bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive ion etching induced damage with gas mixtures CHF3/O2 and SF6/O2
Authors: Wu W. , McLarty P. K.
Published: July 2002

In this work, reaction ion etching (RIE) induced damage and its impact on device performance have been characterized and evaluated using a variety of characterization techniques for two technologically important gas mixtures: CHF3/O2 for selective oxide etching, and SF6/O2 for selective poly Si or crystalline Si etching. Current–voltage characteristics of Al/Si Schottky diodes fabricated on the RIE exposed Si surface reveal significant barrier height shifts for the CHF3/O2 process while showing little change for the SF6/O2 processes. Carrier generation lifetime is degraded by at least one order of magnitude, with the degradation due to CHF3/O2 processes being more severe. Scanning electron microscopy and Auger electron spectroscopy support the idea that the defects that give rise to the altered electrical behavior are most likely Si lattice damage instead of metal contamination and/or morphologic modification. Rapid thermal annealing of the CHF3/O2 etched samples has a negative effect on I–V recovery precluding simple application of RTA for removing RIE damage. In the RIE exposed oxide, the two distinctively different gas mixtures induce very similar C–V and Si/SiO2 interface property changes, suggesting that the high energy photons present in the plasma glow are the most probable source of damage in the oxide.
Manifold arsenic and phosphorus effusion source for GaAsP alloys
Authors: Wood C. E. C. , Johnson F. G. , Tabatabaei S. A.
Published: July 2002

We describe an independently valved solid arsenic and phosphorus effusion source for molecular beam epitaxy. A common posteffusion hot zone and orifice ensure constant flux ratios of arsenic, phosphorus, and mixed species in the beam. With this source, we have demonstrated molecular beam epitaxial growth of GaAs1−xPx layers with better than ±0.4% compositional variation over a 3-in.-diam substrate.
Effect of 20–95 eV Ar ion bombardment of GaAs(001): In pursuit of damage-free ion-assisted growth and etching
Authors: Mirecki Millunchick J. , Hultman L. , Barnett S. A.
Published: July 2002

Defect generation due to very-low-energy ion bombardment of GaAs(001) has been studied. Ar+ bombardment was performed at energies E=20–95 eV and current densities J=0.1–0.75 mA/cm2 on surfaces maintained at 615 °C in an As4 flux, both without growth and during GaAs molecular beam epitaxy. Reflection high-energy electron diffraction patterns exhibited 2×4 reconstruction and strong Kikuchi lines, indicative of flat ordered surfaces, independent of E and J. Cross-sectional transmission electron microscopy showed that subsurface dislocation loops were generated when E≥55 eV. The defect density increased with increasing E and J. Films grown with E≤50 eV were free of extended defects, showing that the beneficial effects of ion-assisted molecular beam epitaxy can be achieved without causing ion damage. Measurable sputtering rates were observed for E≥50 eV at J=0.5 mA/cm2.
Atomically resolved scanning tunneling microscopy study of the adsorption and dissociation of methylchloride on Si(001)
Authors: Bronikowski Michael J. , Hamers Robert J.
Published: July 2002

The room-temperature adsorption and dissociation of methylchloride (CH3Cl) on Si(001) using scanning tunneling microscopy has been studied. Fragments are identified by the symmetry of their binding on the underlying Si(001) lattice. Methylchloride adsorbs dissociatively at room temperature, yielding a methyl group and a chlorine atom bound to the surface. Chlorine atoms bind in a variety of geometries, the most common being two chlorine atoms bonded to a single silicon dimer (silicon monochloride dimers). When the surface is heated to 150 °C, all Cl rearranges to this monochloride-type bonding configuration, and images reveal the beginnings of monochloride island formation. The Cl:CH3 ratio on the surface is found to be approximately 2:1, implying that not all methyl groups are bound to the surface in the reaction.
Model for a large area multi-frequency multiplanar coil inductively coupled plasma source
Authors: Yamada Naoki , Ventzek Peter L. G. , Date H. , Sakai Y. , Tagashira H.
Published: July 2002

A model for a large area multifrequency multiplanar coil inductively coupled plasma (ICP) source is presented. Typical ICP sources employ a single coil that is engineered to provide optimum plasma uniformity for large area processing. Pulsed sources have also been developed to improve etch selectivity via increased radical generation and lower net ion densities. The source described here potentially achieves a combined pulsed mode and the capability of moving the plasma source from inner to outer radii in a controlled fashion (raster mode) for very large area applications. The model consists of a coupled steady-state two-dimensional ambipolar diffusion model, an electromagnetics model, and a lumped parameter circuit model. While stable operation is possible, the model shows that the scheme is found to be very sensitive to coil-to-coil coupling and to the ordering of the phases and frequencies of the coils. Examples of stable operation of a three coil set device are presented. Results suggest that frequency control may be an attractive control variable for real time control of large area plasma processes.
Comparison of tribological properties of carbon and carbon nitride protective coatings over magnetic media
Authors: Khurshudov Andrei , Kato Koji , Daisuke Sawada
Published: July 2002

