bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of reactively sputtered WNx film as a gate metal for self-alignment GaAs metal–semiconductor field effect transistors
Authors: Uchitomi N. , Nagaoka M. , Shimada K. , Mizoguchi T. , Toyoda N.
Published: July 2002

Properties of reactively sputtered WNx films on a GaAs substrate have been investigated by electrical and physical analyses. WNx films were deposited from a pure W target by using three types of sputtering systems: (1) Magnetron sputtering system equipped with rf and dc mode; (2) S-gun sputtering system; (3) rf diode sputtering system. The composition of WNx films was easily and reproducibly controlled by changing the N2 content in Ar–N2 mixed ambient gas. The WNx–GaAs system was both electrically and metallurgically stable even after high-temperature annealing of up to 800 °C. The Schottky barrier height to n-type GaAs was more than 0.8 V, which is the highest value obtained so far among any other refractory metals. Self-aligned GaAs MESFET’s were successfully fabricated using a WNx gate. The transconductance was typically 150 mS/mm for 1.5 μm gate length.
Si surface study after Ar ion-assisted Cl2 etching
Authors: Takasaki Nahomi Aoto , Ikawa Eiji , Kurogi Yukinori
Published: July 2002

Silicon surfaces after Ar ion-assisted etching in Cl2 gas atmosphere were studied for various Ar ion current densities and Cl2 gas pressures. The number of incident Ar ions was varied in 6×1014–3×1016 ions/cm2/s while the number of incident Cl2 molecules was varied in 0–3×1017 molecules/cm2/s. Ar ion acceleration energy was fixed at 1 keV. High etching rate, about 5000 Å/min, was observed with a high incident rate of both Ar ions and Cl2 molecules. On the other hand, high etch yield was observed at low incident rate of Ar ions and high incident rate of Cl2 molecules. The amount of surface defects and surface chemical adsorption states, which vary with different etching conditions, were studied by etch pit observation after thermal oxidation followed by Secco-etching, x-ray photoelectron spectroscopy (XPS), and reflection high energy electron diffraction (RHEED). Silicon surfaces, etched under high etch yield etching conditions, showed relatively high Si2O3 existence by XPS measurement, and high density etch pits. It is considered to be related with high density surface defects and roughness. Etch pits did not appear after conventional wet cleaning process. It is caused by a little surface oxidation and relatively less Si2O3 existence than other kinds of oxides on the surface.
Fermi level pinning and chemical interactions at metal–InxGa1−xAs(100) interfaces
Authors: Brillson L. J. , Slade M. L. , Viturro R. E. , Kelly M. K. , Tache N. , Margaritondo G. , Woodall J. M. , Kirchner P. D. , Pettit G. D. , Wright S. L.
Published: July 2002

Soft x-ray photoemission spectroscopy (SXPS) measurements of metals on clean, ordered InxGa1−xAs(100) surfaces reveal that Fermi level stabilization energies depend strongly on the particular metal, i.e., the Fermi level is not pinned. For InxGa1−xAs, x>0, the range of Fermi level movement is comparable to or greater than the semiconductor band gap. For the same metal on different alloys, we observe regular trends in stabilization energies. The trend for Au is strikingly different from previous, air-exposed values. Our results challenge Schottky barrier models based on simple native defects, metal-induced gap states, or the ‘‘common-anion’’ rule. Observed variations in semiconductor outdiffusion provide a chemically-modified interface work function model which accounts for the data across the alloy series.
Surface diffusion measured by laser-induced desorption: Monte Carlo simulation of effects of surface defects on diffusion
Authors: Hall Richard B. , Upton Thomas H. , Herbolzheimer Eric
Published: July 2002

Recently, pulsed laser-induced desorption (LID) has been used to measure surface diffusion of adsorbed species. Often, however, pulsed-laser excitation leads to stress-induced deformations of the surface. We have found, in the case of a Ni(100) surface, that laser excitation causes a change in the surface morphology that results in an increase in the dissociative sticking coefficient of hydrogen by a factor of more than 3. At the same time, adsorption of other species is not appreciably affected. Based on low-energy electron diffraction (LEED) spot profile analysis, the laser-irradiated surface has <10% atomic-step defects. We attempt to estimate the effect that laser-induced surface defects have on the measurement of diffusion by means of a Monte Carlo simulation. Surface defects are introduced into the simulation as trap sites because such defects would have the most pronounced effect on diffusion. We find that 〈x(t)〉 and 〈x2(t)〉 of particles on the defected surface are characteristic of diffusion and obtain an effective diffusion coefficient D from the rate of increase in 〈x2〉 with time. For a p(2×2) array of trap sites and noninteracting particles, D decreases with increasing trap site residence time but the magnitude of the decrease is not large. For example, D is decreased only by a factor of roughly 3 when the trap residence time is 3000 times the normal site residence time. The number of particles N(t) that migrate onto the defected portion of the surface under these conditions is reduced by <10% relative to a defect-free surface. These variations are within the present experimental uncertainties of the LID technique. Hence, for noninteracting adsorbates such as hydrogen, the reported values of D are representative of the defect-free surface. Using the result that diffusion on the defected portion of the surface can be represented by a single effective diffusion coefficient, we derive an analytic expression for the effects of trap sites on N(t). This analytic expression accurately reproduces the Monte Carlo results.
Optical printability of defects in two-dimensional patterns
Authors: Huynh Bachvan , Toh K. K. H. , Haller W. E. , Neureuther A. R.
Published: July 2002

