Browse - Journal of Vacuum Science & Technology B

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High temperature imaging using a thermally compensated cantilever resistive probe for scanning thermal microscopy

Y. Zhang, P. S. Dobson, and J. M. R. Weaver

J. Vac. Sci. Technol. B 30, 010601 (2012); http://dx.doi.org/10.1116/1.3664328 (5 pages)

Online Publication Date: 1 December 2011

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The authors have designed and fabricated AFM probes with an integrated resistive temperature sensor and a grooved cantilever structure. The grooved structure compensates for the bilayer thermal bending that normally occurs during scanning thermal microscopy of hot samples. These new probes show reduced bending at high temperatures when compared to commercial, conventional cantilever probes with a similar stiffness. This indicates that the mechanical balance introduced by the grooved structure plays a major role in reducing thermal bending. Successful temperature mapping is demonstrated on an active heater device reaching 108 °C, a sample that would be beyond the imaging capability of conventional probes.

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07.07.Df

Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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Effect of annealing on interfacial and band alignment characteristics of HfO₂/SiO₂ gate stacks on Ge substrates

Xue-Fei Li, Xiao-Jie Liu, Ying-Ying Fu, Ai-Dong Li, Wen-Qi Zhang, Hui Li, and Di Wu

J. Vac. Sci. Technol. B 30, 010602 (2012); http://dx.doi.org/10.1116/1.3665416 (4 pages)

Online Publication Date: 5 December 2011

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The authors have investigated the effect of 500 °C annealing for 60 s in N₂ on interfacial and band alignment characteristics of HfO₂/SiO₂ gate stacks on n-type Ge substrates. X-ray photoelectron spectroscopy analyses reveal that the SiO₂ interlayer can effectively suppress Ge outdiffusion during HfO₂ growth and subsequent postdeposition annealing process. The electrical measurement shows that capacitance equivalent thickness of 1.75 nm and a leakage current density of 3.9 × 10⁻³ A/cm² at gate bias of flatband voltage (V_fb) + 1 V was obtained for the annealed sample. The conduction band offsets at the HfO₂/SiO₂/Ge with and without annealing are found to be 2.22 and 2.07 eV, respectively.

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79.60.Jv	Interfaces; heterostructures; nanostructures
73.20.At	Surface states, band structure, electron density of states
81.40.Gh	Other heat and thermomechanical treatments

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Extraction of a low-current discharge from a microplasma for nanoscale patterning applications at atmospheric pressure

Seung Whan Lee, Hamidreza Zamani, Philip X.-L. Feng, and R. Mohan Sankaran

J. Vac. Sci. Technol. B 30, 010603 (2012); http://dx.doi.org/10.1116/1.3669523 (5 pages)

Online Publication Date: 15 December 2011

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The authors present a scheme to extract a low-current discharge from a microplasma at atmospheric pressure for nanopatterning applications. The extracted discharge is generated by applying a high positive voltage to an independent electrode and accelerating electrons from the microplasma. Current-voltage (I–V) characteristics of the extracted discharge show high stability at low currents and tunability over a wide range of currents. Exposure of metal precursor loaded films to the extracted discharge results in electrochemical reduction of metal ions to solid metal, as confirmed by X-ray photoelectron spectroscopy. Combining this approach with masking techniques allows the transfer of nanoscale patterns of metal at ambient conditions.

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81.16.Rf	Micro- and nanoscale pattern formation
73.61.At	Metal and metallic alloys
79.60.Bm	Clean metal, semiconductor, and insulator surfaces

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Determination of crystal orientation of silicon via shape-controlled vapor-solid growth of copper nanoparticles

Jin-Woo Han and M. Meyyappan

J. Vac. Sci. Technol. B 30, 010604 (2012); http://dx.doi.org/10.1116/1.3672007 (4 pages)

Online Publication Date: 21 December 2011

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Crystal lattice orientations of substrates are inspected via morphology of copper particles generated by a vapor-solid growth process. The high thermal energy enables diffusion of copper ions into the crystal substrate, and then the copper ions on the substrate are preferentially gathered, forming single-crystalline metal particles. The shapes of the particles are bounded by the facets to minimize the surface energy. Thus, polyhedral particles are truncated and bounded by {100}, {110}, and {111} facets, which results in equilateral square and triangle shapes on (100) and (111) plane substrates, respectively. The directions of the sides of the square and triangle shapes indicate <100> and <110> directions, respectively.

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61.50.-f	Structure of bulk crystals
68.35.Md	Surface thermodynamics, surface energies
81.07.Bc	Nanocrystalline materials
81.10.Bk	Growth from vapor
81.10.Dn	Growth from solutions
66.30.J-	Diffusion of impurities

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Directed assembly in epitaxial zinc oxide films on focused ion beam modified sapphire substrates

Benjamin D. Myers, Blake L. Stevens, Dorota I. Rożkiewicz, Scott A. Barnett, and Vinayak P. Dravid

J. Vac. Sci. Technol. B 30, 010605 (2012); http://dx.doi.org/10.1116/1.3672006 (5 pages)

Online Publication Date: 22 December 2011

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A new method for directed self-assembly using focused ion beam (FIB) and physical vapor deposition is presented. The high resolution and site-specific patterning capabilities of FIB are coupled with the self-assembly process in heteroepitaxial thin film growth. An efficient FIB-induced damage mechanism is exploited to pattern amorphous regions in sapphire substrates which direct the subsequent assembly of a sputter-deposited zinc oxide film. This novel approach allows for the fabrication of in-plane nano- to microscale heterostructures comprising epitaxial regions with high strain and defect density that are separated by regions of randomly oriented (in-plane) grains with much lower strain and defect density.

