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Nov 1999

Volume 17, Issue 6, pp. 2397-3452

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Fluorinated amorphous carbon films for low permittivity interlevel dielectrics

Jeremy A. Theil

J. Vac. Sci. Technol. B 17, 2397 (1999); http://dx.doi.org/10.1116/1.591102 (14 pages) | Cited 39 times

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The need to substitute SiO2 with low dielectric constant (κ) materials increases with each complementary metal–oxide–semiconductor process generation as interconnect RC delay, crosstalk, and power dissipation play an ever larger role in high-performance integrated circuits. Fluorinated amorphous carbon films (a-C:F,H) with low-κ properties (κ∼2.0–2.4) deposited by plasma-assisted chemical vapor deposition (CVD) techniques provide several advantages including low temperature processing, good gap fill capabilities, minimal moisture absorption, and simple implementation. Several deposition techniques have been examined, including high-density plasma and parallel-plate plasma-assisted CVD. In each case, it is possible to deposit a-C:F,H films with widely varying properties, such as κ and thermal stability. This has led to a good deal of confusion as to what is required to produce useful material. Results from many different sources are examined to develop a coherent picture of the relationships between deposition techniques, microstructural features, and macroscopic properties, and to summarize the scientific and technical challenges that remain for a-C:F,H implementation. The relationships between film deposition parameters such as applied substrate bias and film properties are presented in the discussion. In addition, x-ray photoelectron spectroscopy and network constraint theory are used to develop connections between microstructural and macroscopic properties, as well as to show how deposition parameters can be used to create a predictive model. This will demonstrate what process parameters are important in film formation. Finally, efforts to incorporate this material into integrated circuits, as well as measurements of the reliability and performance will be reviewed. © 1999 American Vacuum Society.
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61.43.Er Other amorphous solids
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Sz Deposition technology
85.40.Ls Metallization, contacts, interconnects; device isolation
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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Scanning tunneling microscopy of passivated Au nanocrystals immobilized on Au(111) surfaces

L. E. Harrell, T. P. Bigioni, W. G. Cullen, R. L. Whetten, and P.N. First

J. Vac. Sci. Technol. B 17, 2411 (1999); http://dx.doi.org/10.1116/1.591103 (6 pages) | Cited 10 times

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The surface mobility of alkanethiol-passivated Au nanocrystals on inert surfaces makes them challenging to image by scanning tunneling microscopy (STM). However, the potential for obtaining information on the density of states of these nanocrystals from tunneling spectroscopy measurements justifies the effort to find sample preparations that effectively immobilize them. We have explored the use of dithiol molecules as a means of strengthening the interaction between the substrate and the nanocrystal, with the goal of imaging isolated nanocrystals on a conducting substrate. Modifying the nanocrystals by substituting dithiol molecules into the passivation layer allowed the nanocrystals to bind strongly to the Au(111) surface. The formation of a self-assembled monolayer of xylenedithiol on the Au substrate allowed unmodified nanocrystals to more strongly adsorb to this modified surface. In both cases, isolated 1.7 nm nanocrystals were easily imaged by STM on Au(111), even at room temperature. These are significant steps toward the goal of obtaining high quality tunneling spectra from this class of materials. © 1999 American Vacuum Society.
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61.46.-w Structure of nanoscale materials
81.65.Rv Passivation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Field induced local oxidation of Ti and Ti/Au structures by an atomic force microscope with diamond coated tips

R. J. M. Vullers, M. Ahlskog, M. Cannaerts, and C. Van Haesendonck

J. Vac. Sci. Technol. B 17, 2417 (1999); http://dx.doi.org/10.1116/1.591104 (6 pages) | Cited 12 times

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We have investigated field induced local oxidation of thin Ti films with the tip of an atomic force microscope. Tips, which have been coated with a diamond layer to improve their wear resistance, are shown to have a much longer lifetime than conventional uncoated Si tips. We have studied the oxidation characteristics as a function of the applied tip-sample voltage and scanning speed for both diamond coated and uncoated tips. We find that the diamond coated tips result in a thinner oxide layer for the same voltage and scanning speed. The dependence of the oxidation process on the film thickness was studied for diamond coated tips. Thin films can be completely transformed into an oxide layer for a thickness up to 15 nm. Moreover, for these sufficiently thin films the measured ratio between the oxide height and the Ti film thickness is a constant. It is also possible to completely oxidize Ti films which cover Au islands, opening the way to fabricate more complicated structures. © 1999 American Vacuum Society.
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81.65.Mq Oxidation
81.05.Bx Metals, semimetals, and alloys
07.79.Lh Atomic force microscopes
73.23.-b Electronic transport in mesoscopic systems
68.60.Wm Other nonelectronic physical properties

In situ electrochemical atomic force microscopy study on Au(100)/Cd interface in sulfuric acid solution

Ruxandra Vidu and Shigeta Hara

J. Vac. Sci. Technol. B 17, 2423 (1999); http://dx.doi.org/10.1116/1.591105 (8 pages) | Cited 4 times

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The Cd electrodeposition on Au(100) in sulfuric acid solution was investigated by means of in situ electrochemical atomic force microscopy (EC-AFM) and long time polarization experiments. Initially, the Cd adlayer was formed at underpotentials (E=0.05 V/NHE) in a (√×√)R45°-Cd structure, which changed to a (1×1)-Cd structure at E=−0.45 V/NHE. Within the potential range from −0.3 to −0.45 V/NHE, a quick-alloying process was observed at the interface. The dynamic of the surface alloying was found to depend on polarization conditions. EC-AFM observation of the stripping process showed that the removing of the Cd bulk phase and the surface alloyed phase roughened the electrode surface. The mechanism that was proposed for surface alloying took into consideration the turnover process between Au and Cd atoms and the interdiffusion process of either Au or Cd atoms through the vacancy-rich surface alloy within the top layers. During bulk deposition at E=−0.49 V, Cd film was formed by a Stranski–Krastanov mechanism, with the Cd(0001) plane parallel to Au(100). © 1999 American Vacuum Society.
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81.05.Bx Metals, semimetals, and alloys
82.45.-h Electrochemistry and electrophoresis
68.35.Fx Diffusion; interface formation
81.65.-b Surface treatments

Vapor-deposited gold film formation on highly oriented pyrolitic graphite. A transition from pseudo-two-dimensional branched island growth to continuous film formation

B. Blum, R. C. Salvarezza, and A. J. Arvia

J. Vac. Sci. Technol. B 17, 2431 (1999); http://dx.doi.org/10.1116/1.591106 (8 pages) | Cited 10 times

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Growth of vapor-deposited gold islands on highly oriented pyrolitic graphite (HOPG) using evaporation rates in the range 0.01–0.1 nm/s has been investigated with ex situ scanning tunneling microscopy. Equivalent mean gold thickness and substrate temperature were varied from 1 to 20 ML and 333 to 358 K, respectively. Gold ad-islands several layers high grow both atop large HOPG terraces and along HOPG steps. Images show split and stable tip branched islands, depending on individual ad-island height and equivalent mean gold thickness. Initially, the diffusion of gold atoms towards island edges occurs via the HOPG surface, whereas soon thereafter it includes diffusion via gold terraces and steps. These two very dissimilar possibilities are due to both misfit strain variation with local gold-deposit thickness, and large differences in sticking probabilities of gold on HOPG and gold. Addition of gold to islands more than 20 layers high produces island-top flattening, branch coarsening with pronounced facetting, and tip stabilization, as a result of diffusion of gold from island tops to valleys and interbranch spaces. Extended flat areas present monoatomic-high triangular gold terraces. The transition from split to stable-tip branched islands is associated with a surface diffusion barrier which decreases with island height as a result of reduced lattice mismatch. Seemingly, early stages of branched gold island formation can be assimilated to a deposition, diffusion, and aggregation-type model that nucleates surface atom at island or terrace edges. Once flat gold terraces set in, the growth process can be described by an Edwards–Wilkinson-type model. Coalescence of gold ad-islands more than 20 layers high explains the well-known continuous films obtained in metal coaters under comparable growth conditions. © 1999 American Vacuum Society.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Fx Diffusion; interface formation
81.05.Bx Metals, semimetals, and alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)

Surface superstructure of Ar+-bombarded highly oriented pyrolytic graphite during recrystallization

B. An, S. Fukuyama, K. Yokogawa, and M. Yoshimura

J. Vac. Sci. Technol. B 17, 2439 (1999); http://dx.doi.org/10.1116/1.591107 (4 pages) | Cited 6 times

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The recrystallization process of highly oriented pyrolytic graphite (HOPG) surface bombarded by argon ions with an ion energy of 2.0–2.5 keV at doses of 2–5×1016 ions/cm2 was examined by scanning tunneling microscopy. The hillocks formed by the ion bombardment of HOPG coalesced to form larger grains with increasing annealing temperature. Three types of ringlike superstructures of (math×math)R30° of graphite were found on the curved surface of the grains after annealing in the temperature range of 1823–2673 K. The specimen surface became flat above 2773 K, where the ringlike superstructure disappeared and the triangular structure of graphite appeared in its place. The effect of the curved surface of the grains on the formation of the ringlike superstructure during graphitization is discussed. © 1999 American Vacuum Society.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Minimizing damage during focused-ion-beam induced desorption of hydrogen