Experiments, simulation, and algebraic analysis are used to characterize the printability of defects in various classes of features in optical projection printing. A special test mask was designed with programmed defects located adjacent to isolated lines, arrays of lines, corners, elbows, and nested elbows. These patterns were then projection printed in an exposure–focus matrix in a positive resist process on various substrates and examined in detail via scanning electron micrographs. For small defects of both polarities, the linewidth variation on isolated lines is shown to be K* (defect area) where K is 1 and 2.4 for transparent and opaque defects, respectively. For equal line and space arrays of minimum-sized features [0.8* λ/numerical aperture (NA)], opaque defects as small as 0.3* λ/NA cause bridging while transparent defects as large as 0.5* λ/NA do not cause opens. Elbows and nested elbows are slightly more sensitive than arrays of lines due to intrafeature proximity effects. The interior corners are also sensitive to defects. Underexposure greatly increases the effects of opaque defects while defocus has little impact. The effects on aluminum substrates show similar trends to those on silicon while for thin resist on silicon, even much smaller defects print. The printability of transparent defects in positive resist is easy to model and a constant intensity threshold model is generally adequate. For opaque defects, nonvertical resist development effects typically occur and must be included in the simulation.
A variable energy focused ion beam system for i
n s
i
t
u microfabrication
Authors: Narum D. H. , Pease R. F. W.
Published: July 2002

The combination of molecular-beam epitaxy with focused ion beam (FIB) technology offers the opportunity for generating true three-dimensional ultrasubmicron structures. One problem, however, is that conventional FIB systems employ landing energies of ∼50 keV and up, and so the spatial extent of damage by the beam, exceeds both the radius of the beam and the thickness of layers frequently grown. We have investigated focusing of beams of ions of energies down to 25 eV by employing retarding field optics. Modeling of the optics indicates that space charge becomes serious at currents above 1 nA for Ga+ ions of 50-eV energy but that submicron beams of such ions are possible at lower currents. An experimental column was built and largely confirmed the predictions. Beam diameters were measured to be within a factor of 2 of the predicted value with a value of 0.95 μm for a 1-nA beam of Ga+ ions of landing energy of 25 eV.
Thermal and photostimulated reactions on Si2H6-adsorbed Si(100)2×1 surfaces: Mechanisms of Si film growth by atomic-layer epitaxy
Authors: Suda Y. , Lubben D. , Motooka T. , Greene J. E.
Published: July 2002

Electron energy-loss spectroscopy (EELS) and reflection high-energy electron diffraction (RHEED) have been used to investigate thermal and photothermal reactions in dihydride (1×1)::2H surfaces obtained by dosing clean Si(100)2×1 surfaces to a saturation exposure (≊2×1017 cm−2) of Si2H6 at 300 K. With 15-s anneals at progressively higher temperatures, the (1×1)::2H was transformed to a (2×1):H monohydride phase at temperatures between 655 and 725 K and most of the remaining H evolved by 765 K. Complete recovery of the initial clean-surface EELS spectrum and 2×1 RHEED pattern, signaling deposition of one layer of epitaxial Si(100)2×1, was obtained between 845 and 955 K. One pulse of 120 mJ cm−2 ArF laser-beam irradiation resulted in significant hydrogen evolution from Si2H6-saturated dihydride surfaces at 300 K and complete hydrogen desorption, with the reestablishment of the initial clean-surface EELS spectrum, at 525 K. The mechanism was found to be photothermal rather than photolytic and the maximum temperature during the ≊20-ns pulse (at 525-K starting temperature) was calculated to be 800 K. RHEED patterns from dihydride surfaces irradiated at 525 K were 2×1, but with slightly weakened half-order diffraction spot intensities. In initial film growth experiments using continuous Si2H6 dosing and pulsed ArF laser irradiation, epitaxial Si was obtained at a steady-state temperature of 525 K.
The National Institute of Standards and Technology molecular measuring machine project: Metrology and precision engineering design
Authors: Teague E. Clayton
Published: July 2002

At NIST, a high risk project has been undertaken to build an ultrahigh accuracy planar coordinate measuring machine capable of positioning and measuring to atomic scale accuracies over an area of 2500 mm2 . The design goal is to obtain a point-to-point spatial resolution of 0.1 nm of the distance between any two points within a 50 mm×50 mm×100 μm volume; with a net uncertainty for point-to-point measurements of 1.0 nm. Maximum specimen size will be 50 mm×50 mm×12 mm3. The approach has been to design the machine such that it can incorporate a probe, based on either a scanning tunneling microscope or an atomic force microscope, into a highly stable core mechanical structure. A spherical core structure, with crossed linear slideways for the probe and specimen carriages, was chosen for its high mechanical stiffness and ease of temperature control. Presented in this paper are: a summary of the precision instrument design fundamentals incorporated into our design; details of the overall mechanical design, X-Y drive systems, the metrology reference system, X-Y heterodyne interferometer, vibration isolation systems; and a report on the status of construction.
High-performance GaAs/AlGaAs graded refractive index separate confinement heterostructure lasers grown by molecular-beam epitaxy on Si3N4 masked substrates
Authors: Van Gieson E. , Meier H. P. , Harder C. , Buchmann P. , Webb D. , Walter W.
Published: July 2002