According to theoretical predictions made in 1989–1990, carbon nitride can be even harder than diamond. Carbon nitride thin films may become a good competitor for diamondlike carbon, which possesses a high hardness, high wear resistance, and low friction coefficient. At present, there are only a few studies on the tribology of CNx coatings. Tribological properties of the deposited by means of ion beam assisted deposition carbon nitride coating (90%C–10%N) were compared with those of commercial carbon coatings at macro- and microscales. CNx coating on a magnetic rigid disk showed both lower macro- and microfriction compared with that of a carbon coating in unlubricated sliding against a silicon nitride pin. The life of the CNx coating was about three to ten times longer than the life of carbon coatings.
Native and modified uncoated neurons observed by atomic force microscopy
Authors: Cricenti A. , De Stasio G. , Generosi R. , Scarselli M. A. , Perfetti P. , Ciotti M. T. , Mercanti D. , Casalbore P. , Margaritondo G.
Published: July 2002

Dried, fixed uncoated neuron granule cells and their neurites have been imaged in air by an atomic force microscope (AFM) in the repulsive regime of contact mode. Neurons have also been observed after swelling with glutamate or decapping. Modifications induced by glutamate resulted in a drastic reduction in the cell body height (from 1.5 to 2.0 μm for the untreated ones down to 0.7–1.0 μm) and in an increased corrugation of the granule cell membrane. In the decapped neurons AFM revealed decreasing cell body height for an increasing amount of removed material during the decapping procedure. These results demonstrate that AFM is the ideal technique to observe cell corrugation and height modifications during cell treatments of neurobiological interest.
Synthesis of carbon nitride films at low temperatures
Authors: Hammer P. , Baker M. A. , Lenardi C. , Gissler W.
Published: July 2002

Carbon nitride films (CNx) have been deposited by sputtering a graphite target with nitrogen ions. Films were grown both with and without the presence of an assisting focused N2 ion beam. The sputter beam voltage was varied between 150 and 1500 V and the applied assisting beam voltage from 80 to 500 V. The substrate was held at fixed temperatures between 80 and 673 K. The coatings were characterized with respect to their electrical, optical, and structural properties. The nitrogen content was measured by x-ray photoelectron spectroscopy (XPS) and a maximum nitrogen concentration of 44 at. % was obtained for a nonassisted sample deposited at 140 K. The chemical structure was investigated by XPS and Fourier transform infrared spectroscopy. Reduction of the substrate temperature in conjunction with low sputter beam voltages (<200 V) caused the optical band gap to increase up to 2.2 eV, the sheet conductivity to decrease to less than 10−9 (Ω cm)−1 and the density to be reduced to 1.6 g/cm3. The increasing transparency is accompanied by structural changes indicating a transition from a predominantly sp2 bonded amorphous sp2/sp3 C–N network to a more linear polymerlike structure consisting predominantly of doubly and triply bonded C and N atoms. No evidence for the formation of the β-C3N4 phase was found.
Study of TiOxNy thin film selective surfaces produced by ion assisted deposition
Authors: Bittar A. , Cochrane D. , Caughley S. , Vickeridge I.
Published: July 2002

Thin films of titanium oxynitride were produced by ion assisted deposition of titanium using different nitrogen to oxygen ion ratios. X-ray, Raman, nuclear reaction analysis and Rutherford backscattering spectroscopies were used to study the film structure and to establish the relationship between deposition conditions, film composition, and electrical and optical properties of the films in the visible and infrared. This method of deposition appears to yield hard, amorphous, and uniform films with a restricted compositional range near the equistoichiometric composition. Nevertheless, variations in oxygen content of the films can result in changes in the electrical and optical properties that are sufficiently large to enable their use as selective surfaces.
Combined x-ray photoelectron/Auger electron spectroscopy/glancing angle x-ray diffraction/extended x-ray absorption fine structure investigation of TiBxNy coatings
Authors: Baker M. A. , Mollart T. P. , Gibson P. N. , Gissler W.
Published: July 2002

Ti–B–N coatings with stoichiometries corresponding to a region of the phase diagram in which a three phase TiB2+TiN+BN composition is predicted, have been deposited by reactive magnetron sputtering. Characterization of the films by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), glancing angle x-ray diffraction (GAXRD), and extended x-ray absorption fine structure (EXAFS) has been performed to provide information on chemical composition and microstructure. GAXRD and EXAFS have shown the Ti based phases to be dominated by the presence of nanocrystalline TiB2, the grain size of which decreases to an unmeasurably low value with increasing N content. Evidence of TiB2, TiN, and BN bonding is found in the XPS spectra and the inferred phase composition has been found to be in good agreement with that predicted by the phase diagram. From XPS and AES spectra, the BN phase present has been concluded to be of the hexagonal type.
Antimony adsorption on the Si(111) surface with the 7×7 and √3×√3-Ga structures studied by scanning tunneling microscopy
Authors: Kusumi Yukihiro , Fujita Ken , Ichikawa Masakazu
Published: July 2002

Scanning tunneling microscopy is used to study the initial stage of Sb adsorption on Si(111) surfaces with the 7×7 and √3×√3-Ga structures. It has been found that Sb is preferentially adsorbed on the 7×7 regions at 430 °C, owing to the difference in the chemical reactivity and the Sb diffusivity between two reconstruction surfaces. Using this phenomenon, stripe patterns with the Sb-adsorbed 56-nm-wide 7×7 regions and 35-nm-wide √3×√3-Ga regions are formed for a demonstration of a selective adsorption of Sb on the nanometer scale.
Analysis of interface roughness’s effect on metal–oxide–semiconductor Fowler-Nordheim tunneling behavior using atomic force microscope images
Authors: Lin Heng-Chih , Ying Ji-Feng , Yamanaka Toshiyaki , Fang Simon J. , Helms C. R.
Published: July 2002