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81.15.Kk	Vapor phase epitaxy; growth from vapor phase
68.55.ag	Semiconductors
61.72.-y	Defects and impurities in crystals; microstructure
81.05.Dz	II-VI semiconductors

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Carbon monoxide detection sensitivity of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors in different temperature environments

Chien-Fong Lo, Lu Liu, Byung-Hwan Chu, Fan Ren, Stephen J. Pearton, Sylvain Doré, Chien-Hsing Hsu, Jihyun Kim, Amir M. Dabiran, and Peter P. Chow

J. Vac. Sci. Technol. B 30, 010606 (2012); http://dx.doi.org/10.1116/1.3672010 (4 pages)

Online Publication Date: 22 December 2011

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The effect of ambient temperature on the detection sensitivity of carbon monoxide (CO) using ZnO nanorod-gated AlGaN/GaN high electron mobility transistor (HEMT) sensors was studied over a range of temperatures from 25 to 400 °C. An increase of the HEMT drain current was observed for exposure to the CO-containing ambients, due to chemisorbed oxygen on the ZnO surface reacting with CO to form CO₂ and releasing electrons to the oxide surface, increasing the counter charges in the two-dimensional electron gas channel of the HEMT. By increasing the detection temperature from 25 °C to 150 °C, the CO detection sensitivity, ΔI/I, and detection limit were significantly improved from 0.23% to 7.5% and from 100 ppm to ∼30 ppm, respectively. However, the sensitivity of the CO detection was degraded by the decrease of mobility and saturation drain current of HEMT at temperatures higher than 200 °C.

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85.30.Tv	Field effect devices
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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Fabrication of stable and reproducible submicron tunnel junctions

I. M. Pop, T. Fournier, T. Crozes, F. Lecocq, I. Matei, B. Pannetier, O. Buisson, and W. Guichard

J. Vac. Sci. Technol. B 30, 010607 (2012); http://dx.doi.org/10.1116/1.3673790 (4 pages)

Online Publication Date: 6 January 2012

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The authors have performed a detailed study of the time stability and reproducibility of submicron Al/AlO_x/Al tunnel junctions, fabricated using standard double angle shadow evaporations. The authors have found that by aggressively cleaning the substrate before the evaporations; thus preventing any contamination of the junction, they obtained perfectly stable oxide barriers. The authors also present measurements on large ensembles of junctions which prove the reproducibility of the fabrication process. The measured tunnel resistance variance in large ensembles of identically fabricated junctions is in the range of only a few percent. Finally, the authors have studied the effect of different thermal treatments on the junction barrier. This is especially important for multiple step fabrication processes which imply annealing the junction.

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73.40.Gk	Tunneling
73.40.Ns	Metal-nonmetal contacts
81.65.Cf	Surface cleaning, etching, patterning

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Recent developments and design challenges in continuous roller micro- and nanoimprinting

Jarrett J. Dumond and Hong Yee Low

J. Vac. Sci. Technol. B 30, 010801 (2012); http://dx.doi.org/10.1116/1.3661355 (28 pages)

Online Publication Date: 1 December 2011

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As an emerging technology for the manufacture of micro- and nano-scale patterns, continuous imprinting; otherwise known as roll-to-roll or roller imprinting, is attracting interest from researchers around the world because of its inherent advantages of low cost, high throughput, large area patterning. This technology is an evolutionary advance on the more traditional nanoimprint lithography developed in the 1990s, which is considered a batch mode, or dis-continuous patterning approach. In recent years, a number of commercial applications have been discovered which require low cost, large area patterning, particularly displays, optical coatings and films, and biological applications such as anti-fouling surfaces and micro-fluidic devices. This review covers a variety of continuous imprinting approaches, highlights challenges, and surveys progress towards high speed production of micro- and nanoscale features for these applications and others using this platform technology.

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81.16.Nd	Micro- and nanolithography
81.16.Rf	Micro- and nanoscale pattern formation

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Two-bit/four-level Pr₂O₃ trapping layer for silicon-oxide-nitride-oxide-silicon-type flash memory

Yu-Hsien Lin, Hsin-Chiang You, and Chao-Hsin Chien

J. Vac. Sci. Technol. B 30, 011201 (2012); http://dx.doi.org/10.1116/1.3668101 (4 pages)

Online Publication Date: 9 December 2011

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This study proposes and demonstrates a silicon-oxide-nitride-oxide-silicon (SONOS)-type memory device based on a high-k dielectric praseodymium oxide (Pr₂O₃) trapping layer. In the proposed design, channel hot electron injection programming and band-to-band hot-hole injection erasing allow highly efficient two-bit and four-level device operation. The proposed design also has a total memory window of 5 V, a ten-year V_t retention window larger than 0.8 V between adjacent levels, and enough memory window for 10⁵ programming/erasing cycles of endurance. The proposed SONOS-type Pr₂O₃ trapping layer flash memory exhibits large memory windows, high program/erase speed, good endurance, and good disturbance characteristics.