H. Fuhrmann, A. Candel, M. Döbeli, and R. Mühle

J. Vac. Sci. Technol. B 17, 2443 (1999); http://dx.doi.org/10.1116/1.591108 (4 pages) | Cited 2 times

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The newly developed method of silicon surface structuring by local desorption of passivating hydrogen with a 30 keV Si+ focused ion beam has been investigated with respect to the damage induced by the irradiation. The substrate damage was analyzed by atomic force microscopy and thermal wave analysis. The measurements show that damage can be minimized if the substrate is heated to 200 °C during irradiation and dwell times below 20 μs are used for the exposure, even at a dose of 2×1015 cm−2, which exceeds the minimum dose required to define a feature by a factor of 10. The irradiated surfaces remain flat after KOH etching, the surface roughness being smaller than 0.3 nm for all samples. © 1999 American Vacuum Society.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Atomic force microscopy of the topochemical photopolymerization of diolefin crystals

Qingdao Zeng, Chen Wang, Chunli Bai, Yan Li, and Xinjian Yan

J. Vac. Sci. Technol. B 17, 2447 (1999); http://dx.doi.org/10.1116/1.591109 (5 pages) | Cited 4 times

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The formation of regular nanostructures by photopolymerization of three diolefin derivative crystals, P2VB, DSP, and p-CPAEt, is investigated using atomic force microscopy (AFM) and known crystal packing data. AFM reveals that the crystal face (100) and (010) of P2VB exhibit volcanoes, whereas (100) and (010) of DSP give floelike structures. The main face and long side face of p-CPAEt give rise to volcanoes. All of those are guided by the crystal structure. Molecular interpretations of the AFM features of P2VB and DSP are given. © 1999 American Vacuum Society.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
61.46.-w Structure of nanoscale materials

Scratching on polystyrene thin film without bumps using atomic force microscopy

Futoshi Iwata, Tarou Matsumoto, Ryuhei Ogawa, and Akira Sasaki

J. Vac. Sci. Technol. B 17, 2452 (1999); http://dx.doi.org/10.1116/1.591110 (5 pages) | Cited 8 times

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Polystyrene (PS) thin film modified with a novel ultrasonic scratching method has been studied using an atomic force microscope (AFM). Ultrasonic scratching can be realized by a combination of an AFM and a quartz crystal resonator (QCR). The PS thin film was deposited on the surface of an AT-cut QCR which oscillates with mechanical shear deformation at its resonant frequency (6.5 MHz) with amplitude of a few nm. The oscillating surface is scratched with the AFM’s diamond tip to generate an effective cutting force. Scratching without a QCR oscillation forms bumps on the PS surface, which is known well to be a unique phenomenon of scratched polymer surfaces. However, ultrasonic scratching can result in the carving of PS thin films without the formation of bumps. The depressed bottom carved by ultrasonic scratching is flat in comparison with that scratched without surface oscillations. Furthermore, on the previously modified area of ultrasonic scratching, bumps are not formed, even after overlapping of the scratching without surface oscillations. © 1999 American Vacuum Society.
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62.20.Qp Friction, tribology, and hardness
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Near-field polarization states and optical images in transmission mode through different surface structures

S. Wang

J. Vac. Sci. Technol. B 17, 2457 (1999); http://dx.doi.org/10.1116/1.591111 (5 pages)

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We provide a theoretical study of the near-field optical image of a homogeneous dielectric surface with deterministic sub-wavelength structures. Numerical simulations for different shapes of the sample are performed at constant-height mode with normal incidence. Near-field polarization states have been calculated by analyzing the difference of the transmitted intensities of p- and s-polarized light. We show that the near-field intensity depends more stronger on the feature form than the feature size. However, the polarization property is more sensitive to the shape of the sample rather than the distance of detection. © 1999 American Vacuum Society.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Fc Near-field scanning optical microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
42.25.Ja Polarization
02.60.Cb Numerical simulation; solution of equations

Nanometric aperture arrays fabricated by wet and dry etching of silicon for near-field optical storage application

M. B. Lee, N. Atoda, K. Tsutsui, and M. Ohtsu

J. Vac. Sci. Technol. B 17, 2462 (1999); http://dx.doi.org/10.1116/1.591112 (5 pages) | Cited 2 times

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We fabricated nanometric aperture arrays in order to apply to an optical probe in high-density near-field optical storage for increase of data-transmission rate. The aperture arrays were fabricated by forming concave pyramidal grooves on a silicon-on-insulator wafer with electron beam lithography and wet anisotropic etching. Modification of the apex shape of the grooves by re-oxidation and subsequent reactive ion dry etching was able to increase the uniformity of the aperture size remarkably. The light transmission efficiency of the fabricated apertures was measured to be ∼10−3 when the aperture size was 100 nm, which was higher than that of a conventional optical fiber probe by several orders of magnitude. © 1999 American Vacuum Society.
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42.79.Vb Optical storage systems, optical disks
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Ultrahigh density data storage in an organic film with a scanning tunneling microscope

S. M. Hou, X. Y. Zhao, C. Yang, Z. Q. Xue, W. J. Yang, and H. Y. Chen

J. Vac. Sci. Technol. B 17, 2467 (1999); http://dx.doi.org/10.1116/1.591113 (4 pages) | Cited 1 time

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A nanometer-scale recording technique was demonstrated on N-(3-nitrobenzylidene)–p-phenylenediamine (NBPDA) organic thin films with a scanning tunneling microscope (STM). NBPDA thin films were fabricated by vacuum thermal deposition. The results of ultraviolet-visible absorption and infrared transmission spectra showed that the structure of the NBPDA film was the same as that of NBPDA crystal. An atomic force microscope was utilized to characterize the surface morphology of the NBPDA film. Data were recorded by applying voltage pulses between the tip and the substrate. The current–voltage characteristics measured by the STM indicated that the local electrical property changed from an insulating property into a metallic property after the data were written. Data marks, 1.4 nm in diameter, corresponded to a data storage density of 1012 bits/cm2. A preliminary calculation was presented to explain the recording mechanism. © 1999 American Vacuum Society.
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07.79.Cz Scanning tunneling microscopes

Fabrication and magneto-transport and SQUID measurements of submicron spin-valve structures

Y. D. Park, D. Temple, K. B. Jung, D. Kumar, P. H. Holloway, and S. J. Pearton

J. Vac. Sci. Technol. B 17, 2471 (1999); http://dx.doi.org/10.1116/1.591114 (5 pages)

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Submicron Ni0.8Fe0.2/Cu/Co spin valves and Co/Cu pseudo spin valves with widths ranging from 200 to 0.5 μm have been realized by direct deposition and liftoff. The resulting configurations were structurally characterized by atomic force microscope and cross-sectional transmission electron microscopy. Transport and magnetic properties of arrays of these spin-valve structures were studied using superconducting quantum interference device magnetometry. Magnetic measurements carried out on several spin-valve structures showed that both coercivity and field at which maximum magnetoresistance (MR) occurs increase with decrease in widths of the spin valves. Comparison of the results obtained from the magnetometry and transport measurements indicated the existence of an offset between the coercive field and field of maximum MR. Resistance versus temperature measurements for varying linewidth show a minimal shift in peak temperature, indicating that processing effects are minimal. © 1999 American Vacuum Society.
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75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Nanoscale elemental imaging of semiconductor materials using focused ion beam secondary ion mass spectrometry

F. A. Stevie, S. W. Downey, S. R. Brown, T. L. Shofner, M. A. Decker, T. Dingle, and L. Christman

J. Vac. Sci. Technol. B 17, 2476 (1999); http://dx.doi.org/10.1116/1.591115 (7 pages) | Cited 8 times

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The semiconductor industry demands elemental information from ever smaller regions. The sensitivity of secondary ion mass spectrometry, coupled with the lateral resolution of a focused ion beam, can provide nanoscale elemental data that are competitive with that from other analytical techniques. Ion images of the sidewalls in repetitive semiconductor features tilted to present a large surface area have shown boron contamination after an etch process. The boron is removed by a specific cleaning step. Spot defect analysis was enhanced by the use of mass spectra that provide information on a range of elements before the defect is removed by sputtering. Ion implanted samples were analyzed in cross section and the implant shape detected. Summation of the secondary ion counts in the implant cross section over a few micrometers resulted in detection limits below 0.1 at. %. Implantation profiles have been detected for Al, Cr, Na, Li, and K without the aid of secondary ion enhancing species, such as oxygen or cesium. © 1999 American Vacuum Society.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.S- Impurities in crystals
07.75.+h Mass spectrometers
85.40.Ry Impurity doping, diffusion and ion implantation technology

Direct current and pulsed operation of contaminated liquid metal ion sources

R. T. Olson and J. A. Panitz

J. Vac. Sci. Technol. B 17, 2483 (1999); http://dx.doi.org/10.1116/1.591116 (5 pages)

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Gallium liquid metal ion sources (LMISs) have been exposed to common gas and liquid phase laboratory and vacuum system contaminants. Minor changes in the direct current and pulsed operation of the LMISs were observed after contaminant exposure. Time-of-flight mass analysis of the ion emission revealed that contaminant species are primarily field evaporated with the gallium substrate. Low vapor pressure contaminants have been observed to constitute a significant portion of the total emitted ion current. © 1999 American Vacuum Society.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

Comparison of metrology methods for quantifying the line edge roughness of patterned features