For the first time, metal–oxide–semiconductor interface atomic force microscope images were used to directly calculate the Fowler-Nordheim tunneling behavior for thin gate oxides with different interface roughness. Assuming that the roughness is conformal on both interfaces, surface curvature and electric field distribution were used to calculate the tunneling current density caused by low spatial frequency roughness. On the other hand, a three-dimensional Laplace solver and a quasi-one-dimensional Fowler-Nordheim equation were used to calculate the tunneling current contributed by high spatial frequency roughness. Considering contributions due to both high and low spatial frequency roughnesses, we found good agreement between the theoretical calculation and experimentally measured tunneling current–voltage curves. This simulation indicates that oxide thinning is probably not the main reason for the increase of tunneling current in the thin oxide (∼6 nm) range. The higher surface electric field due to roughness curvature itself is most likely responsible for this increase.
Characterization of magnetron-sputtered partially ionized aluminum deposition
Authors: Hayden D. B. , Juliano D. R. , Green K. M. , Ruzic D. N. , Weiss C. A. , Ashtiani K. A. , Licata T. J.
Published: July 2002

A rotating magnet dc planar magnetron with a 33-cm diameter aluminum target is coupled with a secondary plasma source to ionize the sputtered metal neutral flux to control the angular distribution of the flux arriving at the surface of the substrate. For this purpose, a radio-frequency (rf) plasma is created between the sputtering target and substrate by a three-turn coil located in the vacuum chamber. The rf plasma increases the electron temperature and density, which results in significant ionization of the neutral metal flux from the sputtering target. By applying a small negative bias to the substrate, metal ions are drawn to the substrate at normal incidence. A gridded energy analyzer and a quartz crystal microbalance (QCM) were used to determine the ion and neutral deposition rates. From this, the ionization fraction of the flux incident onto the QCM is determined.
The morphology of duplex and quadruplex DNA on mica
Authors: Muir Tera , Morales Emily , Root Jeffrey , Kumar Indira , Garcia Brian , Vellandi Christian , Jenigian Dena , Marsh Thomas , Henderson Eric , Vesenka James
Published: July 2002

Atomic force and low current scanning tunneling microscopy characterization of duplex and quadruplex DNA (“G-wire”) morphology adsorbed on to mica reveals very different topography. This observation contradicts similar dimensions for the two molecules as determined by spectroscopic techniques. In the work presented here, the diameter of duplex DNA, as measured by height above the mica background, was 25% of that observed by x-ray crystallographic methods. However, the G-wire diameter was similar to that determined by nuclear magnetic resonance and crystallographic methods. These observations appear to be independent of the residual buffer or scanning probe microscopy (SPM) technique used. The SPM observed widths of these molecules are similar and supports a model in which duplex DNA is pinned flat to the mica substrate. These morphological differences may be related to the variations in intermolecular forces with the mica substrate and intramolecular forces holding the polymers together.
Reemission of sputtered refractory metals during deposition
Authors: Tait R. N.
Published: July 2002

Refractory metals are of interest for use in diffusion barriers and adhesion layers in ultra-large-scale integrated circuit metallization. An interesting feature of many of these materials is the reemission of some of the deposited flux during sputtering. This can be useful in depositing conformal layers in high aspect ratio contacts and vias. Overhanging structures have been used to study reemission in TiW, Ti, Nb, W, Ta, and Pt sputtering. While Ti and Nb show negligible reemission under typical sputtering conditions, Ta, W, and Pt show noticeable film deposition in regions obstructed from direct flux. TiW alloy sputtering shows evidence of the largest amount of reemitted flux. Sputtering conditions from 5 to 15 mT with power densities from 10 to 35 W/cm2 were studied, without significant change in the reemission flux. Variation of substrate temperature and moderate substrate bias was also not found to cause a measurable change in the reemission characteristics.
Growth of high-temperature NiTi1−xHfx shape memory alloy thin films by laser ablation of composite targets
Authors: Gu H. D. , Leung K. M. , Chung C. Y.
Published: July 2002

High-temperature NiTi1−xHfx shape memory alloy thin films with Hf contents up to 29.9 at. % were obtained by laser ablation of different composite targets. The crystal structures and phase transformation behavior of the annealed thin films were characterized by x-ray diffraction and differential scanning calorimeter, respectively. It is found that there are two phases (martensite and austenite) in the annealed thin films. The phase transformation temperatures increase from 31 to 175 °C for Mp and from 97 to 228 °C for Ap when the Hf content (x) increases from 13.4 to 29.9 at. %. Results are also compared with those of NiTi1−xHfx bulk alloys and thin films grown by other methods.
Optical properties and electron spectroscopy characterization of AlxTiyOz thin films
Authors: Yubero F. , Stabel A. , González-Elipe A. R.
Published: July 2002