High-performance single quantum well graded refractive index separate confinement heterostructure lasers have been grown by molecular-beam epitaxy on Si3 N4 masked substrates. Lateral optical, carrier, and current confinement is supplied by the faceting which occurs during growth. Stripe lasers fabricated on 10-μm-wide openings in the [011̄] direction have threshold currents as low as 15 mA and internal quantum efficiency of 81% for a 500-μm-long cavity.
Photovoltaic effects in photoemission studies of Schottky barrier formation
Authors: Hecht M. H.
Published: July 2002

It is shown here that much of the recent photoelectron spectroscopy literature describing the onset of pinning in adsorbate–semiconductor systems at low temperature must be reinterpreted in light of surface photovoltaic effects. Two sources of surface charging are discussed, both of which are strongly enhanced at low temperature. The surface photovoltage resulting from separation of electron–hole pairs by the electric field in the depletion region is usually the dominant source of surface potential shifts, and causes flattening of the semiconductor bands. In addition, surface charging due to photoemission into the vacuum may reverse bias a p-type diode at low temperatures, causing increased band bending.
Electrostatic and contact forces in force microscopy
Authors: Hao Huang Wen , Baró A. M. , Sáenz J. J.
Published: July 2002

We have been measuring the electrostatic and contact forces between a tip and a graphite surface in a force microscope, which uses a polarizing optical interferometer. For large distances where the electrostatic force predominates, the data are analyzed in terms of a model which introduces the elongated shape of an actual tip. We find that the macroscopic tip has to be taken into account when analyzing the experimental data. The model allows us to deduce the effective radius of the tip which is operative in the electrostatic interaction. We also analyze the contact problem. The attractive part is consistent with van der Waals (vdW) forces. The repulsive regime shows an anomalously small level deflection which is attributed to the deformation of the sample surface. The adhesion of the tip sample is also measured.
Sub-quarter-micron gate pattern fabrication using a transparent phase shifting mask
Authors: Watanabe Hisashi , Takenaka Hiroshi , Todokoro Yoshihiro , Inoue Morio
Published: July 2002

Phase shifting technologies with an i-line stepper are applied for the application of defining sub-quarter-micron gate patterns for GaAs field-effect transistor (FET) devices. Transparent-type phase-shifting masks which have no chromium layer for printing the patterns are used. Using the phase-shifting technologies for gate delineation, it is shown that fine gate patterns with large pad areas can be defined. We have fabricated gate patterns for high-performance GaAs FET devices with gate lengths in the 0.15–0.5 μm range.
Registration of soft x radiation in As2S3 layers
Authors: Spassova E. , Danev G. , Guttmann P.
Published: July 2002

The photographic behavior of unsensitized evaporated layers of As2S3 exposed by x rays in the spectral region of 2–7 nm is studied. The photographic sensitivity is found to be 500–600 mJ/cm2 and the limits of photographic treatment are determined. It is concluded that the layers could be discussed as promising material for x-ray microlithography.
Comparison of various low-temperature scanning tunneling microscopy designs for use in spectroscopy and topography
Authors: Adler J. G. , Chen T. T. , Gallagher M. C. , Konkin M. K. , Mullin D. P.
Published: July 2002

We report on experiences operating over a dozen scanning tunneling microscopes in liquid helium at 4.2 K over the past four years. The microscopes were both bimorph and tube scanner designs. Most of our scanning tunneling microscopes (STMs) had ceramic frames, but as some of the early models survived only a limited number of thermal cycles (between room temperature and helium temperatures) we also constructed some with metal frames, using titanium. The calibration of the piezoelectric translators at 4.2 K as well as adjustment for the nonorthogonality of the scan directions are discussed. We also discuss various ways we have found satisfactory for the fine approach (tip to sample) in liquid helium. Data obtained with various microscopes are shown.
Operational characteristics of SF6 etching in an electron cyclotron resonance plasma reactor
Authors: Cecchi J. L. , Stevens J. E. , Jarecki R. L. , Huang Y. C.
Published: July 2002

The initial operation of an electron cyclotron resonance (ECR) plasma etch tool, utilized in a downstream configuration for SF6 etching of polysilicon is described. Practical operational characteristics that are generic to high-density, wave-supported plasma sources operated in downstream configurations were explored. A method for improved coupling of the microwave power to the ECR source is described. This method eliminates the need for external tuning. The effect of wall impurities on the plasma and etching characteristics is also considered. A scheme for conditioning the walls to alleviate the effects of impurities is presented. Finally, the complicated relationship between the ECR source plasma and the downstream wafer is considered, by examining the scaling of the plasma electron density in the two regions with microwave power and gas pressure. The phenomena discussed here apply to other etching chemistries and can have a significant impact on process integrity and ease of operation.
Ion-induced deposition for x-ray mask repair: Rate optimization using a time-dependent model
Authors: Petzold H.-C. , Heard P. J.
Published: July 2002

Focused ion beam (FIB) induced tungsten deposition is a very promising candidate for the repair of clear x-ray mask defects. However, it requires careful process control due to the sputtering which accompanies deposition. To improve our understanding of the process and to optimize its parameters in view of high-throughput mask repair, we developed a model of FIB induced deposition. It is based on a model reported previously, but additionally includes two parameters of outstanding importance for the process: the FIB’s dwell time and its loop time. The model was tested by applying it to the results of deposition experiments in which the influence of various parameters on the growth rate was investigated. Based on that comparison between experiment and theory, we make a prediction on the achievable repair speed as a function of the defect size. In our experiments, we obtained deposition rates of up to 20 nm/s. The x-ray opacity of the deposited layers is in the order of 80% of the tungsten bulk value.
Structure of the Bi/InP(110) interface: A photoemission extended x-ray absorption fine-structure study
Authors: Choudhary K. M. , Mangat P. S. , Seshadri P. , Kilday D. , Margaritondo G.
Published: July 2002