C. Nelson, S. C. Palmateer, A. R. Forte, and T. M. Lyszczarz

J. Vac. Sci. Technol. B 17, 2488 (1999); http://dx.doi.org/10.1116/1.591117 (11 pages) | Cited 22 times

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Comparisons are made of two atomic force microscopes in different modes of operation, and two scanning electron microscopes, one high and one lower resolution for quantifying the edge roughness of patterned features in resist and silicon. Definitions of the edge roughness magnitude and spatial frequency are given. For each metrology method, the parameters that limit the edge roughness measurement and how they compare to the parameters that limit the critical dimension measurement are addressed. An attempt to quantify the edge roughness spatial frequency is also discussed. For the two best metrology methods the repeatability of the measurements was determined, and measurements were made to understand the correlation between them. © 1999 American Vacuum Society.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Lh Atomic force microscopes

Focus drilling and attenuated phase shift mask for subwavelength contact window printing using positive and negative resists

S. Pau, L. E. Trimble, J. W. Blatchford, G. P. Watson, J. Frackoviak, R. Cirelli, and O. Nalamasu

J. Vac. Sci. Technol. B 17, 2499 (1999); http://dx.doi.org/10.1116/1.591118 (8 pages) | Cited 2 times

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We have investigated the process latitude and resolution limit of printing contact windows using a high numerical aperture KrF stepper and attenuated phase shift mask (APSM). We show that both positive and negative resists can be used depending on the size of the window on the mask. The advantages and disadvantages of using the positive and negative resists are presented. A combination of APSM and focus drilling are shown to extend the focus latitude of subwavelength window printing. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer

Electron beam lithography process for T- and Γ-shaped gate fabrication using chemically amplified DUV resists and PMMA

Y. Chen, D. Macintyre, and S. Thoms

J. Vac. Sci. Technol. B 17, 2507 (1999); http://dx.doi.org/10.1116/1.591119 (5 pages) | Cited 10 times

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A new process has been developed to fabricate T-shaped gates and Γ-shaped gates for high performance metal–semiconductor field effect transistors and high electron mobility transistors using a bilayer of Shipley UVIII DUV resist and poly(methylmethacrylate). The two resists are separated by a 20–30 nm thick layer of aluminum and after patterning by electron beam lithography a two-stage development technique is used to remove the aluminum and to produce well-defined resist profiles. The process can be used to fabricate T-shaped and Γ-shaped gates with footwidth sizes as small as 50 nm and headwidth to footwidth ratios in excess of 40:1 for T gates and 35:1 for Γ gates. The ability to fabricate gates with these dimensions arises from the fact that the UVIII resist is considerably more sensitive to electron beam exposure than PMMA. Further benefits derived from using a UVIII: PMMA bilayer are better control of footwidth dimensions and shorter electron beam patterning times compared to bilayers of PMMA with copolymers of PMMA. This article describes process optimization and the relationship between feature size and exposure dose. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Low-energy electron-beam effects on poly(methyl methacrylate) resist films

V. M. Bermudez

J. Vac. Sci. Technol. B 17, 2512 (1999); http://dx.doi.org/10.1116/1.591134 (7 pages) | Cited 7 times

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The effects of low-energy electron irradiation (10–50 eV, up to ∼2×1017 e cm−2) on thin films of poly(methyl methacrylate) (PMMA), deposited on air-exposed Al, have been studied in situ as a function of temperature (∼200–300 K) using polarization-modulated infrared reflection absorption spectroscopy. Near 300 K damage is seen in the form of a loss of material, as shown by a decrease in the intensity of the entire PMMA spectrum. At low temperature, in addition to damage, evidence is seen for a radiation-induced change in chain configuration leading to an increased interaction between ester groups and the Al surface. This configuration is unstable and is removed by annealing to ∼300 K.
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85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
61.80.Fe Electron and positron radiation effects
61.82.Pv Polymers, organic compounds
78.66.Qn Polymers; organic compounds
78.30.Jw Organic compounds, polymers

Application of a thin-resist process for KrF imaging to 130 nm device fabrication

Tsukasa Azuma, Kenji Chiba, Daisuke Kawamura, Seiro Miyoshi, Tohru Ozaki, and Hiroyoshi Kageyama

J. Vac. Sci. Technol. B 17, 2519 (1999); http://dx.doi.org/10.1116/1.591120 (5 pages) | Cited 2 times

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A practical bilayer bottom antireflective coating (BARC) process, consisting of an upper conventional organic film and a lower amorphous-Si blackout film, is introduced to realize highly antireflective performance and efficient pattern-transfer performance simultaneously. The application of a thin-resist process for KrF imaging to 130 nm device fabrication is also investigated including a practical pattern-transfer process, especially in the gate layer and the metal-wiring layer. It is demonstrated that no standing-wave effects in the resist are observed due to the effective bilayer BARC structure; furthermore, the resist patterns, which are 215 nm thick, are successfully transferred to the substrates in the gate layer and the metal-wiring layer. Finally, experimental and simulation results suggest that the thin-resist process, in combination with the practical bilayer BARC process using KrF imaging featuring a numerical aperture of 0.68 and a partial coherency of 0.75 with a 2/3 annular aperture, could guarantee the early stage of 1 Gb dynamic random access memory device fabrication. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.79.Wc Optical coatings

Improvement of InGaP/GaAs heterointerface quality by controlling AsH3 flow conditions

Yoshino K. Fukai, Fumiaki Hyuga, Takumi Nittono, Kazuo Watanabe, and Hirohiko Sugahara

J. Vac. Sci. Technol. B 17, 2524 (1999); http://dx.doi.org/10.1116/1.591121 (6 pages) | Cited 6 times

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Heterointerfaces between disordered InGaP on GaAs, whose conduction band offset, ΔEc, is 0.2 eV, can be improved and have less interface charges by controlling the AsH3 cover time and flow rate at the growth interval from GaAs to InGaP by metalorganic chemical vapor deposition. A small AsH3 cover of 5 cc (0.05 min with 100 cc/min) creates a low interface charge density, σ, of 6.4×1010 cm−2. Extending the AsH3 cover to only 25 cc increases σ by one order, even though AsH3 is purged by PH3 for a rather long time after being covered. Interface charges are confirmed to be donors whose energy level is near the conduction band edge. These results show that excess As on the GaAs surface enhances the formation of donor-like defects in the InGaP layer. An As-poor GaAs surface is essential in order to achieve high-quality InGaP/GaAs heterointerfaces. © 1999 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Influence of growth temperature of InAsP/InP strained multiple quantum wells grown by metalorganic chemical vapor deposition

Chong-Yi Lee, Hung-Pin Shiao, Meng-Chyi Wu, and Chyuan-Wei Chen

J. Vac. Sci. Technol. B 17, 2530 (1999); http://dx.doi.org/10.1116/1.591122 (6 pages) | Cited 2 times

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In this article, we report the influence of growth temperature on the luminescent and structural properties of InAsyP1−y/InP strained multiple quantum wells (SMQWs) and strained single quantum wells (SSQWs) grown by metalorganic chemical vapor deposition (MOCVD). The strained quantum wells are characterized by high-resolution transmission electron microscope (TEM), photoluminescence (PL), and double-crystal x-ray diffraction (DC-XRD). An AsH3/(AsH3+PH3) gas flow ratio of 0.50% and 1.48% at 580 and 650 °C growth temperatures, respectively, will result in an InAsP layer with y=0.3 solid composition. The experimental PL emission energies at 10 K at different well thicknesses for the InAsyP1−y/InP SSQWs grown at 580 and 650 °C are in well agreement with the trend of the calculated curves. The TEM lattice image of an InAsP/InP SSQW grown at 580 °C on the order of two monolayers has been demonstrated. The InAsP/InP SSQW structure grown at 580 °C appears to be extremely abrupt, uniform, free of misfit dislocations, and narrow PL linewidth. Besides, the growth of InAsP/InP SMQWs at 580 °C maintains its structural integrity throughout the deposition sequence with smooth interface and well-defined periodicity. However, the InAsP/InP SSQWs or SMQWs exhibit an adverse property at 650 °C growth temperature. From the above results, the lower growth temperature is necessary for the InAsP/InP SMQW growth by MOCVD. © 1999 American Vacuum Society.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Quantum mechanical tunneling through a biased double-cascaded barrier

J. M. Mohaidat and Riyad N. Bitar

J. Vac. Sci. Technol. B 17, 2536 (1999); http://dx.doi.org/10.1116/1.591123 (4 pages)

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We provide a detailed study of the leakage tunneling current through two cascaded-barrier structures with different potentials sandwiched between a metal and substrate electrodes. The current–voltage (I–V) characteristics were obtained by solving the time-dependent Schrödinger equation. The structure Al/Ta2O5/SiO2/n+–Si is taken as an example. The effects of the SiO2 barrier thickness and the gate biasing polarity are studied. We found that the effect of the SiO2 barrier thickness, along with positive gate biasing was to slightly reduce the leakage current value. However, the effect of the SiO2 layer thickness, along with negative gate biasing, was to significantly change the I–V characteristics. The computed I–V characteristics were plotted according to the Fowler–Nordheim tunneling expression to check on its adequacy for cascaded potentials. Such plots will also be valuable in evaluating experimental findings. Results are compared with recently published experimental results on Ta2O5 thin films on Si substrates. © 1999 American Vacuum Society.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
73.23.Hk Coulomb blockade; single-electron tunneling

Temperature-graded InAlAs buffers applied on InGaAs/InAlAs/InP high electron mobility transistor heterostructures