Al x Ti y O z thin films (i.e., mixture of Al2O3 and TiO2) with different Al/Ti ratios have been characterized by several electron spectroscopies. The Auger parameter of Ti, determined by x-ray photoelectron spectroscopy, increases with the percentage of Ti in the films. The same trend is found for the evolution of the refractive index in the visible region n0, that, as measured by UV-Vis absorption spectroscopy, varies from 1.5 to 2.5 as a function of the percentage of Ti. Within the same range of compositions, the Auger parameter of Ti changes by 1.2 eV. Such behavior permits an empirical use of the Auger parameter to assess optical parameters of this type of films. On the other hand, reflection electron energy loss spectroscopy has provided information on the optical properties of the films in the far-ultraviolet region (5<ℏω<80 eV). From the analysis of the loss spectra, the refractive index n(ℏω), the extinction coefficient k(ℏω), and the absorption coefficient α(ℏω) have been obtained as a function of the energy ℏω. Differences in the magnitudes of these functions at given energies as well as in the elemental dipolar transitions have been found as a function of the composition of the thin films. Thus, for example, for an energy ℏω∼8 eV, the dependence of n(ℏω) on the titanium percentage is the opposite to that found in the visible region (ℏω=2.5 eV). The films show significant absorption [α(ℏω)≠0] for ℏω>5 eV, which produces a modulation in n(ℏω), that depends on the film composition. As a consequence, it is concluded that the correlation between the Auger parameter and the refractive index in the visible region does not hold when other energies are considered.
Cryogenic stabilization of high vapor pressure samples for surface analysis under ultrahigh vacuum conditions
Authors: Bruckner J. J. , Wozniak K. , Hardcastle S. , Sklyarov A. , Seal S. , Barr T. L.
Published: July 2002

A novel form of ultrahigh vacuum (UHV) cryogenic stabilization has been used to obtain high-resolution x-ray photoelectron spectroscopy (XPS) data from a complex amine, 1,8-bis(dimethylamino)naphthalene, whose solid phase exhibited at room temperature an unacceptably high rate of sublimation. Protonated versions of the amine exhibit hydrogen bonding. Electron spectroscopy for chemical analysis chemical shifts can be used to describe the strength and asymmetry of hydrogen bonding formed in proton sponge complexes. Analyzing the binding energy shifts of N (1s) induced by the presence of this hydrogen bonding required obtaining corresponding XPS spectra from the nonprotonated (reference) sample, but the reference sample sublimes under even moderate vacuum conditions. The combined results suggest that other high vapor pressure materials, particularly those that were previously considered to be too corrosive for routine analysis, can be cryogenically stabilized for surface analysis under similar UHV conditions.
Surface morphology of homoepitaxially grown (111), (001), and (110) diamond studied by low energy electron diffraction and reflection high-energy electron diffraction
Authors: Nishitani-Gamo Mikka , Loh Kian Ping , Sakaguchi Isao , Takami Tomohide , Kusunoki Isao , Ando Toshihiro
Published: July 2002

The surface morphology and crystallinity of homoepitaxially grown (111), (001), and (110) diamonds were comparatively investigated by using low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED). We found that the crystal quality and the surface smoothness of the homoepitaxial diamond on (111) strongly depends on the substrate temperature; the highest quality homoepitaxial diamond on (111) can be successfully grown at 690 °C. The highest quality homoepitaxial diamond had the smoothest C(111)-1×1 surface, which was evidenced by the first observation of sharp and clear Kikuchi patterns, comparable to those of a C(001) surface. Caution has to be exercised when judging the structure of a C(111) surface from a LEED(1×1) pattern, because its observation can encompass surface morphologies ranging from single-crystal to polycrystalline diamonds. In contrast, surface roughness has a dramatic effect on the RHEED diffraction pattern. In the smoothest C(001)-2×1/1×2 surface, the RHEED pattern shows spots rather than streaks. Growth on a (110) diamond surface results in {111}-oriented microfacets.
Mechanism of enhanced plasma transport of vacuum arc plasma through curved magnetic ducts
Authors: Zhang T. , Zeng Z. M. , Tian X. B. , Tang B. Y. , Chu P. K. , Brown I. G. , Zhang H. X.
Published: July 2002

The mechanism of the enhanced transport efficiency in a vacuum arc plasma source equipped with a curved magnetic filter is investigated. The relationship between the transported ion current and the cathodic arc current is determined, and our results suggest that the outer and inner walls of the duct interact with the plasma independently. The plasma flux is composed of two components: a diffusion flux in the transverse direction due to particle collisions, and a drift flux due to the ion inertia. The inner wall of the magnetic duct sees only the diffusion flux while the outer wall receives both fluxes. Thus, applying a positive potential to the outer duct wall reflects the ions and increases the output current. Our experimental data also show that biasing both sides of the duct is more effective than biasing the outer wall alone.
III-nitride dry etching: Comparison of inductively coupled plasma chemistries
Authors: Cho H. , Hahn Y.-B. , Hays D. C. , Abernathy C. R. , Donovan S. M. , MacKenzie J. D. , Pearton S. J. , Han J. , Shul R. J.
Published: July 2002

A systematic study of the etch characteristics of GaN, AlN, and InN has been performed with boron halide- (BI3 and BBr3) and interhalogen- (ICl and IBr) based inductively coupled plasmas. Maximum etch selectivities of ∼100:1 were achieved for InN over both GaN and AlN in the BI3 mixtures due to the relatively high volatility of the InIx etch products and the lower bond strength of InN. Maximum selectivities of ∼14 for InN over GaN and <25 for InN over AlN were obtained with ICl and IBr chemistries. The etched surface morphologies of GaN in these four mixtures are similar or better that those of the control sample.
Optical emission studies and neutral stream characterization of a surface reflection materials processing source
Authors: Tang Xianmin , Manos Dennis M.
Published: July 2002