We studied the Bi/InP(110) interface for 0.35- and 0.9-monolayer (ML) Bi coverages by photoemission extended x-ray absorption fine-structure (PEXAFS). P 2p PEXAFS data were acquired. The data were analyzed by Fourier filtering followed by phase analysis using a novel curve-fitting procedure in which the E0 is also floated. For 0.9-ML Bi/InP(110), the results show that Bi grows epitaxially and the P–Bi bond length is 2.42±0.05 Å. The first P–In nearest neighbor distance is determined as 2.46±0.05 Å, which is almost equal to the P–In bond length for the clean InP(110) surface and the bond length is 3% contracted in comparison to its value for bulk InP. Note that the surface states for the clean InP(110) surface are pushed out of the band gap due to surface relaxation. Hence, the interface states due to the atomic geometries of the substrate at the interface may not influence Schottky barrier formation to cause Fermi-level pinning. The P–P and P–Bi bond lengths in the second near-neighbor distance were determined as 4.17±0.06 and 4.26±0.06 Å, respectively.
Band bending at low-temperature metal/III–V semiconductor interfaces: The overshoot phenomenon
Authors: Miyano K. E. , Cao R. , Spindt C. J. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

In a recent paper Hecht pointed out the influence of photovoltaic band flattening on photoemission measurements of Schottky barrier formation [M. H. Hecht, J. Vac. Sci. Technol. B 8, 1018 (1990)]. He further suggested that the low-temperature (LT) overshoot observed on high-doped p-GaAs is due to photon-induced charging of the GaAs surface. In this paper we evaluate this hypothesis based on a variety of LT band bending data. We conclude that the charging hypothesis fails to explain the following key aspects of the overshoot data. (1) The overshoot is dependent on the temperature of the interface formation and its influence on adatom clustering rather than the temperature at which the measurement is made. (2) The degree of overshoot has a simple dependence on the adatom ionization potential and electronegativity. (3) The overshoot is observed on very high doped substrates in which tunneling is anticipated to restore any nonequilibrium surface charge. A model involving adsorbate-induced donor states at the overshoot level in the gap provides a more straightforward and complete explanation of these and other aspects of the overshoot data.
The etching of CHF3 plasma polymer in fluorine-containing discharges
Authors: Bariya Anand J. , Shan Hongqing , Frank Curtis W. , Self Sidney A. , McVittie James P.
Published: July 2002

The etching of CHF3 plasma polymer in fluorine containing electrical discharges was studied. The fluorine sources were SF6, CF4, and mixtures of the two. For discharges in SF6 and mixtures of SF6 and CF4, a good correlation was obtained between the etch rate and the atomic fluorine concentration measured using actinometry. For CF4, the etch rate was found to be much higher than that predicted from this correlation. This is attributed to the energetic ion bombardment of the polymer surface in the CF4 discharge. X-ray photoelectron spectroscopy analysis of the etched polymer surface shows an increased fluorine content, but the F:C ratio was independent of the etching conditions. The implications of the results for the kinetics of fluorocarbon plasma polymerization are discussed.
Plasma parameter and etch measurements in a multipolar confined electron cyclotron resonance discharge
Authors: Mantei T. D. , Ryle T. E.
Published: July 2002

A multipolar confined electron cyclotron resonance discharge has been characterized by plasma parameter and etch measurements in Ar and SF6. Positive ion densities of 1011 cm−3 or greater are obtained at pressures of 0.1–1.0 mTorr with 400–600 W input microwave power. The positive ion current density uniformity across a 16 cm diam is ±4% at 1.0 mTorr. Silicon etch rates of 0.25–1.25 μm/min are obtained with 0.1–1.0 mTorr of SF6, with −60 V substrate bias.
Prospects for x-ray lithography
Authors: Fleming D. , Maldonado J. R. , Neisser M.
Published: July 2002

The essentials of proximity x-ray lithography (XRL) have been established and successful alternative implementations have been demonstrated in academic and industrial laboratories worldwide. Results continue to show that XRL can provide simpler and more robust processes than optical or electron beam alternatives. And it is widely accepted that this becomes more true as lithographic dimensions shrink. So why do we still await the introduction of the first commercial use of XRL? Use of a new technology requires its either attaining the unattainable or excelling at cost/performance. For near term application, XRL must leap the latter hurdle. While most concede the superior robustness of XRL to normal process variation, popular lore has it that availability or an adequate infrastructure limits XRL becoming a process of choice. We discuss the current state of XRL against this competitive challenge and project progress forward. In so doing, we find that XRL is now approaching a critical crossroad. While optical approaches struggle to demonstrate technical realization and electron beam approaches are losing ground in the pixel per chip per second race, XRL’s challenge is to mature its infrastructure sufficiently to attract proponents eager to make it the process of choice. The pace of XRL efforts leads us to the conclusion that XRL can be the process of choice for 250 nm applications, most probably beginning with 256 Mb DRAM or NVRAM.
Characterization of InxGa1−xP/GaAs grown by gas source molecular-beam epitaxy (0.35≤x≤0.60) by spectroscopic ellipsometry
Authors: Biswas D. , Lee H. , Salvador A. , Klein M. V. , Morkoç H.
Published: July 2002