J. Arbiol, F. Peiró, A. Cornet, K. Michelakis, and A. Georgakilas

J. Vac. Sci. Technol. B 17, 2540 (1999); http://dx.doi.org/10.1116/1.591124 (5 pages)

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In this work we studied the possibility of improving InGaAs/InAlAs-on-InP high electron mobility transistor (HEMT) devices by using temperature-graded InAlAs buffer layers with growing temperatures in the range of Tg=250–560 °C. Our specimens were grown by molecular beam epitaxy and we analyzed them using plane view and cross-sectional transmission electron microscopy, atomic force microscopy, scanning electron microscopy and Hall effect measurements. We found that growth at the optimum temperature (Tg=530 °C) of a thin InAlAs buffer sublayer between the InP substrate and the thick InAlAs buffer layer (grown at low or high Tg) can dramatically improve the crystalline quality of our HEMT devices. Therefore the growth temperature of the buffer could be used as engineering parameter to tailor the electronic properties of InAlAs layers without interfering with the layers’ crystalline quality, already assured by the first optimized nanometers. © 1999 American Vacuum Society.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors

Depth-resolved electron-excited nanoscale-luminescence spectroscopy studies of defects near GaN/InGaN/GaN quantum wells

T. M. Levin, G. H. Jessen, F. A. Ponce, and L. J. Brillson

J. Vac. Sci. Technol. B 17, 2545 (1999); http://dx.doi.org/10.1116/1.591125 (8 pages) | Cited 13 times

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We have measured the energies, relative intensities, and spatial distribution of deep level defect transitions near GaN/InGaN/GaN quantum well structures using low-energy electron-excited nanoscale-luminescence (LEEN) spectroscopy. Results obtained with electron excitation energies as low as 100 eV provide evidence on an incremental, 10–20 nm scale for defects within the GaN confinement layer, their variation with distance from the quantum well, and their electronic quality relative to the GaN substrate. The InGaN quantum well and GaN near-band-edge luminescence intensities exhibit strong variations as a function of excitation depth. Combined with a model of energy-dependent penetration, diffusion, and recombination, these variations indicate a value of 25–28 nm for the minority carrier diffusion length within the GaN confinement layer. Depth-dependent spectra also reveal the presence of cubic GaN phase formation at the InGaN/GaN substrate interface of a relatively In-rich quantum well structure. The contrast in LEEN features between structures of two different InGaN quantum well compositions demonstrates the effect of growth composition on local state formation. © 1999 American Vacuum Society.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Correlation between agglomeration of a thin film and reflow filling in a contact hole for sputtered Al films

S. Shingubara, H. Kotani, H. Sakaue, F. Nishiyama, and T. Takahagi

J. Vac. Sci. Technol. B 17, 2553 (1999); http://dx.doi.org/10.1116/1.591126 (6 pages) | Cited 3 times

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Al reflow filling in contact holes by annealing after Al deposition at room temperature was investigated with relation to agglomeration properties of very thin films. A strong correlation between filling achievement and agglomeration property was observed when the underlayer TiN film property was changed. When rapid thermal nitridation (RTN) was carried out after reactive sputtering of TiN, excellent filling in submicron contact holes was achieved at annealing temperatures around 400 °C for the case of thick Al film, and agglomeration into small islands was observed for thin Al films. The activation energy of atomic mass transport for the filling process was 0.36 eV, which suggests a surface diffusion dominated filling process. On the other hand, when no RTN was carried out for TiN, reflow filling was achieved at temperatures around 600 °C which were close to the melting point of Al, and agglomeration into islands in thin films was suppressed at 400 °C. The activation energy of the latter case was 0.90 eV, which was between those of lattice diffusion and grain boundary diffusion. The correlation between filling achievement and agglomeration is ascribed to a large surface diffusion atomic flux in the case with RTN. © 1999 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

Low resistance small metal contact for high temperature application

J. S. Kim, W. T. Kang, W. S. Lee, B. Y. Yoo, Y. C. Shin, T. H. Kim, K. Y. Lee, Y. J. Park, and J. W. Park

J. Vac. Sci. Technol. B 17, 2559 (1999); http://dx.doi.org/10.1116/1.591127 (6 pages)

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A reliable small metal contact (∼0.18 μm) withstanding high temperature post-thermal budget (∼800 °C for 30 min) is developed for a bit-line (BL) contact of gigabit scaled dynamic random access memories with capacitor-over BL structure. Cobalt (Co) salicidation on the source/drain regions is indispensable to have low BL contact resistance (Rc). The CoSix layer under the contact hole prevents the contact liner (Ti) from reacting with the sub-silicon. Thus, TiSix agglomeration as well as dopant-TiSix interaction is suppressed even with relatively high postannealing temperature. Thin SiN layer on the CoSix is an effective etch stopper during contact etch and protects the thin CoSix layer from the etch damage. Use of an Ar+ soft inductively coupled plasma cleaning instead of the wet chemical cleaning after contact etch is another key factor to attain a reliable BL contact process. The low Rc and contact leakage are ensured when ion–metal–plasma Ti/TiN liner is utilized. © 1999 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Microstructure of concentric ring patterns on Ta/Si(100)

H. Y. Sheng, D. Fujita, Z. C. Dong, H. Okamoto, T. Ohgi, and H. Nejoh

J. Vac. Sci. Technol. B 17, 2565 (1999); http://dx.doi.org/10.1116/1.591128 (5 pages) | Cited 1 time

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We observed concentric ring patterns on a Ta film deposited on Si(100) after thermal treatments of annealing at 900 °C for 24 h, followed by flashing at 1300 °C for a few seconds in an ultrahigh vacuum. The diameters of the ring pattern range from a few tens of micrometers to several hundred micrometers. Atomic force microscopy studies indicate a height of about 100 nm for the rings. Auger electron spectroscopy analyses show that the TaSi2 layer is formed on the Si surface during heating and that the silicide layer is about four times thicker than the as-deposited Ta film. © 1999 American Vacuum Society.
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68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Characterization of CoSi2 formation by x-ray photoelectron spectroscopy

Jin Zhao, Clive M. Jones, and Derrick M. Poirier

J. Vac. Sci. Technol. B 17, 2570 (1999); http://dx.doi.org/10.1116/1.591129 (5 pages) | Cited 2 times

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Formation of CoSi2 in the conversion sequence of pure Co, CoSi, and CoSi2 was characterized using x-ray photoelectron spectroscopy (XPS). With pure Co deposited on single crystalline Si wafers and capped by Ti thin film, the wafers were rapid thermal annealed (RTA) at 470 °C for 60 s so as to convert Co to CoSi. These wafers were then stripped with APM (NH4OH/H2O2/H2O) and SPM (H2SO4/H2O2), followed by RTA at 700 °C for 60 s to obtain final CoSi2. XPS was used to determine the chemical composition of these thin films and the Co Auger parameter was continuously monitored along with ion sputtering to provide chemical state depth profile. After the RTA at 470 °C, the XPS depth profile shows that a mixed Ti/Co/Si region exists between the CoSi film and Ti cap. After the strip, the Ti cap and Ti/Co/Si region were removed. The uniformed CoSi2 film was present after the RTA at 700 °C. The Co Auger parameters of pure Co, CoSi, and CoSi2 are 1552.1, 1551.6, and 1551.4 eV, respectively. Monitoring the Co Auger parameter along with the ion sputtering depth profile indicates that CoSi2 has the most stable cobalt chemical state after RTA at 700 °C. The interface region with film composition of Co/Si ratio less than 1:2 is a mixture of CoSi2 and pure Si. For the interface regions with film composition of Co/Si ratio less than 1:2 of the as-deposited Co wafer and the wafer after RTA at 470 °C, the Co Auger parameters are 1551.2 eV, which suggests that a possible distinctive cobalt chemical state exists. © 1999 American Vacuum Society.  
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68.35.Fx Diffusion; interface formation
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.Cc Kinetics of defect formation and annealing

Tribological behavior of TiC/DLC multilayers prepared on Ti–6Al–4V alloy by plasma-based ion implantation

Hongbing Ji, Lifang Xia, Xinxin Ma, Yue Sun, and Mingren Sun

J. Vac. Sci. Technol. B 17, 2575 (1999); http://dx.doi.org/10.1116/1.591130 (6 pages) | Cited 2 times

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Plasma-based ion implantation (PBII) of carbon (time 1–3 h) and subsequent glow discharge deposition of carbon produced TiC/DLC multilayers on Ti–6Al–4V samples (TiC second phase formed in the near surface region plus DLC surface layers). The as-modified samples showed higher hardness than the uncoated sample especially at low plastic penetrations in the order of the 1, 2, and 3 h carbon implantation, but had brittle wear appearances. When the implantation time was increased, the brittleness increased, hence the tribological properties in most cases deteriorated. A tribofilm transferred from a disk wear surface was formed on the wear surface of a counterbody made of bearing steel AISI 52100, lowering the friction coefficient, and reducing the ball wear. When the wear load was decreased and sliding speed increased, the function of the tribofilm became more important; the friction decreased, and the wear properties improved, with a stable friction coefficient ranging from 0.1 to 0.2. But when the counterbody AISI 52100 was changed to Ti–6Al–4V modified as the disk, the tribological behavior surprisingly deteriorated, with wear changing from only disk to both disk and ball abrasive dominated, and it is probably the transferred disk wear debris that caused wear weight increases of the counterbody Ti–6Al–4V. © 1999 American Vacuum Society.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
61.72.up Other materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Novel process integration for reduction of subquarter-micron contact resistance