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84.30.Sk

Pulse and digital circuits

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Physical and electrical properties of thermally oxidized dielectrics on Si-capped Ge-on-Si substrate

Yuanyu Zheng, Guanzhou Liu, Cheng Li, Wei Huang, Songyan Chen, and Hongkai Lai

J. Vac. Sci. Technol. B 30, 011202 (2012); http://dx.doi.org/10.1116/1.3668115 (4 pages)

Online Publication Date: 9 December 2011

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Thermal oxidation of silicon (Si)-capped germanium (Ge) epilayer on Si substrate is performed to study the effect of the physical interface on the electrical properties of Ge metal-oxide-semiconductor capacitors. During the growth and oxidation of the Si cap layer, Ge atoms diffuse through the Si cap layer, and they are oxidized to GeO₂. Once the Si cap layer is consumed, more Ge suboxides are generated, resulting in the serious degradation of the capacitance-voltage characteristics. Both the positive fixed charges generated by the evaporation of GeO and the negative fixed charges induced by the formation of Si-O- dangling bonds are proposed to affect the flat-band voltage shifts. These results suggest that the deposition of a thin Si cap layer on Ge is effective in suppressing the generation of Ge sub-oxides during thermal oxidation, thereby improving the performance of Ge capacitors.

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85.30.Tv	Field effect devices
84.32.Tt	Capacitors

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Simulation and experimental study of ArF 193 nm laser lift-off AlGaN/GaN high electron mobility transistors

T. S. Kang, X. T. Wang, C. F. Lo, F. Ren, S. J. Pearton, O. Laboutin, Yu Cao, J. W. Johnson, and Jihyun Kim

J. Vac. Sci. Technol. B 30, 011203 (2012); http://dx.doi.org/10.1116/1.3664283 (5 pages)

Online Publication Date: 21 December 2011

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A finite element simulation was used to estimate the temperature distributions within AlGaN/GaN high electron mobility transistors (HEMTs) during the laser lift-off process. The time-dependent simulation showed that a thin layer of GaN at the GaN/sapphire interface was heated up to around 1600 K in less than 25 ns by a pulsed laser exposure with a duration of 25 ns and a fluence of 800 mJ/cm² to decompose this GaN layer into Ga and nitrogen. Experimentally, there was a threshold fluence around 550 mJ/cm², corresponding to 1300 K at the GaN/sapphire interface, for partially lifting off the HEMT structure from the sapphire. The simulated temperature at the GaN/sapphire interface with a fluence of 420 mJ/cm² never reached above 1000 K, however, the HEMT structure was lifted-off by multiple laser exposures at this fluence. Therefore, instead of thermally induced decomposition, the lift-off mechanism could also be through the Ga–N bond breaking during the multiple lower-fluence high-energy 193 nm laser exposures.

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85.30.Tv

Field effect devices

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Electron field emission from undoped polycrystalline diamond particles synthesized by microwave-plasma chemical vapor deposition

Kenji Nose, Ryuhei Fujita, Masao Kamiko, and Yoshitaka Mitsuda

J. Vac. Sci. Technol. B 30, 011204 (2012); http://dx.doi.org/10.1116/1.3670988 (6 pages)

Online Publication Date: 21 December 2011

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Electron emission from polycrystalline diamond particles (PDPs) was obtained at low electric fields in the absence of intentional doping. The PDPs were synthesized on a silicon substrate using microwave-plasma chemical vapor deposition accompanied by bias-enhanced nucleation. Polycrystalline diamond particles of two different sizes, i.e., ∼500 nm and 2 to 5 μm, were obtained, the surfaces of which were covered with small crystal grains composed of fine facets. Electron emission from the PDPs was characterized by Fowler-Nordheim tunneling with low turn-on-field values (0.8 – 2.0 V/μm) and a low barrier height of 0.02 eV. An emission current greater than 5 μA was maintained for over 24 h in a cathode based on the developed PDPs. In contrast, single-crystalline diamond particles prepared for comparative purposes exhibited no emission up to 2.5 V/μm. Auger electron spectroscopy revealed that the surface oxygen content modified by annealing in air did not affect the emission properties. The macroscopic spatial distribution of the emission spots was roughly consistent with the population density distribution of PDPs on the cathode. It is postulated that emission from the PDPs arises as a result of the small crystal grains on the surface and the presence of a sp²-bonded phase in the grain boundaries, which enabled strong field enhancement and carrier transport through the undoped diamond particles.

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81.05.ug	Diamond
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy	Elemental semiconductors
79.70.+q	Field emission, ionization, evaporation, and desorption
79.20.Fv	Electron impact: Auger emission
73.40.Gk	Tunneling

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Effect of buffer layer structure on electrical and structural properties of AlGaN/GaN high electron mobility transistors

Chien-Fong Lo, L. Liu, T. S. Kang, Fan Ren, O. Laboutin, Y. Cao, J. W. Johnson, Alexander Y. Polyakov, N. B. Smirnov, A. V. Govorkov, I. A. Belogorokhov, A. I. Belogorokhov, and S. J. Pearton

J. Vac. Sci. Technol. B 30, 011205 (2012); http://dx.doi.org/10.1116/1.3671020 (7 pages)

Online Publication Date: 21 December 2011

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AlGaN/GaN high electron mobility transistors (HEMTs) with similar active layers structures were grown on SiC or sapphire substrates using different buffer layer structures, including GaN of different thickness (1 or 2 μm) or composite AlGaN/GaN buffers. The highest density of hole traps was observed in the buffer on sapphire, while the lowest density of hole traps was obtained in the thick (2 μm) GaN buffer on SiC. The reverse leakage currents in HEMTs were lower in the devices grown on SiC substrates and the on-off ratios improved by two orders of magnitude for thicker GaN buffers or composite AlGaN/GaN buffers compared to a standard 1 μm GaN buffer. The maximum drain-source currents and tranconductances were all larger for the devices on SiC compared to sapphire.