We report optical emission studies of the plasma source and measurements using heat flux and momentum analyzers of the fast neutral flux and energy in a low-energy surface-reflection neutral source. Both optical emission and Langmuir probe studies indicate a mode transition from a capacitively coupled mode to an inductively coupled mode as the rf power is increased. Spectroscopic actinometry shows that the atomic species resulting from molecular dissociation increase with increasing rf power. Changing the reflector bias changes the neutral energy without changing the discharge composition. The measured heat flux and momentum carried by the fast neutrals are used to derive the flux-weighted average velocity and the particle flux of the neutral stream. The measured neutral stream energy is found to be 4–6 eV. The neutral flux increases with the rf power. The measured neutral energy increases less than linearly with the reflector bias. This might be caused by the decreasing reflection efficiency of the reflector plate or a large collisional loss as the neutrals traverse the process region. The etch rates and cleaning rates calculated from the measured neutral flux and previously reported measured ashing and cleaning rates are in good agreement.
Enhanced adhesion through local epitaxy of transition-metal nitride coatings on ferritic steel promoted by metal ion etching in a combined cathodic arc/unbalanced magnetron deposition system
Authors: Schönjahn C. , Donohue L. A. , Lewis D. B. , Münz W.-D. , Twesten R. D. , Petrov I.
Published: July 2002

In situ substrate cleaning by ion etching prior to deposition in physical vapor deposition processes is a key step in achieving good film adhesion, which is essential for all coating applications. Irradiation with metal or gas ions alters substrate surface chemistry, topography, and microstructure thus affecting subsequent film growth. This study compares Ti1−xAlxN/ferritic steel (x=0.54) interfaces formed after Cr ion bombardment at negative substrate biases, Us, ranging from 600 to 1200 V during a Cr cathodic arc discharge, stabilized with a 0.06 Pa Ar background pressure. Samples biased with −1200 V in an Ar glow discharge at a pressure of 0.6 Pa were also investigated. Microstructure and microchemistry of the interfaces was studied by scanning transmission electron microscopy with energy dispersive x-ray analysis using cross-sectional samples. Cr ion etching with Us=1200 V resulted in a net removal of over 100 nm of substrate material with the formation, through implantation, of a Cr-enriched near-surface region extending to a depth of ∼10 nm. As Us was reduced to 600 V, Cr accumulated at the surface as a ≳5 nm thick layer. Ar was incorporated at the surface to levels of 4–6 at. % during both Cr arc and Ar glow discharge etching. The microstructure of Ti1−xAlxN overlayers was dramatically affected by pretreatment procedures. Ar sputter cleaned steel surfaces (Us=1200 V) promote nucleation of randomly oriented grains leading to a competitive column growth with small column size and open boundaries. In contrast, Cr irradiation at the same bias voltage results in local epitaxial growth of Ti1−xAlxN on steel and lead to a superior performance in scratch testing compared to coatings deposited after Cr treatment with Us=600 V or Ar ion bombardment at Us=1200 V. Critical loads were 63, 47, and 27 N, respectively.
Polycrystalline silicon thin films with hydrofluoric acid permeability for underlying oxide etching and vacuum encapsulation
Authors: Kageyama Y. , Tsuchiya T. , Funabashi H. , Sakata J.
Published: July 2002

Specialized fabrication techniques created polycrystalline silicon (poly-Si) thin films that were permeable to a concentrated hydrofluoric acid (HF) solution, in order to support in situ vacuum encapsulation of surface microsensor devices on silicon wafers. 0.1-μm-thick poly-Si thin films were made permeable through processes of amorphous silicon film formation by low pressure chemical vapor deposition, successive postannealing for crystallization, and excessive phosphorus diffusion by a phosphorus oxichloride predeposition. Permeability was obtained both on borophosphosilicate glass and nondoped silica glass sacrificial layers. Porous microstructures at the silicon grain boundaries, which were induced by heavy doping of phosphorus and consequent segregation of soluble precipitates, were first observed using a secondary electron microscope and a field emission secondary electron microscope. These observations confirmed that the submicron pores permitted passage of the fluid to dissolve the underlying sacrificial oxide films. Vacuum encapsulation of shell structures covered with the permeable poly-Si thin film was also carried out to demonstrate the vibration of a gyroscope structure in the sealed shell.
Simulation and correction of geometric distortions in scanning Kelvin probe microscopy
Authors: Efimov Anton , Cohen Sidney R.
Published: July 2002

Capacitance due to geometric influence of the finite tip shape and influence of distant surface points can lead to artifacts in scanning Kelvin probe microscopy (SKPM) images. These artifacts appear as features in the SKPM image which are due only to tip/surface geometry and not to true surface potential variations. They can also cause blurring of real features. Such effects are most prominent for samples with rich topography. We present here a method for identifying and removing these artifacts, and demonstrate it for a gold sample with rich topography relative to the nearly flat surface potential fluctuations.
Design and fabrication of high transconductance modulation-doped (Al,Ga)As/GaAs FETs
Authors: Lee K. , Shur M. S. , Drummond T. J. , Su S. L. , Lyons W. G. , Fischer R. , Morkoç H.
Published: July 2002