Victor Ku

J. Vac. Sci. Technol. B 17, 2581 (1999); http://dx.doi.org/10.1116/1.591131 (3 pages)

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In this article, etching of subquarter-micron contact holes with a film structure of silicon dioxide (SiO2)/silicon nitride (Si3N4)/silicide (TiSix) in dual-frequency capacitively coupled plasmas is investigated. The etch process scheme here uses a highly selective chemistry to remove SiO2 film first, then the process switches to another chemistry with high etch selectivity of Si3N4-to-TiSix. The author found that the polymer film deposited inside contact holes during SiO2 etching severely degraded the selectivity of Si3N4-to-TiSix. This can cause open or high contact resistance. Different process integration schemes with the goal of increasing the etch selectivity of Si3N4-to-TiSix were initiated and developed. Electrical parametric data of contact chain resistance will be presented. © 1999 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
81.65.Cf Surface cleaning, etching, patterning

Experimental and analytical study of seed layer resistance for copper damascene electroplating

E. K. Broadbent, E. J. McInerney, L. A. Gochberg, and R. L. Jackson

J. Vac. Sci. Technol. B 17, 2584 (1999); http://dx.doi.org/10.1116/1.591132 (12 pages) | Cited 11 times

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Copper electroplating for integrated circuit damascene applications typically relies on a thin, conductive seed layer to promote nucleation of feature fill and acceptable overall thickness distribution during deposition. Important to the charge-transfer exchange process occurring at the wafer surface is the potential drop within the seed layer during the early stages of plating. The effective damascene surface area, seed layer coverage, and overall resistance of thin Cu films are examined via modeling and experimental measurements. The current-carrying capability of seed-metallized trenches is calculated in terms of an effective trench resistivity and used to compare physical vapor deposition (PVD) methods with chemical vapor deposition (CVD). For a nominal 2:1 aspect ratio trench, the modeled CVD seed resistance was found to be 5× lower than that of ionized PVD and about 2.8× lower than that of ionized PVD with resputter. Wafer-level resistance probing is introduced as a useful means to assess global differences in seed layer resistance on actual patterned substrates. Initial measurements on low-density patterns confirm that PVD seed films exhibit larger increases (+24% to 78%) in resistance than CVD films (+11%) when compared to their respective planar counterparts. Results indicate that seed resistance levels on patterned damascene substrates can be significantly larger than on planar monitor wafers—an important implication for the Cu plating manufacturing process. © 1999 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.05.Bx Metals, semimetals, and alloys
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Pq Electrodeposition, electroplating
81.15.Cd Deposition by sputtering

Effect of material variations on performance of double-recessed gate power pseudomorphic high electron mobility transistors in monolithic microwave and millimeter wave integrated circuit applications

T. Hussain, P. Chu, C. P. Wen, M. Circle, A. Gomez, T. Midford, and T. Cisco

J. Vac. Sci. Technol. B 17, 2596 (1999); http://dx.doi.org/10.1116/1.591133 (4 pages)

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We report the effect of start epi-material variability on the performance of double-recessed power pseudomorphic high electron mobility transistors. Variation in channel-recess depth, which is related to variation in the start material, is critically linked to rf performance of monolithic microwave and millimeter wave integrated circuit high power amplifiers. For high yield, it is important to control the channel recess, which in turn has implications on acceptable variation in epi-material. Design tweaks can relax channel-recess tolerance limits, but it is still important to account for material variation. © 1999 American Vacuum Society.
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85.30.Tv Field effect devices
84.40.Lj Microwave integrated electronics

Direct epitaxial growth of submicron-patterned SiC structures on Si(001)

Gyu-Chul Yi, G. Eres, and D. H. Lowndes

J. Vac. Sci. Technol. B 17, 2600 (1999); http://dx.doi.org/10.1116/1.591029 (3 pages)

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We report on the direct epitaxial growth of submicron-patterned SiC structures on Si(001) substrates using supersonic molecular jet epitaxy and resistless e-beam lithography. Prior to SiC film growth, an electron beam was scanned on hydrogen-passivated Si substrates in order to produce silicon oxide lines with widths ⩾60 nm. The SiC nucleation and growth rates were significantly reduced on the oxidized regions during the subsequent supersonic jet epitaxial growth of SiC, which yielded epitaxial, submicron-patterned SiC films. The effects of the growth temperature and e-beam dose on the SiC growth and pattern linewidth are discussed. © 1999 American Vacuum Society.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors
85.40.Sz Deposition technology
85.40.Hp Lithography, masks and pattern transfer

Finite-element calculations of mechanical stresses induced by water adsorption/desorption in silicate glasses

Thomas Hoffmann, Philippe LeDuc, and Vincent Senez

J. Vac. Sci. Technol. B 17, 2603 (1999); http://dx.doi.org/10.1116/1.591033 (7 pages) | Cited 2 times

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The mechanical stresses induced by adsorption or desorption of water from various dielectric films (vitreous silicate glass, phosphosilicate glass, borophosphosilicate glass, and spin on glass) are analyzed in terms of two-dimensional finite-element simulations. For this, a new model that predicts the stress induced by the adsorption or desorption of water in the films (i.e., the extrinsic stress) has been added to a general algorithm dedicated to the calculation of stresses in silicon processes. This model was calibrated for (un)doped silicate glasses and spin on glass. Thanks to this work, a mechanical study and optimization of back-end processes, including all sources of stress, are now available. It is shown that the stresses developed in densified spin on glass can be very high and are likely to degrade the reliability of devices planarized by these techniques. © 1999 American Vacuum Society.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
02.70.Dh Finite-element and Galerkin methods

Monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using remote plasma processing: Formation of stacked “N–O–N” gate dielectrics

H. Niimi and G. Lucovsky

J. Vac. Sci. Technol. B 17, 2610 (1999); http://dx.doi.org/10.1116/1.591034 (12 pages) | Cited 41 times

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A low thermal budget approach to monolayer-level controlled incorporation of nitrogen in ultrathin gate dielectrics using 300 °C, remote plasma processing is discussed. Incorporation of approximately 1 ML of nitrogen at the Si–SiO2 interface in an “N–O” structure has been achieved by remote plasma-assisted oxidation of the Si surface followed by N2/He remote plasma nitridation, each at a process pressure of 0.3 Torr. The interface nitridation reduces direct and Fowler–Nordheim tunneling by at least one order of magnitude, independent of film thickness. Incorporation of nitrogen at the top surface of the oxide in a concentration equivalent to about 1–2 molecular layers of silicon nitride in an “O–N” structure has been accomplished by N2/He remote plasma nitridation at 300 °C, but at a reduced process pressure of 0.1 Torr. Top surface nitridation has been shown to prevent boron diffusion out of p+ poly-Si gate electrodes during high-temperature activation anneals, e.g., at 1000 °C. Combining interfacial and top surface nitridation processes resulted in a “N–O–N” structure that was effective in reducing tunneling leakage currents and suppressing boron out-diffusion from p+ poly-Si gate electrodes. © 1999 American Vacuum Society.
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81.65.Mq Oxidation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Buried heterostructure complex-coupled distributed feedback 1.55 μm lasers fabricated using dry etching processes and quaternary layer overgrowth

D. Söderström, S. Lourdudoss, C.-F. Carlström, S. Anand, M. Kahn, and M. Kamp

J. Vac. Sci. Technol. B 17, 2622 (1999); http://dx.doi.org/10.1116/1.591035 (4 pages) | Cited 3 times

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An attractive process for fabricating buried heterostructure complex-coupled distributed feedback (BH-CC-DFB) lasers emitting at 1.55 μm has been developed. It combines low damage chemically assisted ion beam etching (CAIBE) for grating definition, subsequent overgrowth of a quaternary GaInAsP layer (λPL=1.22 μm) by low-pressure metalorganic vapor phase epitaxy, reactive ion etching for mesa definition and semi-insulating InP:Fe regrowth by hydride vapor phase epitaxy. CAIBE improves grating uniformity, GaInAsP layer overgrowth increases gain coupling and semi-insulating regrowth facilitates lateral mode confinement and thermal dissipation. The as-cleaved BH-CC-DFB lasers fabricated with the above combination show a statistical single mode yield of 87% and a very high side-mode suppression ratio up to 55 dB. A −3 dB bandwidth of 10 GHz is also demonstrated. © 1999 American Vacuum Society.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Control of wet-etching thickness in the vertical cavity surface emitting laser structure by in situ laser reflectometry

H. K. Cho, J. Y. Lee, B. Lee, J. H. Baek, and W. S. Han

J. Vac. Sci. Technol. B 17, 2626 (1999); http://dx.doi.org/10.1116/1.591036 (4 pages)

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We have investigated the use of in situ laser reflectometry for etch depth control in vertical cavity surface emitting laser (VCSEL) structures. We can obtain the precise etch depth by simply counting the number of oscillations during the wet-etching process. After calibration on an AlGaAs/GaAs 20-period distributed Bragg reflector (DBR) structure, this technique was applied to the monolithic 1.55 μm VCSEL device process that is required to etch epilayers of several μm thickness. In the 1.55 μm VCSEL structure, the mesa was generated by monitoring the number of peaks in the bottom DBR that corresponded to an etch depth of about 11 μm. The overall spatial uniformity of the etched sample was within a layer (1000 Å) by the distinction between layers. This process offers the possibility of precise control of etch depth for any multilayer structure. © 1999 American Vacuum Society.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.65.Cf Surface cleaning, etching, patterning
07.60.Hv Refractometers and reflectometers