The InGaP/GaAs system presents an attractive alternative to the GaAs/AlGaAs system for heterojunction devices because of its unique heterojunction properties and relatively small interface recombination velocity. A lack of sufficiently detailed optical characterization for probing the higher bands, however, led us to undertake an investigation utilizing spectroscopic ellipsometry. Samples studied were grown on (100) GaAs substrates by gas source molecular-beam epitaxy. The low-temperature photoluminescence linewidth was as narrow as 6.7 meV. Hall measurements showed a room-temperature electron mobility of 1500 cm2/V s and unintentionally doped ‘‘n’’-type carrier concentration of 1.7 × 1016 cm−3. The compositional dependence of the E1 gap of InxGa1−xP near lattice-matching conditions to the GaAs buffer for (0.35≤x≤0.60) and the broadening of the E1 gap have been studied utilizing the spectroscopic ellipsometry technique for the first time. The position of the E1 gap is found to be sensitive to growth conditions.
Samarium doping of molecular-beam epitaxially grown InSb on InP
Authors: Partin D. L. , Heremans J. , Thrush C. M. , Morelli D. T.
Published: July 2002

We report here on the transport properties epitaxial InSb films grown by molecular-beam epitaxy and doped with Sm in the atom density range from 6.1×1016 cm−3 to 3.2×1018 cm−3 at temperatures between 40 and 400 K. Sm is a donor for InSb. The samples were grown at a flux ratio Sb/In=1.07±0.03. For Sm concentrations below 5×1017 cm−3, 25 atoms of Sm give one extrinsic electron. Samples grown with higher Sm concentrations have extrinsic electron densities around 1×1017 cm−3. At low temperatures (T<150 K), the electron mobility increases with doping concentration up to rare-earth densities of 3×1017 cm−3; at higher rare-earth concentrations, the mobility decreases again. At room temperature, the mobility decreases monotonically with increasing Sm concentration. Very similar results are observed on InSb films doped with Er. We point out that impurity charge ordering was invoked to explain similar observations made on HgSe:Fe.
In situ passivation of GaAs after BCl3/Cl2 reactive ion etching
Authors: Yoon Euijoon , Gottscho Richard A. , Donnelly Vincent M. , Hobson William S.
Published: July 2002

Reactive ion etching (RIE) of compound semiconductors is well-known to produce damaged surfaces that reduce quantum yield and produce excessive leakage currents. Therefore, it is desirable to develop procedures to passivate or remove such process-induced damage. From a manufacturing perspective, it would be ideal to perform such postetch passivation in situ. In this work, we use real-time photoluminescence monitoring and ex situ x-ray photoelectron spectroscopy to evaluate the effectiveness of in situ H2 plasma passivation of GaAs after RIE in a BCl3/Cl2 plasma. Because of reactor wall contamination, we conclude that in situ passivation, at least for this chemical etching system, is not practical; two chambers are needed, one for etching and another for passivation. However, RIE damage is removed effectively by first stripping the Cl-contaminated GaAs surface using an acid solution and then exposing the resultant oxidized surface to the H2 plasma. This procedure results in an elevated quantum yield that remains stable in air indefinitely.
Simulation of the effect of thin film microstructure on current and temperature distributions in very large scale integrated metallization structures
Authors: Smy T. , Reny D. J. , Brett M. J.
Published: July 2002

A two-dimensional finite element program is used to solve current and temperature distributions in inhomogeneous aluminum and tungsten metal lines deposited over very large scale integrated topography. Microstructure depictions of both aluminum and tungsten lines are obtained using the process simulator simbad. Density information is then used to calculate conductivity profiles as input to the current and temperature solver simcat. Experimental results are used to calculate and correct for the cooling in the third dimension of the simulation and results are presented regarding the effect of substrate and passivation thickness on line heating. Two examples of the effect of topography and microstructure on the flow of current and heating within metal lines are presented. Aluminum and tungsten lines are deposited over a series of trenches of varying sidewall angle, and the line temperature and maximum current stress are plotted as a function of this angle. The lower density of the tungsten deposited on the sidewalls of the trench is determined to have a significant effect on the operating temperature of the metal line. As a second example the current distribution is compared between two aluminum lines deposited at different substrate temperatures over a 1 μm trench with vertical sides.
Chemical vapor deposition tungsten via plug process development with polyimide interlevel dielectric in a multilevel metal system
Authors: Chang Li-Hsin , Weston Don , Sellers Jim
Published: July 2002

Both blanket and selective chemical vapor deposition (CVD) W via plug processes have been evaluated in a multilevel metallization system using a low (≤3.0) dielectric constant fluorinated polyimide as the interlevel dielectric (ILD) material. In the blanket CVD W deposition and etchback process, the sputter deposition conditions for the Ti–W ‘‘glue’’ layer prior to the CVD W deposition were found crucial to the success of the process. An in situ high temperature sputter etch and prebake eliminated a metal–polyimide ‘‘bubbling’’ problem. A Ti–W film with moderately tensile stress is required to prevent polyimide from ‘‘wrinkling’’ and ‘‘cracking’’ during the subsequent CVD W deposition step. In the selective W process, excellent selectivity resulted with polyimide ILD compared to silicon dioxide; however, tungsten growth ‘‘inhibition’’ on Ti–W or W metal in the polyimide via was experienced and was difficult to overcome.
Stoichiometry- and bond-structure-dependent decomposition of trimethylgallium on As-rich GaAs(100) surfaces
Authors: Sasaki Masahiro , Yoshida Seikoh
Published: July 2002