Modulation-doped FETs grown by MBE exhibit very high currents and transconductances per unit gate width. In short gate FETs the high transconductances are a result of large electron velocities; typically 2×107 cm/s at 300 K and 3×107 cm/s at 77 K. Since the low field mobility does not strongly affect device performance, improvements were obtained by adjusting the parameters of the heterostructure to maximize charge transfer across the heterojunction. An improved calculation of the maximum charge transfer is used to derive closed expressions for the maximum current and transconductance. Predictions of increasing current and transconductance as the undoped (Al,Ga)As spacer layer thickness is decreased have been verified by experimental results. For a N-off FET with a 20 Å spacer layer transconductances as high as 250 mS/mm at 300 K and 400 mS/mm at 77 K have been obtained. Maximum currents as high as 200 and 300 mA/mm were obtained in N-off and N-on devices, respectively, at 300 K. In this paper the crystal growth, device fabrication, and design considerations for modulation-doped FETs are discussed.
Low pressure-MOCVD growth of Ga0.47In0.53As–InP heterojunction and superlattices
Authors: Razeghi M. , Duchemin J. P.
Published: July 2002

We report the latest results of a continuing study of low pressure-metal–organic chemical vapor deposition (LP-MOCVD) growth of InP and Ga0.47In0.53As–InP heterojunctions and superlattices, which describe the general growth of InP and GaInAs with specific application to quantum well heterostructure. A study of the sources and control of residual impurities in InP and Ga0.47In0.53As, the effects of source purity upon residual impurities, mobility, and 2 K PL intensity are detailed. Total impurity concentrations as low as 6×1014 cm−3 for InP and 3×1014 cm−3 for Ga0.47In0.53As have been obtained. Mobility as high as=μ (300)=5350, μ (77)=60 000 cm2 V−1 s−1 for InP, and μ (300)=12 000, μ (77)=60 000, μ (2)=100 000 cm2 V−1 s−1 for GaInAs layers have been measured.
An investigation of GaAs films grown by MBE at low substrate temperatures and growth rates
Authors: Metze G. M. , Calawa A. R. , Mavroides J. G.
Published: July 2002

We have achieved the first successful growth of GaAs films with good electrical properties at substrate temperatures below 480 °C. The electrical and photoluminescence properties of films grown at Ts≊380 and 450 °C have been dramatically improved by reducing the growth rate significantly below the usual rate of ∼1 μm/h. Reductions in the growth rate can be expected to improve the quality of MBE films by allowing sufficient time for Ga and As adatoms to jump to equilibrium lattice positions before they are incorporated into the growing crystal by interacting with other adatoms. We further observed that the density of a major morphological defect of MBE GaAs films—the oval defect—was strongly correlated with the growth rate. The density of such defects was ∼500 cm−2 for films grown at ∼0.02 μm/h.
Plasma potentials in supported discharges and their influence on the purity of sputter-deposited films
Authors: Ziemann P. , Koehler K. , Coburn J. W. , Kay E.
Published: July 2002

Ion energy distributions have been measured for supported dc Kr discharges (triode configuration) and the plasma potential Vp was determined as a function of the positive voltage applied to the support anode, the injected electron current, and the gas pressure. If Vp is larger than a typical energy threshold for sputtering Uth, sputtering of the chamber walls is a possible source of film contamination. Whereas in some dc-plasma configurations as commonly used, Uth will not be exceeded, it will be shown that in supported dc discharges sputtering from grounded surfaces can be a significant source of film contamination. This has been experimentally confirmed by determining the Fe concentration within sputter-deposited Pd films for the two cases Vp >Uth and Vp <Uth by SIMS analysis and the temperature dependence of the magnetic susceptibility.
Distribution of nitrogen in thermally nitrided SiO2
Authors: Yoriume Yutaka
Published: July 2002

Thermally oxidized SiO2 films on silicon wafers were directly thermally nitrided by heating in an anhydrous ammonia gas ambient. The nitrided film was studied by Auger electron spectroscopy, infrared spectroscopy, and etching rate measurements. It was found by AES measurement that nitrogen permeates through SiO2 films even as thick as 1000 Å, if nitrided at 900 to 1100 °C, and that it distributes throughout the film. At the silicon interface, a nitrogen pileup was observed. Results of infrared spectroscopy and etching rate measurements confirmed the AES measurements.
Doping and transport studies in InxGa1−xAs/GaAs strained-layer superlattices
Authors: Fritz I. J. , Dawson L. R. , Zipperian T. E.
Published: July 2002

High quality InxGa1−xAs/GaAs strained-layer superlattices (SLS’s), with 0.11≤x≤0.20, have been grown by molecular beam epitaxy. The test structures grown include the first doped material in this SLS system, with Si being used for n-type doping and Be for p-type. A number of structures with up to 80 superlattice periods and with layer thicknesses in the 40–140 Å range have been characterized by x-ray diffraction and optical techniques. Doped specimens have been characterized by C–V profiling and, for diode structures, by I–V, four-terminal resistivity, and Hall-effect measurements. Hall mobilities (parallel to the layers) at 23 °C are comparable to those of high quality bulk alloy material, further evidence of the high crystalline quality possible in multilayer structures with thin, highly mismatched (>1%) layers.
Transport characteristics of L-point and Γ-point electrons through GaAs–Ga1−xAlxAs–GaAs(111) double heterojunctions
Authors: Mailhiot C. , Smith D. L. , McGill T. C.
Published: July 2002