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85.30.Tv

Field effect devices

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Role of ions, photons, and radicals in inducing plasma damage to ultra low-k dielectrics

Hualiang Shi, Huai Huang, Junjing Bao, Junjun Liu, Paul S. Ho, Yifeng Zhou, Jeremy T. Pender, Michael D. Armacost, and David Kyser

J. Vac. Sci. Technol. B 30, 011206 (2012); http://dx.doi.org/10.1116/1.3671008 (9 pages)

Online Publication Date: 22 December 2011

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The damage induced by CO₂ and O₂ plasmas to an ultra low-k (ULK) dielectric film with a dielectric constant (κ) of 2.2 was investigated. The dielectric constant was observed to increase due to methyl depletion, moisture uptake, and surface densification. A gap structure was used to delineate the role of ions, photons and radicals in inducing the damage, where the experimental variables included an optical mask (MgF₂, fused silica, and Si), a gap height, an inductively coupled plasma power source, a bias power on the bottom electrode, variable chamber pressure, and variable substrate temperature. The plasma radical density distribution inside the gap between the optical mask and the ULK film was simulated. The simulation was based on radical diffusion, reaction, and recombination inside the gap. The experimental results and the numerical simulation showed that the oxygen radicals played an important role in plasma induced damage which was found to be proportional to the oxygen radical density and enhanced byvacuum ultraviolet (VUV) photon radiation. Under certain experimental conditions, ion bombardment can induce surface densification and suppress radical diffusion. The role of UV and VUV photons in induced damage was investigated with Ar plasma using the gap structure and it was found that the photons can induce surface damage directly.

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77.22.Ch	Permittivity (dielectric function)
77.55.Bh	Low-permittivity dielectric films
81.20.Ev	Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
52.40.Hf	Plasma-material interactions; boundary layer effects
61.80.Jh	Ion radiation effects

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Strategy for focused ion beam compound material removal for circuit editing

Yariv Drezner, Yuval Greenzweig, and Amir Raveh

J. Vac. Sci. Technol. B 30, 011207 (2012); http://dx.doi.org/10.1116/1.3674280 (9 pages) | Cited 1 time

Online Publication Date: 6 January 2012

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Both selective and nonselective focused ion beam (FIB) processes have become critical for enabling fine-scale activities such as nano-machining and nano-fabrication in compound material removal applications. In this paper, we investigate the influence of FIB ion acceleration voltage on gas assisted etch rates for the most frequently used materials in the microelectronic industry, using common FIB etchants. These results can serve as a baseline for FIB process development using various materials for both highly-selective and (almost) nonselective material removal. Etching strategies are suggested. Two test cases are presented here, in which we performed either selective or nonselective material removal processes. The etch rate of different materials was found to be dependent on acceleration voltage, and very specific to the material-precursor system.

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81.65.Cf	Surface cleaning, etching, patterning
52.77.Bn	Etching and cleaning
81.16.-c	Methods of micro- and nanofabrication and processing
06.60.Vz	Workshop procedures (welding, machining, lubrication, bearings, etc.)
81.20.Wk	Machining, milling

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Deep anisotropic LiNbO₃ etching with SF₆/Ar inductively coupled plasmas

Deng Jun, Jia Wei, Ching Eng Png, Si Guangyuan, Jaesung Son, Hyunsoo Yang, and Aaron J. Danner

J. Vac. Sci. Technol. B 30, 011208 (2012); http://dx.doi.org/10.1116/1.3674282 (6 pages)

Online Publication Date: 6 January 2012

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A SF₆/Ar inductively coupled plasma (ICP) technique was investigated to improve etching of proton exchanged LiNbO₃. The influences of He backside cooling, power, and gas flows on characteristics such as etching rate, sidewall slope angle, and surface roughness were investigated. Total gas flow is a key parameter that affects etching results, and an optimized gas flow (50 sccm) was used for lengthy etching processes (30 min). Deep (>3 μm) and highly anisotropic etching, as well as ultra smooth LiNbO₃ surfaces were achieved in a single-step run. The authors’ proposed method has achieved the deepest, most vertical, minimal residue structure yet reported for single-step ICP etching.