The decomposition of trimethylgallium (TMG) on an As-rich GaAs(100) surface associated with the surface stoichiometry has been investigated using mass spectrometry and reflection high-energy electron-diffraction observations. Surfaces with different stoichiometries are prepared by depositing metal Ga on well-defined GaAs surfaces. It has been found that the TMG decomposition strongly depends on the surface stoichiometry; even such a low Ga coverage difference as 0.01 monolayer induces a surface decomposition enhancement. The TMG decomposition rate is lowest on a surface that shows the most distinct 2×4 reconstruction, which is the most stable structure. The role of the surface structure in TMG decomposition is also discussed.
High-spatial-resolution resistivity mapping applied to mercury cadmium telluride
Authors: Kopanski Joseph J. , Lowney Jeremiah R. , Novotny Donald B. , Seiler David G. , Simmons Art , Ramsey John
Published: July 2002

The fine-scale resistivity variations of slices of bulk, n-type Hg1−xCdxTe (HgCdTe) grown by the solid-state recrystallization (SSR) process and thin-film epitaxial layers of HgCdTe grown by liquid phase epitaxy (LPE) on SSR substrates were mapped at room temperature (297 K). An automatic probe station was used to make four-probe resistance measurements, spaced 80 μm apart, on lithographically defined metal-to-HgCdTe contacts. Most slices of SSR HgCdTe were found to have resistivities that increased from the center to the outside edge, and some SSR material also showed small inclusions with resistivity either higher or lower than the surrounding material. LPE material was found to have a more random variation in resistivity than SSR HgCdTe material. Also, the metal–semiconductor contact resistivity of In/Pb/In/Ni contacts to n-type HgCdTe was measured to be in the range of 0.3 to 20×10−5 Ω cm2 for HgCdTe resistivities varying from 0.01 to 0.1 Ω cm.
Magnetic generation of electrons and holes in semimetallic HgTe–CdTe superlattices
Authors: Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Wojtowicz T. , Dobrowolska M. , Furdyna J. K. , Chu X. , Faurie J. P. , Ram-Mohan L. R.
Published: July 2002

We predict theoretically, on the basis of field-dependent band structure considerations, that it should be possible to generate a high-density electron-hole plasma in semimetallic HgTe–CdTe superlattices simply by applying a magnetic field. When the field is above a critical value, minority carriers should coexist with majority carriers in the zero-temperature limit, with both densities increasing as B−Bcrit. Experimental confirmation of this unique effect is provided by low-temperature magneto-optical data showing the emergence of minority holes in two n-type superlattices whenever B≥Bcrit.
Direct determination of impact ionization rates near threshold in Al0.9Ga0.1As and GaAs using molecular-beam epitaxially grown GaAs/Al0.9Ga0.1As structures and soft x-ray photoemission
Authors: Eklund E. A. , Kirchner P. D. , Shuh D. K. , McFeely F. R. , Cartier E.
Published: July 2002

The line shape of the Al 2p core-level photoemission peak in Al0.9Ga0.1As is found to be strongly dependent on the electron kinetic energy. Using Monte Carlo transport simulations it is shown that the observed strong, asymmetric line broadening is caused by electron–phonon scattering. In agreement with the experimental observations, the simulations predict that this phonon induced line broadening is rapidly suppressed as the core line is shifted through the impact ionization threshold. Thus, it becomes possible to infer from the core-level line shape the energy dependent impact ionization rates near the impact ionization threshold. In addition, the impact ionization rates in GaAs are computed from intensity measurements which probe the Al 2p core-level attenuation in the GaAs overlayers used to chemically terminate the samples. These results are compared to calculated rates from the literature.
Hydrogen content of silicon and thermal oxidation induced moisture generation in an integrated rapid thermal processing reactor
Authors: George M. A. , Bohling D. A. , Wortman J. J. , Melzak J. A. , Hames G. A.
Published: July 2002

The thermal oxidation of CZ-grown p(100) Si has been investigated in the temperature range of 400–1000 °C in a rapid thermal processing reactor. In this study we present the results of investigating chemical analysis of the process gases entering and exiting the reactor. This arrangement enables us to investigate the effects of impurities intentionally doped into the process gas stream and to measure process generated products. In this article we discuss the results of measuring H2 and H2O during preoxidation anneal in ultrahigh purity (UHP) Ar and during thermal oxidation in UHP O2. As a result of these analyses, we have experimentally determined the quantity of hydrogen contained in as received virgin CZ-grown p(100) Si wafers. This content is measured as 2.95×1017 atoms/cc.
Dry processed, through-wafer via holes for GaAs power devices
Authors: Pearton S. J. , Ren F. , Katz A. , Lothian J. R. , Fullowan T. R. , Tseng B.
Published: July 2002

The fabrication of through-wafer via holes in GaAs substrates by plasma etching and laser drilling is reported. Using a low pressure (15–20 mTorr), low dc bias (−150 V) Cl2/BCl3 discharge with Cl2-to-BCl3 ratios ≤0.2, we are able to produce narrow (≤30 μm) via holes. This enables the use of a higher density of vias in closer proximity to the active GaAs power devices than can be achieved with normal diameter (100–150 μm) holes. Microwave enhancement of the plasma density using an electron cyclotron resonance source increases the GaAs vertical and lateral etch rates and requires use of low Cl2-to-BCl3 ratios in order to retain the anisotropic nature of the vias. Multiple pass (∼100 per hole) drilling of vias with a Q-switched Nd-YAG frequency doubled (532 nm), 30 mW laser has also successfully produced through-wafer connections. This provides a maskless, versatile method for producting vias customized for a particular wafer, but is less developed than plasma etching.
Fabrication and characterization of electron beam evaporated silicon field emitter arrays
Authors: Myers G. P. , Aslam M. , Klimecky P. , Cathey L. W. , Elder R. E. , Artz B. E.
Published: July 2002