We present here a study on the transport characteristics of L-point and Γ-point derived electrons through abrupt GaAs–Ga1−xAlxAs–GaAs(111) double heterojunctions. The use of complex-k band structures in the tight-binding approximation and transfer matrices provide a reasonably accurate description of the wave function at the GaAs–Ga1−xAlxAs interface. A representation of the wave function in terms of bulk complex-k Bloch states is used in the GaAs regions where the potential is bulklike. A representation of the wave function in terms of planar orbitals is used in the central Ga1−xAlxAs region where the potential deviates from its bulk value (i.e., interfacial region). Within this theoretical framework, realistic band structure effects are taken into account and no artificial rules regarding the connection of the wave function across the interface are introduced. The ten-band tight-binding model includes admixture in the total wave function of states derived from different extrema of the GaAs conduction band. States derived from the same extremum of the conduction band appear to couple strongly to each other, whereas states derived from different extrema are found to couple weakly. Transport characteristics of incoming L-point and Γ-point Bloch states are examined as a function of the energy of the incoming state, thickness of the Ga1−xAlxAs barrier, and alloy composition x. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating depending on the nature of the Bloch states available for strong coupling in the alloy. Since Bloch states derived from different extrema of the conduction band appear to couple weakly to each other, it seems possible to reflect the low velocity L-point component of the current while transmitting the high velocity Γ-point component.
Optical investigation of MQW system InP–InGaAs–InP
Authors: Kodama K. , Ozeki M. , Komeno J.
Published: July 2002

A new multiquantum well system, InP–InGaAs–InP, has been grown by the chloride transport vapor phase epitaxy. The Auger measurements show that a very sharp InGaAs–InP heterointerface (less than 30 Å) can be obtained by the present growth system. Optical absorption and photoluminescence measurements give the evidence for the formation of the quantum wells in InGaAs layers. Temperature dependence of photoluminescence indicates that the dominant emission at low temperatures is interpreted as the band-to-acceptor transition. It also shows that temperature dependence of the transition energy from hole subband to electron subband is apparently affected by the thickness of the quantum well. Two models are presented for this. One takes into account the localized phonons in the InGaAs–InP heterointerface region whose frequency is higher than that in the bulk samples. The other considers the difference in the thermal expansion coefficients of InGaAs and InP, which reduces a shift of the [000] conduction band minimum of the InGaAs quantum well layer toward higher energy with decreasing temperature.
Time and temperature dependences of phosphorus evolution from InP
Authors: Van Uitert L. G. , Gallagher P. K. , Singh S. , Zydzik G. J.
Published: July 2002

Indium phosphide decomposes evolving phosphorus at temperatures below 360 °C in vacuum. Hence, heating in this range during processing epitaxial InGaAs films on InP substrates may lead to surface contamination of the active layer by phosphorus. This contamination can be minimized at elevated temperatures by initially depositing a passivating layer over the exposed parts of the substrate and/or active film well below the decomposition range of the substrate (e.g., at 250 °C) and then sintering the film directly or while continuing deposition at a higher temperature. The vapor pressure of phosphorus evolved from InP increases by an order of magnitude for each 45 °C increase in temperature.
Multilayer resist technique for submicron optical lithography
Authors: Ting C. H. , Liauw K. L.
Published: July 2002

Analysis has shown that the limiting factor in achieving 1 μ technology in optical lithography is mainly due to nonideal operating conditions such as surface topography, reflectivity, defocusing, etc. By using a multilayer resist process to eliminate these extraneous factors, we have demonstrated that optical lithography can be pushed beyond 1 μ into the submicron range. The advantages and problems encountered with the bilayer DUV flood exposure process were pointed out. One of the most serious problems, due to reflected light from surface topography, was corrected by using an antireflecting coating between the PMMA and AZ resist layers. This antireflection coating layer also eliminates the interface mixing between PMMA and AZ resists. A trilayer resist process was developed based on the highly directional RIE process. A new barrier film based on spin-on-glass was optimized to obtain defect free films. This spin-on barrier layer greatly simplifies the work flow and provides significant cost savings over the conventional vacuum deposited or CVD films. Submicron resolution capability and good dimension controls over severe wafer surface topography have been demonstrated. The trilayer resist process has been demonstrated to be capable of handling dimensions beyond the resolving power of currently available optical lithographic systems.
Resist exposure with light ions
Authors: Adesida I. , Anderson C. , Wolf E. D.
Published: July 2002

Radiation yields or Gs-values in polymethylmethacrylate (PMMA), which are the number of chain scissions per 100 eV of absorbed energy, due to irradiation with electrons, protons, and helium, lithium, beryllium, and boron ions have been measured. Gs values for protons and electrons are the same at ∼0.75, while those of helium, lithium, beryllium, and boron ions are 0.45, 0.44, 0.40, and 0.45, respectively. Initial results on sensitivities and mean pathlengths of ions in PMMA obtained from solubility studies are also presented.
Role of arsenic (As2, As) in controlling the quality of GaAs grown by MBE: Theoretical studies
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