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81.65.Cf	Surface cleaning, etching, patterning
82.30.Hk	Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
52.77.Bn	Etching and cleaning

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Integration of a thin film III–V edge emitting laser and a polymer microring resonator on an SiO₂/Si substrate

Sabarni Palit, Matthew Royal, Nan Jokerst, Jeremy Kirch, and Luke Mawst

J. Vac. Sci. Technol. B 30, 011209 (2012); http://dx.doi.org/10.1116/1.3676031 (5 pages)

Online Publication Date: 12 January 2012

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The planar integration of on-chip laser sources with optical sensing elements, waveguide optical interconnect, and detectors enables the implementation of portable, efficient chip-scale systems, with applications in areas that include medical, environmental, biological, and chemical sensing systems. In this paper, the planar integration of a thin film strain compensated In_0.2Ga_0.8As/GaAs single quantum well laser with a tapered polymer (SU-8-2002) waveguide and overlap coupled SU-8-2002 microring resonator is achieved on an SiO₂/Si platform. Two laser/waveguide configurations, one with the tapered waveguide separated from the laser front facet and the other with the waveguide overlapping the front facet, were demonstrated, and this laser/waveguide structure was then integrated with a polymer microring resonator on SiO₂/Si. Lasing operation for the integrated system was verified through power-current characteristics and spectra at the through and drop ports of the microring resonator. This integrated system forms an essential component toward realizing planar chip-scale optical sensing systems.

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42.55.Px	Semiconductor lasers; laser diodes
42.60.By	Design of specific laser systems
42.79.Gn	Optical waveguides and couplers
42.82.Ds	Interconnects, including holographic interconnects
42.82.Et	Waveguides, couplers, and arrays

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Adhesion and frictional force measurements employing scanning probe microscopy in a pentafluoropropane gas atmosphere

Makoto Okada, Masayuki Iwasa, Hiroshi Hiroshima, Yuichi Haruyama, Kazuhiro Kanda, and Shinji Matsui

J. Vac. Sci. Technol. B 30, 011601 (2012); http://dx.doi.org/10.1116/1.3665989 (3 pages)

Online Publication Date: 9 December 2011

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Ultraviolet (UV) nanoimprinting is a useful technique to fabricate nanostructure devices with high throughput, high resolution, and low cost. To eliminate bubble defects, one of the main problems in UV nanoimprinting, UV nanoimprinting in an atmosphere of pentafluoropropane (PFP) gas, which is a condensable gas, is proposed. This process has been reported to reduce the demolding force. To examine the PFP gas effect in a nanometer-scale area, adhesion and frictional forces were measured by scanning probe microscopy in a PFP gas atmosphere. The results show that the adhesion and frictional forces measured by scanning probe microscopy in a PFP gas atmosphere were lower than those measured in air and a N₂ gas atmosphere. Furthermore, the adhesion and frictional forces were found to depend on the PFP gas pressure.

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81.16.Nd	Micro- and nanolithography
81.40.Pq	Friction, lubrication, and wear
62.20.Qp	Friction, tribology, and hardness
68.35.Np	Adhesion

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Viscoelastic properties measurements of thin polymer films from reflow of nanoimprinted patterns

Etienne Rognin, Stefan Landis, and Laurent Davoust

J. Vac. Sci. Technol. B 30, 011602 (2012); http://dx.doi.org/10.1116/1.3664088 (4 pages)

Online Publication Date: 15 December 2011

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The authors describe in this paper a fast and cost-effective method to measure the viscoelastic properties of a thin polymer film from the reflow of nanoimprinted patterns. The material is spin-coated onto a silicon substrate and specially designed nanopatterns are imprinted on the film using thermal nanoimprint. A first measurement of the imprinted profile is done by atomic force microscopy (AFM). The film is then heated at a definite temperature above the glass transition temperature during a definite time. The film is rapidly cooled down and the reflowed profile is again measured by AFM. Spectral densities of the profiles are computed using standard Fourier transform algorithms, and the viscoelastic properties are computed as fitting parameters of an evolution model for the spectral density of the topology. The originality of our method is based on the accurate spatial description of the imprint rather than on its temporal decay. Using our approach, we measured the viscoelastic properties of a 205 nm-thick polystyrene (molecular weight 130 kg/mol) film, assuming a single relaxation time Maxwell model.

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81.05.Lg	Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
62.40.+i	Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs	Mechanical and acoustical properties
81.16.Rf	Micro- and nanoscale pattern formation
81.16.Nd	Micro- and nanolithography
81.40.Jj	Elasticity and anelasticity, stress-strain relations

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Self-aligned patterning on a flexible substrate using a dual-tone, thermally activated photoresist

Wei-Lun K. Jen, Brandon M. Rawlings, Jeffrey R. Strahan, Daniel J. Hellebusch, William J. Durand, and C. Grant Willson

J. Vac. Sci. Technol. B 30, 011603 (2012); http://dx.doi.org/10.1116/1.3669380 (7 pages)

Online Publication Date: 10 January 2012

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The fabrication of electronic devices on flexible substrates represents an opportunity for the development of flexible display technologies, large area devices, and roll-to-roll manufacturing processes. Traditional photolithography encounters alignment and overlay limitations when applied to flexible substrates. One solution to the overlay challenges is imaging of two device layers in a single lithographic exposure. To enable the simultaneous patterning of two device layers, a new photoresist system was developed. Prior work on dual-tone photoresists introduced formulations capable of storing two independent images, but the reported systems are incompatible with the reactive ion etch processes commonly used today. This paper describes a dual-tone photoresist system that maintains the ability to store two independent latent images, distinguished by the incident exposure light wavelength, simultaneously remaining compatible with reactive ion etch image transfer processes.