This article describes the fabrication process for, and electrical characterization of, electron beam evaporated silicon field emitter arrays in a diode configuration. Each array consists of 2000 unsharpened, n-type, polycrystalline emitters. The process produces 80–90 such arrays spaced 9 mm apart and isolated from each other on a 4 in. wafer. In addition, a method for completing an anode structure is shown that circumvents the need for small scale probing of the tips in order to demonstrate field emission. Many of the arrays exhibited diode characteristics and Fowler–Nordheim emission behavior with turn-on voltages of ∼80 V. Emitter tip radius was calculated from the slope of the Fowler–Nordheim plot to be in the range of 10–12 nm.
300 kHz pulse plasma etching of GaAs using a mixture of ClCH3 and H2
Authors: Law V. J. , Tewordt M. , Clary D. C. , Jones G. A. C.
Published: July 2002

A new process for low-frequency (300 kHz) pulse plasma etching of GaAs and mask materials (Au, Cu, and Ni) using a mixture of ClCH3 and H2 in the pressure range of 40–80 mTorr is reported. The ion-bombardment ri and chemical component rc of the etch rate are deconvolved by measuring the GaAs etch rate as a function of pulse width, duty cycle, pressure, and etch time constant t1/2. The etch rate is modeled using a phenomenological rate equation with fitting parameters: t1/2, ri, and rc.
Model for predicting the effects of device geometry on the capacitance of field emitter array cathodes
Authors: Ohlinger W. L. , Hill D. N. , Feeney R. K. , Munné V.
Published: July 2002

Successful application of field emitter array cathodes at microwave frequencies is dependent upon significant progress in emitter development. Two factors are of primary concern, namely, the transconductance and the array capacitance. To provide guidance in development of structures with minimum capacitance, a scaled, physical model of an emitter array has been developed and used to study qualitatively the effect of several geometrical and materials parameters on device capacitance. In this article the effects of an insulating versus a conducting substrate, and variation of the insulator film thickness, extractor aperture diameter, and extractor film thickness are reported. It is shown that the array capacitance is primarily determined by the details of the extractor aperture–emitter tip geometry, and is not influenced by the extractor to substrate spacing unless the insulator film thickness is substantially less than one-half the pin-to-pin spacing in the array. Although the results are not intended to be quantitative, it is estimated that the Georgia Tech field emitter array cathodes, based on oxide–metal composite materials composed of single-crystal tungsten emitter tips in an insulating zirconium dioxide matrix (substrate), display capacitances of the order of 1×10−16 Farads/pin.
Modeling of multilayer ion etching processes
Authors: Sherwin S. J. , Barouch E. , Karniadakis G. E. , Orszag S. A.
Published: July 2002

Numerical simulation is used to model ion etching in trilayer lithography. The simulations are capable of capturing the evolution of the boundary between two materials as well as the physically observed phonemena reactive ion etching lag and undercutting. Numerical results are compared with experimental data and a good agreement is found except close to the material interface where the slope of the surface is large. This error is attributed to a purely energy dependent yield used in the simulations.
Influence of surface roughness on the electrical properties of Si–SiO2 interfaces and on second-harmonic generation at these interfaces
Authors: Bjorkman C. H. , Yasuda T. , Shearon C. E. , Ma Y. , Lucovsky G. , Emmerichs U. , Meyer C. , Leo K. , Kurz H.
Published: July 2002

Si(111) wafers, cut at angles between 0° and 5° in the [112̄] direction, were prepared by a standard RCA cleaning process followed by a rinse in HF/NH4F solutions with different pH values. Si–SiO2 structures were formed on these surfaces by a two-step low-temperature plasma-assisted oxidation/deposition process, and compared with interfaces formed by thermal oxidation, followed by rapid thermal annealing. The Si(111)–SiO2 interface, subjected to predeposition rinse in a 40 wt. % NH4F solution, displayed a midgap interface trap density Dit of ∼4×1010 cm−2 eV−1. The Dit values increased systematically up to ∼2×1011 cm−2 eV−1 as the pH of the final rinse was decreased. Using a second-harmonic generation pumped at 1053 nm, the influence of off-axis orientation and surface structure of Si(111) surfaces was examined. The surface structure was modified by thermal oxidation at 850 °C, annealing at temperatures in the range of 900–1100 °C, and removing the oxide in a HF solution. Changes in the characteristic rotational anisotropy are analyzed using harmonic functions reflecting the onefold and threefold symmetry of vicinal Si(111) surfaces, and are compared with changes in the thermal oxide Dit values on annealing.
Towards a physical understanding of spreading resistance probe technique profiling
Authors: Snauwaert J. , Hellemans L. , Czech I. , Clarysse T. , Vandervorst W. , Pawlik M.
Published: July 2002