Interferometry for end point prediction during plasma etching of various structures in complementary metal–oxide–semiconductor device fabrication

N. Layadi, S. J. Molloy, T. C. Esry, T. Lill, J. Trevor, M. N. Grimbergen, and J. Chinn

J. Vac. Sci. Technol. B 17, 2630 (1999); http://dx.doi.org/10.1116/1.591037 (8 pages) | Cited 2 times

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We present results of an interferometric end point prediction technique for use in plasma etching of various gate and localized oxidation of silicon (LOCOS) structures in advanced complementary metal–oxide–semiconductor device fabrication. Etch experiments were carried out in a production high-density plasma source (decoupled plasma source) reactor made by Applied Materials. The end point prediction technique has been applied successfully to many samples and types of structures commonly found in integrated circuit manufacturing. These include: doped and undoped polysilicon material; patterned and unpatterned wafers; flat and topographic surfaces; resist and hard-mask patterned wafers with oxide underlayers of various thicknesses; and product wafers with varied pattern density. The ability to predict endpoint and avoid breakthrough of gate oxides as thin as 19 Å has been investigated. The end point detection system has also been shown to be effective in other etch processes including LOCOS etch, where the end point of the Si3N4 etch on the underlying SiO2 must be triggered as early as possible to avoid excessive oxide loss or etching of the Si substrate. The flexibility of the end point algorithm together with the external trigger controller are demonstrated to be crucial for successful end point prediction. © 1999 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.30.De Semiconductor-device characterization, design, and modeling
07.60.Ly Interferometers

Abatement of perfluorocarbons with an inductively coupled plasma reactor

M. Y. Liao, K. Wong, J. P. McVittie, and K. C. Saraswat

J. Vac. Sci. Technol. B 17, 2638 (1999); http://dx.doi.org/10.1116/1.591038 (6 pages) | Cited 10 times

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Preliminary tests using an inductively coupled plasma (ICP) reactor to abate C2F6, CF4, and CHF3 show promising results. In conjunction with this, some of the operating parameters, which need to be considered when trying to obtain maximum abatement efficiency, are explored. Near 100% destruction efficiency (DRE) for the persistently fluorinated compounds (PFCs) mentioned earlier has been achieved with O2 as the additive gas. Similarly, the abatement of CF4 with CH4 and/or CH4/O2 as the additive gas, has shown comparable results. For the non-CF4 PFCs, like C2F6 and CHF3, the formation of CF4 as an abatement by-product was monitored and shown that it can be controlled by varying the operating parameters of the ICP reactor. The trends in the DRE observed while manipulating the ICP operating parameters such as ICP power, residence time, amount/type of additive gas, and Ar dilution, show that there are trade offs which must be taken into account. A quadrupole mass spectrometer was used for analyzing the abatement effluents. © 1999 American Vacuum Society.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Selective plasma etching for contact holes using a fluorine-based chemistry with addition of N2

Peter M. Meijer, Michel E. F. Roelofs, and Bart S. Manders

J. Vac. Sci. Technol. B 17, 2644 (1999); http://dx.doi.org/10.1116/1.591039 (4 pages) | Cited 1 time

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The effects the addition of nitrogen to a CHF3/CF4/Ar-gas mixture on the selectivity of SiO2 to TiSi2 and Si are reported for a magnetically enhanced reactive ion etch system. The selectivity to TiSi2 is more than doubled by adding 10% of nitrogen to the gas mixture, whereas the same addition lowers the selectivity to Si by more than half. The selectivity to TiSi2 is lowered by a factor of 2 by changing the wafer temperature from 70 to 100 °C. The selectivity to Si is not influenced by this change in wafer temperature. This contrasting behavior suggests different etch selectivity mechanisms for SiO2/TiSi2 and SiO2/Si. This is confirmed by x-ray photoemission spectroscopy measurements of the TiSi2 and Si surfaces. © 1999 American Vacuum Society.
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85.40.Ls Metallization, contacts, interconnects; device isolation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Sheath expansion in a drifting, nonuniform plasma

M. Keidar and I. G. Brown

J. Vac. Sci. Technol. B 17, 2648 (1999); http://dx.doi.org/10.1116/1.591040 (3 pages) | Cited 6 times

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A model is proposed for the sheath expansion into a nonuniform plasma with substantial drift velocity. We refer in particular to the streaming metal plasma produced by a vacuum arc discharge; this kind of plasma is characterized by its spatial nonuniformity and high ion drift velocity. It is shown that for a nonuniform plasma and high substrate bias voltage (>10 kV), the sheath thickness is significantly smaller than in a uniform plasma. High drift velocity also leads to a decrease in sheath thickness. For plasma immersion ion implantation carried out in a nonuniform plasma, the increase in ion implantation current with increasing voltage is different from that of a uniform plasma where the ion current is constant with voltage. This effect was found to be quantitative agreement with experiment. The decrease in sheath thickness with increasing plasma drift velocity can explain qualitatively the experimentally observed existence of a stable high-voltage sheath for a relatively long time. © 1999 American Vacuum Society.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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Anomalous scanning tunneling microscopy images of GaAs(110) surfaces due to tip-induced band bending

S. Aloni and G. Haase

J. Vac. Sci. Technol. B 17, 2651 (1999); http://dx.doi.org/10.1116/1.591041 (2 pages) | Cited 4 times

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Scanning tunneling microscopy (STM) images of clean nondegenerate GaAs(110) surfaces, which lack surface states in the band gap, often show the As sublattice at low positive sample bias (empty state image) for p-type material, or conversely, the Ga sublattice at low negative sample bias (filled state image) for n-type material. This happens because as the Fermi level of the tip is positioned inside the GaAs energy gap, no current can flow between the sample and the tip. As a result, the STM feedback brings the tip very close to the surface and the tip-induced electric field is greatly enhanced, creating a subsurface accumulation layer. © 1999 American Vacuum Society.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.20.At Surface states, band structure, electron density of states

Polycarbonate surface modified by argon cluster ion beams

J. Zemek, I. Yamada, G. Takaoka, and J. Matsuo

J. Vac. Sci. Technol. B 17, 2653 (1999); http://dx.doi.org/10.1116/1.591139 (3 pages) | Cited 3 times

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X-ray induced photoelectron spectroscopy and atomic force microscopy were used to gain detailed information on surface topography, composition and bonding among atoms in a near-surface region of untreated and modified polycarbonate surfaces by argon cluster and argon monomer ion irradiation. As a consequence of the cluster ion beam impingement on the polycarbonates, their surfaces become rough with polymer structure partially damaged. Surprisingly, the surface irradiated by argon monomer ions was found less rough but the polymer structure in a surface region completely lost its integrity and an amorphous (hydrogenated) carbon layer was formed. © 1999 American Vacuum Society.
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61.80.Jh Ion radiation effects
61.82.Pv Polymers, organic compounds
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Quantitative surface area evaluation of rugged polycrystalline Si plate for dynamic random access memory capacitor by xenon adsorption

Hiroshi Yanazawa, Takuya Futase, and Isao Suzuki

J. Vac. Sci. Technol. B 17, 2656 (1999); http://dx.doi.org/10.1116/1.591042 (4 pages) | Cited 1 time

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The idea of rugged polycrystalline Si plate to increase dynamic random access memory capacitor is now going to be realized in mass production. Effective surface areas of polycrystalline Si films were evaluated by measuring xenon adsorption before and after surface roughened process. The surface area was increased by 1.8 times due to roughened process. This result is consistent with the value of 2.1 obtained from capacitance measurements on the samples prepared under the same condition. This work shows the applicability of ultrahigh sensitive gas adsorption to thin film surface characterization. Gas adsorption gives a new quantitative measure for analyzing surface morphology in addition to the qualitative observations by scanning electron microscopy and atomic force microscopy. © 1999 American Vacuum Society.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)

Trimethylamine: Novel source for low damage reactive ion beam etching of InP

C. F. Carlström, S. Anand, and G. Landgren

J. Vac. Sci. Technol. B 17, 2660 (1999); http://dx.doi.org/10.1116/1.591043 (4 pages) | Cited 1 time

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A new reactive ion beam etching process using trimethylamine for low damage etching of InP at room temperature has been developed. Characteristics of the etching process, i.e., etch rate, surface morphology, and etch-induced damage are reported. Photoluminescence yield (PLY) was used to characterize the residual damage by using near-surface quantum wells as probes and the etched surface morphologies were quantified by roughness measurements using atomic force microscopy. The etch rate could be varied by over an order of magnitude, from low (∼4nm/min) at 75 eV up to 100 nm/min at 500 eV. The etched surfaces were extremely smooth (rms roughness <1nm) independent of ion energy. This was so even for samples etched to a depth of more than 1 μm. Process induced damage as measured by PLY was also significantly smaller than for CH4 based dry etch processes. Further, upon annealing at 650 °C in a PH3 ambient, the etched samples showed near complete PLY recovery, indicating significant damage reduction. Hence, the new process results in a simplified plasma chemistry that provides not only reasonable etch rates but also extremely smooth surfaces and low optical damage. © 1999 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)