We report results of theoretical investigations to understand the atomistic mechanisms responsible for controlling the surface roughness and concentration of native point defects in MBE grown GaAs. We have simulated growth of GaAs using both As2 and As as the sources of anions in the vapor phase using Monte Carlo techniques. In the case of As2 as a source, we have examined several possible reaction pathways for the dissociative chemisorption of As2 and their influence on the quality of the grown system (under anion overpressure). Different reaction pathways introduce different constraints for the incorporation of atoms from the vapors. These simulations indicate that lowering the constraints for As2 chemisorption decreases the defect nucleation site concentration but leads to a rougher growth front profile. We also report results of studies on GaAs growth using monatomic As as a source. The mechanisms responsible for As and As2 incorporation are expected to be very different and our model studies show important differences in the quality of the material grown. We have also examined the effect of varying the ratio of Ga to As vapor pressure on GaAs growth using monatomic As as a source and find that it has an important role in controlling the quality of the growth front profile.
Interfacial constraints on device performance
Authors: Lile D. L.
Published: July 2002

Electronic devices can be significantly affected in their behavior by the properties of the surfaces and interfaces which delineate their structure. Unfortunately, such surface effects are often degrading, acting to reduce the performance of the device below that to be expected in the ideal case. This paper will attempt to review these processes and relate them to what is known about the properties and structures of surfaces. In particular those deficiencies which most severely impact device performance will be identified, and suggestions made as to where improvements in understanding of surface control might have the greatest impact on resulting device development.
Influence of interfacial structure on the electronic properties of SiO2/InP MISFET’s
Authors: Geib K. M. , Goodnick S. M. , Lin D. Y. , Gann R. G. , Wilmsen C. W. , Wager J. F.
Published: July 2002

In order to make a viable InP MISFET technology, two major problems remain to be solved: (1) instability in the channel current and (2) variations in the channel mobility with processing. These problems are strongly affected by the chemical and physical structure of the semiconductor/insulator interface. This paper presents results of an investigation of the deposited SiO2/InP interface using XPS, UPS, and ELS combined with transport measurements on special Hall geometry MISFET’s. Physical studies of the SiO2/InP interface using XPS show the presence of a 20–40 Å thick native oxide layer primarily composed of InPO4 next to the InP and In2O3 close to the SiO2. UPS and ELS data suggests that the In2O3 forms a trap level slightly above the conduction band. The variation of the channel mobility with surface field and temperature imply that for these devices, the channel mobility is completely dominated by scattering from interface charges and surface roughness, with only a small contribution arising from the bulk optical phonon.
New approach to the k⋅ p theory of semiconductor superlattices
Authors: Mailhiot C. , McGill T. C. , Smith D. L.
Published: July 2002

Along with the growing interest in semiconductor superlattices, various theoretical schemes have been proposed to study the nature of the electronic states within these structures. The work presented here highlights a new method to investigate the electronic and optical properties of semiconductor superlattices. The backbone of the theory rests on a realistic description of the complex-k band structure of the constituent semiconductors coupled with a suitable set of boundary conditions for the superlattice wave function. The bulk Bloch solutions, propagating and evanescent, in each semiconductor are described within a full-zone k ⋅ p Hamiltonian that provides an accurate description of the solutions up to the first Brillouin zone edge. An attractive feature of the present treatment is that the complex-k bulk Bloch solutions of each constituent semiconductor are expanded on the same set of zone-center basis functions. A new technique for constructing the k ⋅ p Hamiltonian of each constituent semiconductor is presented. The superlattice wave function is described by a linear combination of propagating and evanescent bulk Bloch solutions. The expansion amplitudes are determined by imposing a set of boundary conditions on the superlattice wave function across the superlattice interfaces. These boundary conditions are used to formulate an eigenvalue problem whose solution yields directly the corresponding superlattice states associated with real or complex superlattice wave vector q. This method provides an accurate technique to treat superlattices where one of the constituent semiconductors has an indirect energy band gap. An exposition of the formalism is presented, and the physical origin of the superlattice states is studied. The test case of the GaAs–AlAs (100) superlattice is presented. Pertinent applications are also discussed.
Barrier control and measurements: Abrupt semiconductor heterojunctions
Authors: Kroemer Herbert
Published: July 2002

A brief critical review is given of diverse techniques used to measure heterojunction band lineups; they range from very reliable to worthless. Another problem pertains to the heterosystems themselves: Data on systems in which two semiconductors from a different pair of columns of the periodic table are combined, should be reviewed with suspicion, although some selected pairs are probably trustworthy—but none in which a compound semiconductor was grown on an elemental one. Technologies that do not lead to device-quality interfaces also probably do not yield device-quality lineup data. A list of the most trustworthy experimental data is given. The simplest possible theoretical framework for a theory of band lineups is a model of linear superpositon of atomiclike bulk potentials. Such a model automatically leads to a theory that is linear and transitive, in which the band lineups are orientation independent, and in which a technology dependence of the band lineups requires a technology-dependent deviation of the atomic arrangement from the ideal one. The Harrison theory is both the simplest and the most successful theory of band lineups, although it still does not meet the needs of the device physicist. The set of most reliable data selected earlier agree very well with this theory, with a largest deviation of 0.18 eV and a standard deviation of 0.13 eV.