation of GaN on the Ga irradiated SiN surface. Formation of GaN was also confirmed from the XPS spectra of N 1s signals. It was also found that a Ga irradiation energy up to 4 keV was useful to form GaN, and the implanted Ga atoms remained on the SiN surface as GaN after an annealing at 500 °C for 5 min under N2 gas pressure of 1×10−4 Torr. Because GaN which was formed is positioned at the outermost region of the Ga irradiated SiN films, the possibility to use this surface as a substrate for the GaN growth is discussed.
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81.05.Ea III-V semiconductors
61.72.up Other materials
68.35.Dv Composition, segregation; defects and impurities
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.72.Cc Kinetics of defect formation and annealing

Filling high aspect-ratio nano-structures by atomic layer deposition and its applications in nano-optic devices and integrations

Jian Jim Wang, Xuegong Deng, Ron Varghese, Anguel Nikolov, Paul Sciortino, Feng Liu, Lei Chen, and Xiaoming Liu

J. Vac. Sci. Technol. B 23, 3209 (2005); http://dx.doi.org/10.1116/1.2132326 (5 pages) | Cited 7 times

Online Publication Date: 7 December 2005

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Atomic layer deposition, a highly uniform and conformal deposition process, was utilized to fill trenches of various high aspect-ratio nano-grating structures. Dielectric (e.g., SiO2), metal (e.g., aluminum), and dielectric/metal (e.g., Au/SiO2) hybrid nano-gratings with a linewidth down to <50 nm and an aspect ratio up to 14:1 (700 nm:50 nm) were trench-filled with various materials particularly nano-laminate materials such as TiO2/SiO2 and SiO2/Al2O3. Various high-performance optical devices such as true-zero-order optical retarders (i.e., wave plates) and nanowire-grid polarizers were realized based on an UV-nanoimprint lithography process and the atomic layer deposition for trench fillings. Thanks to both unique material properties and nano-structure trench filling capability, the atomic layer deposition opens a path for innovative nano-structure based optical devices and integrated optical devices.
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42.79.Dj Gratings
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Bc Nanocrystalline materials
42.82.-m Integrated optics
42.79.Ci Filters, zone plates, and polarizers

Fabrication of a Si/SiO2 multiple-quantum-well light emitting diode using remote plasma enhanced chemical vapor deposition

R. Rölver, S. Brüninghoff, M. Först, B. Spangenberg, and H. Kurz

J. Vac. Sci. Technol. B 23, 3214 (2005); http://dx.doi.org/10.1116/1.2074867 (5 pages) | Cited 4 times

Online Publication Date: 7 December 2005

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Photoluminescence (PL) and electroluminescence (EL) measurements are performed on Si/SiO2 multiple quantum wells fabricated by using a combination of remote plasma enhanced chemical vapor deposition (RPECVD) and rapid thermal annealing (RTA). A significant enhancement of light emission is observed from nanocrystalline Si wells embedded in a SiO2 matrix. The enhancement depends critically on additional annealing processes carried out after the RPECVD deposition.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
78.67.De Quantum wells
81.07.St Quantum wells
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Ap Elemental semiconductors
78.60.Fi Electroluminescence
61.72.Cc Kinetics of defect formation and annealing
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