Destructive abatement of CF4 and C2F6 via a plasma induced reaction with CaO

James L. Delattre, Todd L. Friedman, and Angelica M. Stacy

J. Vac. Sci. Technol. B 17, 2664 (1999); http://dx.doi.org/10.1116/1.591044 (3 pages) | Cited 4 times

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The plasma induced reactions of CF4 and C2F6 with CaO powder were examined in an effort to develop new methodologies for perfluorocarbon abatement. The reaction of CaO with CF4 (10 sccm flow), activated by an inductively coupled plasma (500 W and 100 mTorr) resulted in the destruction of >70% of the CF4. Under the same conditions >80% of C2F6 was destroyed. For both reactions, the major solid product is polycrystalline CaF2, an environmentally benign mineral with commercial value. The major gaseous products are CO and CO2. These reaction products are attractive alternatives to fluorine-containing byproducts such as F2(g), COF2(g), and HF(aq) generated by traditional perfluorocarbon abatement techniques. © 1999 American Vacuum Society.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Formation of low resistance Pt ohmic contacts to p-type GaN using two-step surface treatment

Ja-Soon Jang, Seong-Ju Park, and Tae-Yeon Seong

J. Vac. Sci. Technol. B 17, 2667 (1999); http://dx.doi.org/10.1116/1.591045 (4 pages) | Cited 63 times

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Two-step surface treatment is introduced to obtain low resistance Pt contacts to p-type GaN. The first step is performed after the mesa etching process using buffered oxide etch (BOE) and ammonium sulfide [(NH4)2Sx]. This is followed by the second step using BOE. The Pt contact, that was simply BOE treated, yields 2.1(±0.9)×10−2 Ω cm2. However, the contact which was treated sequentially using ultrasonically boiled BOE (10 min) and boiled (NH4)2Sx (10 min), produces a specific contact resistance of 2.0(±3.5)×10−5 Ω cm2. To the best of our knowledge, this is the lowest contact resistance reported hitherto for the contacts on p-GaN. The effective Schottky barrier heights (SBHs) of the differently surface-treated contacts were determined using the Norde and current–voltage methods. It is shown that the SBHs are dependent upon the surface treatment conditions. © 1999 American Vacuum Society.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
73.40.Cg Contact resistance, contact potential

Fabrication of submicrometer regular arrays of pillars and helices

M. Malac, R. F. Egerton, M. J. Brett, and B. Dick

J. Vac. Sci. Technol. B 17, 2671 (1999); http://dx.doi.org/10.1116/1.591046 (4 pages) | Cited 45 times

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We use a glancing-angle deposition technique to produce regular lattices of submicrometer pillars and helices with a two-dimensional lattice constant below 1 μm and structure heights of 0.5–10 μm. Possible applications of such structures include photonic crystals and magnetic-storage media. © 1999 American Vacuum Society.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.70.Qs Photonic bandgap materials

Effect of Au overlayer on Ni contacts to p-type GaN

Jong Kyu Kim, Jong-Lam Lee, Jae Won Lee, Yong Jo Park, and Taeil Kim

J. Vac. Sci. Technol. B 17, 2675 (1999); http://dx.doi.org/10.1116/1.591135 (4 pages) | Cited 7 times

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The effect of Au overlayer on Ni contacts to p-type GaN was investigated by comparing the change of electrical properties with interfacial reactions at the interface of Ni/p-type GaN. The contact resistivity at the interface of Ni/p-type GaN was decreased by two orders of magnitude at 600 °C by incorporating the Au overlayer on the Ni contact. This originates from the outdiffusion of Ga atoms from p-type GaN to the Au overlayer, and subsequently produces Ga vacancies acting as acceptors for electrons below the contact. Consequently, net hole concentration increases below the contacts, resulting in the reduction of the Schottky barrier height for hole transport, via the decrease of contact resistivity. © 1999 American Vacuum Society.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
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back to top ALIGNMENT, METROLOGY, AND TESTING

Sub-100 nm metrology using interferometrically produced fiducials

M. L. Schattenburg, C. Chen, P. N. Everett, J. Ferrera, P. Konkola, and Henry I. Smith

J. Vac. Sci. Technol. B 17, 2692 (1999); http://dx.doi.org/10.1116/1.591047 (6 pages) | Cited 28 times

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Pattern-placement metrology plays a critical role in nanofabrication. Not far in the future, metrology standards approaching 0.2 nm in accuracy will be required to facilitate the production of 25 nm semiconductor devices. They will also be needed to support the manufacturing of high-density wavelength-division-multiplexed integrated optoelectronic devices. We are developing a new approach to metrology in the sub-100 nm domain that is based on using phase-coherent fiducial gratings and grids patterned by interference lithography. This approach is complementary to the traditional mark-detection, or “market plot” pattern-placement metrology. In this article we explore the limitations of laser-interferometer-based mark-detection metrology, and contrast this with ways that fiducial grids could be used to solve a variety of metrology problems. These include measuring process-induced distortions in substrates; measuring patterning distortions in pattern-mastering systems, such as laser and e-beam writers; and measuring field distortions and alignment errors in steppers and scanners. We describe a proposed standard for pattern-placement metrology, which includes both a fiducial grid and market-type marks. Finally, a number of methods through which phase-coherent periodic structures can be patterned are shown, including “traditional” interference lithography, achromatic interference lithography, near-field interference lithography, and scanning-beam interference lithography. © 1999 American Vacuum Society.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
06.20.F- Units and standards

Novel mask-wafer gap measurement scheme with nanometer-level detectivity

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

J. Vac. Sci. Technol. B 17, 2698 (1999); http://dx.doi.org/10.1116/1.591048 (5 pages) | Cited 9 times

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We describe a means of measuring the gap between mask and substrate in an x-ray lithography system. The method does not require that the gap be scanned. The method encodes the gap in the spatial phase, spatial frequency, and separation of sets of interference fringes. The fringes result from the diffraction from a checkerboard on the mask, with constant period in one direction and varying period in the transverse direction. The separation of fringe sets gives an unambiguous measure of gap when the mask is approaching the substrate, from 400 to 30 μm. At the smaller gaps used for exposure, checkerboards with different chirp periods are utilized to indicate the gap without ambiguity. The phases of the fringes as a function of gap were calibrated with a Fabry-Pérot interferometer. The repeatability of the phases between consecutive scans of gap was found to have a 5 nm standard deviation. This method of measuring gap may prove useful in a variety of applications that require a controlled gap between two plates. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers

A holographic phase-shifting interferometer technique to measure in-plane distortion

Michael H. Lim, Juan Ferrera, K. P. Pipe, and Henry I. Smith

J. Vac. Sci. Technol. B 17, 2703 (1999); http://dx.doi.org/10.1116/1.591049 (4 pages) | Cited 4 times

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We describe the use of holographic phase-shifting interferometry (HPSI) to measure in-plane distortion of a substrate in which a shallow grating, produced by interferometric lithography, has been etched. The diffractive metrology inherent in HPSI should enable one to study process-induced distortions down to the level of a few nanometers. We used HPSI to investigate distortion introduced by the anodic bonding of silicon nitride membranes to Pyrex frames in x-ray lithography masks. This was part of an effort to develop an inverted x-ray mask configuration. The HPSI technique gave quantitative measurements of the linear and nonlinear components of distortions in one-dimension. The high levels of distortion found were presumably introduced by the high temperatures used in anodic bonding, combined with the asymmetric manner in which the membranes were brought into contact with the Pyrex frame. The comprehensive, quantitative measurement of distortion provided by HPSI should enable us to modify the mask making process so as to avoid steps that introduce distortion. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
42.40.Kw Holographic interferometry; other holographic techniques

High-throughput, high-spatial-frequency measurement of critical dimension variations using memory circuits as electrical test structures

X. Ouyang, Timothy L. Deeter, C. N. Berglund, Mark A. McCord, and R. F. W. Pease

J. Vac. Sci. Technol. B 17, 2707 (1999); http://dx.doi.org/10.1116/1.591050 (7 pages) | Cited 1 time

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Critical dimension (CD) errors are traditionally specified and characterized without reference to their spatial frequency spectra. However, a given amplitude of CD variation can have very different consequences depending on its spectrum. CD errors whose variation is over a few micrometers can be much more serious than those of the same magnitude that extend over several chips. Existing CD metrology tools, such as scanning electron microscopy or electrical resistance measurements, are seldom used to characterize these short-range CD variations, particularly those with spatial wavelengths below 100 μm, because of the large amount of data required and the difficulty of collecting data in such a dense grid. We report a new method of measuring CD variations using static random-access memory (SRAM) circuits in which direct measurements of bit-line currents reveal the individual transistor gate length variations within each memory cell. With the compactness and regularity of the SRAM layout we can measure CD variations with spatial periodicities down to 6 μm. By repeatedly measuring each cell in a memory chip and recording the corresponding currents we can achieve sufficient data to minimize noise, and through two-dimensional bandpass filtering 0.2 nm CD variations can be detected. Two designs of 4 Mbit SRAMs fabricated using 250 nm design rules were studied. The resulting CD variations yielded spectra that were dominated by peaks whose origins included uncorrected electron beam and optical proximity effects. Pattern-independent variations ascribable to the reticle generator itself appeared to contribute only a small fraction of the total error observed. © 1999 American Vacuum Society.  
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
84.30.Sk Pulse and digital circuits