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85.40.Hp	Lithography, masks and pattern transfer
81.65.Cf	Surface cleaning, etching, patterning

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Physical properties of individual anatase TiO₂ nanowires investigated by field emission in a transmission electron microscope

Jun Shen, Pascal Vincent, Nicholas P. Blanchard, Jimmy Nicolle, May Choueib, Stephen T. Purcell, Philippe Poncharal, Vincent Salles, and Arnaud Brioude

J. Vac. Sci. Technol. B 30, 011801 (2012); http://dx.doi.org/10.1116/1.3668121 (6 pages)

Online Publication Date: 13 December 2011

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The authors present studies on the field emission (FE) mechanism and the FE-induced transformation of individual anatase TiO₂ nanowires (NWs). The NWs were synthesized by electrospinning followed by calcination at 500 °C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of ∼100 nm in diameter were individually mounted at the apexes of tungsten tips for further physical characterization. The FE experiments were carried out in a TEM which allows the measurement of the FE current while simultaneously observing structural modifications leading to the NW’s destruction. For low currents (below 100 nA), we observe reproducible FE Fowler-Nordheim I/V characteristics. Higher currents (up to 1 μA) can be obtained but sudden destruction of the NW may take place. Our observations show that a thermally-activated transition occurs and leads to rapid re-crystallization phenomena and a variation of the FE characteristics. If not controlled, this transition leads to thermal runaway and sample destruction. The understanding of the destruction phenomena is a key parameter to further improve the FE performance of such nanowire cathodes.

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81.05.Hd	Other semiconductors
81.07.Gf	Nanowires
81.20.Ev	Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Ef	Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh	Other heat and thermomechanical treatments
85.45.Bz	Vacuum microelectronic device characterization, design, and modeling

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Modifying optical properties of GaN nanowires by Ga₂O₃ overgrowth

Yi-Kuang Lee, Henry Medina, and Po-Wen Chiu

J. Vac. Sci. Technol. B 30, 011802 (2012); http://dx.doi.org/10.1116/1.3668122 (4 pages)

Online Publication Date: 13 December 2011

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The authors report on the modification of optical properties of GaN nanowires by growing a thin Ga₂O₃ overlayer on GaN surface, forming a core/shell heterostructure. The GaN/Ga₂O₃ core/shell nanowires were formed first by the axial growth of GaN nanowires, followed by the radical growth of the Ga₂O₃ overlayer. The GaN core possesses single crystalline wurtzite structure, whereas the Ga₂O₃ shell layer is monoclinic polycrystalline. For the GaN/Ga₂O₃ core/shell nanowires, a pronounced blueshift of the Raman A₁(LO) mode was found, indicating a compressive stress on the core wire due to the lattice mismatch with the outer shell. This picture is also supported by the photoluminescence spectrum, in which the peak shifts to higher energy after the overgrowth of Ga₂O₃ on GaN.

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81.07.Gf	Nanowires
81.05.Hd	Other semiconductors
81.05.Ea	III-V semiconductors
78.67.Uh	Nanowires
78.55.Cr	III-V semiconductors
78.30.Fs	III-V and II-VI semiconductors

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Investigation of the factors determining the SIMS depth resolution in silicon-isotope multiple layers

M. Tomita, M. Koike, H. Akutsu, S. Takeno, Y. Kawamura, Y. Shimizu, M. Uematsu, and K. M. Itoh

J. Vac. Sci. Technol. B 30, 011803 (2012); http://dx.doi.org/10.1116/1.3669400 (12 pages)

Online Publication Date: 13 December 2011

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In order to identify their controlling factors, the depth resolution parameters for secondary ion mass spectrometry, which include the decay length and the standard deviation of the Gaussian function (also referred to as the depth resolution function), for silicon atoms in a silicon matrix with silicon-isotope multiple layers were investigated under oxygen (O2+) and cesium (Cs⁺) ion bombardments with a wide ion energy range (from 200 eV to 10 keV) and with several incident angles. The use of silicon-isotope multiple layers in this investigation eliminated the chemical segregation effect caused by the sample composition. Measures were also taken to prevent ripple formation on the sputtered sample surface. The obtained depth resolution parameters were proportional to E^1/2cos θ, where E is the primary ion energy per atom and θ is the incident angle relative to the surface normal. The relationships for decay length and standard deviation were different for the Cs⁺ ion, the O2+ ion with full oxidization, and the O2+ ion without full oxidization. The damage depth was measured by high-resolution Rutherford backscattering spectrometry and it was found that the relationships of the standard deviation versus damage depth depend only on the damage depth with a small dependence on the ion species (O2+/Cs⁺). The degree of mixing near the sputtered surface of thin silicon-isotope multiple layers bombarded by O2+/Cs⁺ ions was measured using laser-assisted atom probe analysis, and the relationship of the degree of mixing with the depth resolution parameters indicated that the decay length was degraded according to the degree of mixing. Atomic mixing/sputtering simulations revealed the factors determining the depth resolution parameters for secondary ion mass spectrometry. The standard deviation is found to be mainly degraded by the damage depth, which agrees with the results obtained by Rutherford backscattering spectrometry, whereas the decay length is mainly extended by the variance of the damage density profile, which is a parameter of the Gaussian function and governs the degree of mixing near the surface.