Spreading resistance has become a standard in semiconductor resistivity determination. The method is based on metal–semiconductor point contact measurements. The resulting spreading resistance is generally described by Rs=ρ/4a, wherein ρ refers to the bulk resistivity and a to the radius of the contact area. This relation is only valid in the ideal case where the contact area can be considered as a homogenous circular contact. New contact models have introduced the concept of multiple microcontacts in spreading resistance probe technique (SRP) measurements. The physical nature of these contacts has now been studied by an atomic force microscope (AFM). The AFM images show indentations of multiple point contacts penetrating 10–100 nm into the silicon depending on the applied force and the probe characteristics. Time-dependent measurements at constant force revealed a gradual increase in penetration depth and in contact area. An AFM with conducting tip has been developed to study the behavior of a single contact point. I–V curves for such a metallic tip are compared with I–V curves for standard SRP probes.
Survey of high-voltage pulse technology suitable for large-scale plasma source ion implantation processes
Authors: Reass William A.
Published: July 2002

Many new plasma processes ideas are finding their way from the research lab to the manufacturing plant floor. These require high voltage (HV) pulse power equipment, which must be optimized for application, system efficiency, and reliability. Although no single HV pulse technology is suitable for all plasma processes, various classes of high voltage pulsers may offer a greater versatility and economy to the manufacturer. Technology developed for existing radar and particle accelerator modulator power systems can be utilized to develop a modern large scale plasma source ion implantation (PSII) system. The HV pulse networks can be broadly defined by two classes of systems, those that generate the voltage directly, and those that use some type of pulse forming network and step-up transformer. This article will examine these HV pulse technologies and discuss their applicability to the specific PSII process. Typical systems that will be reviewed will include high power solid state, hard tube systems such as crossed-field ‘‘hollow beam’’ switch tubes and planar tetrodes, and ‘‘soft’’ tube systems with crossatrons and thyratrons. Results will be tabulated and suggestions provided for a particular PSII process.
Bright visible photoluminescence of spark-processed Ge, GaAs, and Si
Authors: Ludwig M. H. , Hummel R. E. , Chang S.-S.
Published: July 2002

High-frequency spark discharges were applied to single-crystalline wafers of Ge, GaAs, and Si. The spark-processed (sp-) samples were characterized by photoluminescence (PL) and Raman measurements. Strong and stable luminescence with wavelengths centered at 416 and 525 nm was observed in sp-Ge and sp-Si layers, respectively, when excited with a 325 nm laser beam. A considerable blue shift of the PL (compared to the unsparked specimen) was also detected for sp-GaAs with an average peak wavelength around 500 nm. The Raman shifts of the spark-processed materials indicate that nanocrystals were formed, having diameters of 3.5–4 nm for Si and about 6 nm for Ge. A correlation between the PL wavelengths, the nanocrystal sizes, and the different semiconductor materials has been established based on the effective-mass approximation. Making use of this model the nanocrystallite sizes have been found to range between ∼3 nm for Si and ∼5 nm for Ge. The related wavelengths for optical transitions confirm the PL results. The findings support the quantum confinement model.
Growth of beryllium doped AlxGa1−xAs/GaAs mirrors for vertical-cavity surface-emitting lasers
Authors: Peters M. G. , Thibeault B. J. , Young D. B. , Gossard A. C. , Coldren L. A.
Published: July 2002

We experimentally compare a variety of techniques used in the growth of p-type Be doped AlxGa1−xAs/GaAs distributed Bragg reflector (DBR) mirrors to reduce the operating voltages of vertical-cavity surface-emitting lasers (VCSELs). The AlxGa1−xAs composition, average doping concentration, grading and doping profile at the interfaces, and growth temperature are all important parameters to achieve low voltage mirrors with low optical loss and high thermal conductivity. Specifically we examine band-gap engineering techniques to flatten the voltage barrier at the DBR mirror layer interfaces. We demonstrate VCSELs with low operating voltages (1.7–3.0 V) and high continuous wave room-temperature power-conversion efficiencies and output powers.
Investigation of modulated radio frequency plasma etching of GaAs using Langmuir probes
Authors: Law V. J. , Braithwaite N. St. J. , Ingram S. G. , Clary D. C. , Jones G. A. C.
Published: July 2002

Radio frequency ClCH3/H2 plasma etching of GaAs is examined in the 10–140 mTorr pressure range using square-wave modulation of the excitation source to control the etching. A Langmuir probe is used to measure time-resolved electron density, characteristic temperature, and floating potential during the plasma afterglow period. The ClCH3/H2 plasma electron energy is found to be 1.2±0.3 eV. The near afterglow plasma density decay has a time constant in the order of τ=30 μs at 140 mTorr for 10%–20% ClCH3 in H2 and τ=100 μs for H2. The floating potential continues to decay into the far afterglow, with a characteristic time of the order of milliseconds. The Langmuir probe measurements indicate that in ClCH3 plasmas the near afterglow is dominated by electron attachment, whereas the far afterglow is dominated by ambipolar diffusion. The GaAs etch rate experiments show that surface reactions continue into the far afterglow, dominating the behavior of the time average etch rate.
Formation of nanometer-sized Au dots on Si substrate in air
Authors: Hosaka Sumio , Koyanagi Hajime , Kikukawa Atsushi , Maruyama Yohji , Imura Ryou
Published: July 2002

Nanometer-sized Au (gold) dots on a Si substrate were formed by field evaporation using an atomic force microscope (AFM) in air. Theoretical and experimental studies show that field evaporation is possible in the AFM metal probe/vacuum/thin insulator/conductor configuration. Theoretically, the field evaporation is generated by further application of an additional bias voltage less than 30–40 V in a thin insulator. Experiments demonstrated that ultrasmall gold dots were formed on a natural SiO2/Si substrate by the applied voltage less than 10 V, and ultrasmall gold dots of 15 nm in diameter were made on the insulator.