Thin film stress mapping using an integrated sensor

M. P. Schlax, A. F. Jachim, R. L. Engelstad, E. G. Lovell, J. A. Liddle, and A. E. Novembre

J. Vac. Sci. Technol. B 17, 2714 (1999); http://dx.doi.org/10.1116/1.591051 (5 pages) | Cited 3 times

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The integrated sensor complementary electrode (ISCE) stress mapping tool has been created for process development and characterization of blank SCALPEL masks (4-in. format). The SCALPEL mask design incorporates a 0.1-μm-thick SiN membrane with a Cr/W scattering bilayer supported by a grillage of Si struts. The ISCE was used to determine the resonant frequency and consequently the stress of each freestanding window (or membrane) created by the grillage. Discrete stress values for each window were combined to develop a stress contour map across the complete mask membrane area. The ISCE tool utilizes 120 sensor pads integrated into and multiplexed on a two-sided computer numerically controlled (CNC) milled circuit board. The gap between the sensor board and the mask is fixed so there are no moving parts. Advantages to this design are increased speed and reduced cost and size. Stress mappings for two 4-in. SCALPEL masks were completed using the integrated sensor board and results are shown. The worst case repeatability of window resonant frequency was 1.0%. A detailed uncertainty analysis of the stress mapping results is presented. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Mechanical characterization of electron-beam resist using micromachined structures

L. Que, Y. B. Gianchandani, and F. Cerrina

J. Vac. Sci. Technol. B 17, 2719 (1999); http://dx.doi.org/10.1116/1.591052 (4 pages) | Cited 3 times

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In this effort the residual strain in exposed negative tone SAL 605 and unexposed positive tone APEX-E resists was characterized for a variety of processing conditions using surface micromachined bent-beam strain sensors fabricated with resist as the structural material. Results showed that SAL 605 is in 1035–1230 μstrain compression, whereas APEX-E is in 653–690 μstrain tension for the conditions tested. Residual stress in APEX-E was also determined by wafer curvature measurements. The ratio of the residual stress to strain at room temperature indicated that the Young’s modulus of this material is 21±5 GPa. The temperature dependence of the stress indicated that the glass transition temperature for APEX-E is 118±2 °C, and its coefficient of thermal expansion is 11.0±2.5 ppm/K. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)
07.10.Cm Micromechanical devices and systems
62.20.D- Elasticity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
65.40.De Thermal expansion; thermomechanical effects
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Pz Instruments for strain, force, and torque

Correlation of atomic force microscopy sidewall roughness measurements with scanning electron microscopy line-edge roughness measurements on chemically amplified resists exposed by x-ray lithography

Geoffrey W. Reynolds and James W. Taylor

J. Vac. Sci. Technol. B 17, 2723 (1999); http://dx.doi.org/10.1116/1.591053 (7 pages) | Cited 14 times

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As critical dimensions of resist features shrink, roughness of the features may contribute significantly to the variation in critical dimension. Measuring and understanding the causes of this roughness will become increasingly important with smaller sizes. To date, mainly two techniques have been used to measure the roughness: atomic force microscopy (AFM) and scanning electron microscopy (SEM). Topdown SEM measurements provide an easy and expedient measure of the variation in the profile of the resist feature. These measurements are often called “line-edge roughness” (LER). AFM measurements are considerably more time consuming, but provide information on the entire sidewall surface of the resist, rather than just the profile in line-edge roughness. Our recent AFM measurements on the positive-tone resist APEX-E and UV5 have shown that the sidewall roughness of the resist is depth dependent; resist near the substrate is smoother than resist at the top surface of the resist. For instance, APEX-E may have a roughness on the order of 3 nm rms near the substrate, which may increase to 7 or so nm rms at the top of the resist line. This article will correlate measurements made by both AFM and SEM and explore how the depth-dependent roughness in AFM data may affect the magnitude of the roughness measured by topdown SEM. © 1999 American Vacuum Society.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
85.40.Hp Lithography, masks and pattern transfer
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.79.Lh Atomic force microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Control of localized access to circuitry through the backside using focused ion beam technology

Nicholas Antoniou, Mark Thompson, Jesse Salen, David Casey, Rama R. Goruganthu, Rose Ring, Jeff Birdsley, and Glen Gilfeather

J. Vac. Sci. Technol. B 17, 2730 (1999); http://dx.doi.org/10.1116/1.590926 (4 pages) | Cited 1 time

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Complex logic chips are almost exclusively assembled in flip chip packaging. This type of assembly complicates traditional debug and circuit modification techniques. Development of new applications and new equipment now enable precise access to the circuitry of flip chip parts. One such application and the equipment developed are being introduced in this article. The technique makes use of optical beam induced current (OBIC) as a way to measure the amount of silicon that is left covering active areas of a flip chip circuit after a trench has been milled in the bulk silicon using a focused ion beam (FIB) system. The apparatus is all contained in one system thus enhancing the throughput of such work. When accessing the circuitry of flip chip parts, it is crucial to be able to locally remove silicon from the backside to within a few microns of the circuitry. This is necessary in order to preserve the integrity of the part and allow access to the circuitry for probe point creation or circuit modification using FIB. OBIC offers a high level of resolution and accuracy in measuring thin layers of bulk silicon in flip chips. In this article we describe the apparatus used, the details of the application, data collected, and a theoretical model developed to confirm the experimental findings. © 1999 American Vacuum Society.
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85.40.Hp Lithography, masks and pattern transfer
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Fabrication of two-dimensional photonic crystal waveguides for 1.5 μm in silicon by deep anisotropic dry etching

T. Zijlstra, E. van der Drift, M. J. A. de Dood, E. Snoeks, and A. Polman

J. Vac. Sci. Technol. B 17, 2734 (1999); http://dx.doi.org/10.1116/1.591054 (6 pages) | Cited 48 times

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Fabrication process for sharp waveguide bends in a two-dimensional photonic band gap structure in silicon is developed. The waveguide bend is defined by removing a row of pillars in a two-dimensional photonic crystal of 5 μm long, 205 nm diameter pillars placed on a square lattice with a pitch of 570 nm. To meet the severe nanotolerance requirements in such a device the SF6/O2 electron cyclotron resonance plasma process at reduced temperature is tailored to extreme profile control. The impact of main plasma parameters—i.e., temperature, oxygen/fluorine content, and ion energy—on the sidewall passivation process is unraveled in detail. Crystallographic orientation preference in the etch rate is observed. © 1999 American Vacuum Society.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

High-aspect-ratio nanophotonic components fabricated by Cl2 reactive ion beam etching

W. J. Zubrzycki, G. A. Vawter, and J. R. Wendt

J. Vac. Sci. Technol. B 17, 2740 (1999); http://dx.doi.org/10.1116/1.591055 (5 pages) | Cited 3 times

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We describe highly anisotropic reactive ion beam etching of nanophotonic structures in AlGaAs based on the ion beam divergence angle and chamber pressure. The divergence angle is shown to influence the shape of the upper portion of the etch while the chamber pressure controls the shape of the lower portion. Deeply etched distributed Bragg reflectors are etched to an aspect ratio of 8:1 with 100 nm trench widths. The profile of the grating etch is straight with smooth sidewalls, flat bottoms, and squared corners. Two-dimensional photonic crystal post arrays are fabricated with smooth and vertical sidewalls, with structures as small as 180 nm in diameter and 2.0 μm in height. © 1999 American Vacuum Society.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning
42.70.Qs Photonic bandgap materials
42.79.Dj Gratings

Cl2 plasma passivation of etch induced damage in GaAs and InGaAs with an inductively coupled plasma source

E. W. Berg and S. W. Pang

J. Vac. Sci. Technol. B 17, 2745 (1999); http://dx.doi.org/10.1116/1.591056 (5 pages) | Cited 4 times

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Low energy Cl species generated in an inductively coupled plasma source have been used to passivate etch induced damage in GaAs and InGaAs. Improved electrical and optical characteristics were measured after Cl2 plasma passivation. The ideality factor and barrier height of etched GaAs Schottky diodes were improved back to the values of an unetched sample with a 10 min passivation. No etching occurred during passivation due to the presence of a surface oxide layer. The growth conditions of the oxide layer were found to have a large effect on the ability of the Cl2 plasma to passivate the surface. It was found that native oxides allow more effective passivation by Cl species as compared to plasma grown oxides. The passivation techniques were used to passivate damage along an etched sidewall for improved electrical conductivity of GaAs wires and increased photoluminescence signal from etched gratings containing an InGaAs quantum well. © 1999 American Vacuum Society.
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81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.30.Kk Junction diodes

Inductively coupled plasma reactive ion etching of AlxGa1−xN for application in laser facet formation

F. A. Khan, L. Zhou, A. T. Ping, and I. Adesida

J. Vac. Sci. Technol. B 17, 2750 (1999); http://dx.doi.org/10.1116/1.591057 (5 pages) | Cited 11 times

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The etching characteristics of AlxGa1−xN grown by metal–organic chemical-vapor deposition were investigated in an inductively coupled plasma (ICP) reactive ion etching system using Cl2/Ar gas mixtures. Etch rate variations with substrate bias voltage, ICP coil power, chamber pressure, Cl2/Ar gas mixture ratios, and gas flow rates were investigated. The optimum chamber pressure for etching was found to be dependent on both the substrate bias voltage and ICP coil power. Auger electron spectroscopy analysis showed that the stoichiometries of the etched Al0.22Ga0.78N surfaces were identical, independent of the etching conditions. Etching results were successfully applied to form highly anisotropic and smooth facets in GaN/InGaN/AlGaN heterostructure laser materials. © 1999 American Vacuum Society.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Dv Composition, segregation; defects and impurities
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)