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79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh	Ion radiation effects
68.49.Sf	Ion scattering from surfaces (charge transfer, sputtering, SIMS)

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Nanofabrication of doped, complex oxides

Gordon H. Waller, Aaron Stein, and Jeremiah T. Abiade

J. Vac. Sci. Technol. B 30, 011804 (2012); http://dx.doi.org/10.1116/1.3669645 (6 pages)

Online Publication Date: 15 December 2011

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Complex oxides have many promising attributes, including wide band gaps for high temperature semiconductors, ion conducting electrolytes in fuel cells, ferroelectricity and ferromagnetism. Bulk and thin film oxides can be readily manufactured and tested however these physically hard and chemically inert materials cannot be nanofabricated by direct application of conventional methods. In order to study these materials at the nanoscale there must first be a simple and effective means to achieve the desired structures. Here we discuss the use of pulsed laser deposition at room temperature onto electron beam lithography defined templates of poly methyl methacrylate photoresist. Following a resist liftoff in organic solvents, a heat treatment was used to crystallize the nanostructures. The morphology of these structures was studied using scanning electron microscopy and atomic force microscopy. Crystallinity and composition as determined by x ray diffraction and photo-electron spectroscopy respectively is reported for thin film analogues of the nanostructured oxide. The oxide studied in this report is Nb doped SrTiO₃, which has been investigated for use as a high temperature thermoelectric material; however the approach used is not materials-dependent.

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81.07.-b	Nanoscale materials and structures: fabrication and characterization
81.15.Fg	Pulsed laser ablation deposition
81.16.Nd	Micro- and nanolithography
81.40.Gh	Other heat and thermomechanical treatments
61.46.-w	Structure of nanoscale materials
79.60.Bm	Clean metal, semiconductor, and insulator surfaces

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Barrier height determination of Au/Oxidized GaAs/n-GaAs using ballistic electron emission spectroscopy

Hailang Qin, Zhiqiang Liu, Cedric Troadec, Kuan Eng Johnson Goh, Michel Bosman, Beng Sheng Ong, Sing Yang Chiam, and Kin Leong Pey

J. Vac. Sci. Technol. B 30, 011805 (2012); http://dx.doi.org/10.1116/1.3675606 (4 pages)

Online Publication Date: 10 January 2012

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Ballistic electron emission spectroscopy (BEES) was used to determine the electron barrier height at the interface of Au and an oxidized GaAs film. Two thresholds were observed in the spectra. In a two-step procedure, we identified the first threshold at ∼1.4 eV, which we show arose from electron-hole pairs excited by photons emitted during scanning tunneling microscopy (STM), and the second threshold at ∼3.55 eV, which is attributed to the Au/oxidized-GaAs barrier. Our results demonstrate that the two-threshold behavior observed in BEES studies on metal/oxide samples is amenable to a physical model comprising of STM photocurrent and a metal/oxide interface barrier.

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73.40.Ns	Metal-nonmetal contacts
68.37.Vj	Field emission and field-ion microscopy
72.40.+w	Photoconduction and photovoltaic effects

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Roughness optimization of electron-beam exposed hydrogen silsesquioxane for immobilization of DNA origami

Faisal A. Shah, Kyoung Nan Kim, Marya Lieberman, and Gary H. Bernstein

J. Vac. Sci. Technol. B 30, 011806 (2012); http://dx.doi.org/10.1116/1.3676054 (6 pages)

Online Publication Date: 12 January 2012

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A novel way to immobilize deoxyribonucleic acid (DNA) origami on a conventional substrate using hydrogen silsesquioxane (HSQ) as a functionalized platform is demonstrated. An alternative approach to quantifying roughness of the HSQ surfaces for 2D DNA origami immobilization is also introduced. Effects of oxygen plasma treatment on the surface roughness and functionalization (for DNA origami immobilization) of exposed and developed HSQ patterns are characterized. Surface root mean square roughness of electron-beam exposed HSQ with various thicknesses is investigated and optimized down to 0.2 nm for ultrathin (sub-15 nm) HSQ patterns.

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81.05.Fb	Organic semiconductors
52.77.-j	Plasma applications
61.80.Fe	Electron and positron radiation effects
61.82.Pv	Polymers, organic compounds
81.65.-b	Surface treatments
68.35.bm	Polymers, organics

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Crystallization of Ge in SiO₂ matrix by femtosecond laser processing

Omer Salihoglu, Ulaş Kürüm, Halime Gul Yaglioglu, Ayhan Elmali, and Atilla Aydinli

J. Vac. Sci. Technol. B 30, 011807 (2012); http://dx.doi.org/10.1116/1.3677829 (5 pages)

Online Publication Date: 19 January 2012

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Germanium nanocrystals embedded in a siliconoxide matrix has been fabricated by single femtosecond laser pulse irradiation of germanium doped SiO₂ thin films deposited with plasma enhanced chemical vapor deposition. SEM and AFM are used to analyze surface modification induced by laser irradiation. Crystallization of Ge in the oxide matrix is monitored with the optic phonon at 300 cm⁻¹ as a function of laser fluence. Both the position the linewidth of the phonon provides clear signature for crystallization of Ge. In PL experiments, strong luminescence around 600 nm has been observed.

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68.55.ag	Semiconductors
52.77.Dq	Plasma-based ion implantation and deposition
61.80.Ba	Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx	Other solid inorganic materials
79.20.Ds	Laser-beam impact phenomena
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Ya	Chemistry of MOCVD and other vapor deposition methods

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Design and fabrication of GaN crystal ultra-small lateral comb-drive actuators

Takuma Tanae, Hidehisa Sameshima, and Kazuhiro Hane

J. Vac. Sci. Technol. B 30, 012001 (2012); http://dx.doi.org/10.1116/1.3668114 (8 pages)

Online Publication Date: 13 December 2011

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Ultra-small electromechanical comb-drive actuators made of GaN crystal were studied in order to apply them to optical micro-electromechanical systems. Using GaN crystals grown on Si substrates by metal-organic chemical vapor deposition, two kinds of electrostatic comb-drive actuators were designed and fabricated. In the fabrication, due to a residual stress of the grown crystal, the movable part of the actuator suffered considerable deformation depending on the growth conditions. The strain-stress issue of the grown crystal layer is discussed on the basis of lattice misfit and thermal expansion. To compensate for a convex deformation, crystallization tension of a thin HfO₂ film deposited on a GaN layer was investigated. The displacement of the actuator having dimensions of 52.2 μm in width and 105.4 μm in length was 1.3 μm at 70 V. Several variable systems will be feasible by combining the actuators monolithically with GaN opt-electronic devices. Future applications are also briefly discussed.

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85.85.+j	Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.60.Bt	Optoelectronic device characterization, design, and modeling
81.10.Bk	Growth from vapor
07.10.Cm	Micromechanical devices and systems
07.07.Tw	Servo and control equipment; robots

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Effect of ballast-resistor and field-screening on electron-emission from nanodiamond emitters fabricated on micropatterned silicon pillar arrays

N. Ghosh, W. P. Kang, J. L. Davidson, and S. Raina

J. Vac. Sci. Technol. B 30, 012201 (2012); http://dx.doi.org/10.1116/1.3674284 (5 pages)

Online Publication Date: 6 January 2012

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This paper describes the influence of ballast-resistor and field-screening on the electron field-emission behavior of nanodiamond emitter arrays fabricated on micropatterned silicon pillars. Arrays of 50 × 50 silicon pillars capped with nanodiamond with different ballast resistances and pillar separations have been fabricated on different silicon substrates as cathode for field emission testing. The goal of this study is to evaluate the fabrication method and electron emission characteristics in this configuration for field emission applications. The electron field emission results have been compared to observe the effect of the ballast resistive behavior and array spacing of micropatterned silicon pillars on the nanodiamond field emission behaviors.

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81.16.Rf	Micro- and nanoscale pattern formation
79.70.+q	Field emission, ionization, evaporation, and desorption
85.45.Db	Field emitters and arrays, cold electron emitters
73.63.-b	Electronic transport in nanoscale materials and structures

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Effects of proton irradiation energies on degradation of AlGaN/GaN high electron mobility transistors

Hong-Yeol Kim, Jihyun Kim, Lu Liu, Chien-Fong Lo, Fan Ren, and Stephen J. Pearton

J. Vac. Sci. Technol. B 30, 012202 (2012); http://dx.doi.org/10.1116/1.3676034 (4 pages)

Online Publication Date: 12 January 2012

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The authors report the proton energy dependence of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layers from 5 to 15 MeV at a fixed dose of 5 × 10¹⁵ cm⁻². All the samples degraded after proton irradiation. However, higher damage in dc electrical properties was observed at lower proton energies. Saturation currents at V_DS = 6 V and V_GS = 0 V reduced by 47% after proton irradiation at 5 MeV energy, but the reduction was less by 25% and 9% at 10 and 15 MeV, respectively. Similar trends were observed in other electrical properties [transconductance (g_m) and gate leakage currents]. This energy dependence from 5 to 15 MeV can be explained by the energy-dependent penetration depth of the proton. Protons with higher kinetic energy can penetrate deeper while creating less numbers of defects at shallow depths where the active layers of the HEMTs are located. These results are in good agreement with stopping and range of ions in matter results. The optimization of the AlGaN/GaN HEMT structure will be critical for space-borne applications where high fluxes of protons are encountered.

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85.30.Tv	Field effect devices
61.80.Jh	Ion radiation effects
61.82.Fk	Semiconductors

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Multi-phase model for reflection anisotropy spectra of copper phthalocyanine films on anisotropic silicon substrates

Falko Seidel, Li Ding, Ovidiu D. Gordan, and Dietrich R. T. Zahn

J. Vac. Sci. Technol. B 30, 012401 (2012); http://dx.doi.org/10.1116/1.3677823 (6 pages)

Online Publication Date: 23 January 2012

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Reflection anisotropy spectroscopy (RAS) and spectroscopic ellipsometry (SE) have extensively been applied to inorganic and organic structures and, because of the similarity of these two techniques, the evaluation procedure of RA spectra can be performed in a similar way as for SE. Especially for thin films, RA spectra are often strongly enhanced in the spectral region where optical interference occurs and the superposition of interference features can lead to an incorrect interpretation of RA spectra. By simulation of the origin of each RAS feature it is possible to distinguish interference from true film anisotropy. Also, the effect of surface roughness on the RA spectra is discussed.

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78.66.Qn	Polymers; organic compounds
68.35.bg	Semiconductors
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

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