bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of boron effects on the reaction of Co and Si1−xGex at various temperatures
Authors: Huang H. J. , Chen K. M. , Chang C. Y. , Huang T. Y. , Chang T. C. , Chen L. P. , Huang G. W.
Published: July 2002

The effects of boron on Co and Si1−xGex interfacial reaction were studied. Undoped and in situ boron-doped strained Si0.91Ge0.09 and Si0.86Ge0.14 layers prepared at 550 °C by an ultrahigh vacuum chemical vapor deposition system were subjected to Co silicidation at various rapid thermal annealing (RTA) temperatures ranging from 500 to 1000 °C. The resulting films were characterized by a sheet resistance measurement, Auger electron spectroscopy, x-ray diffractometry (XRD), high resolution x-ray diffractometry, secondary ion mass spectroscopy, scanning electron microscopy, and transmission electron microscopy. Seen from XRD spectroscopy, a Co(Si1−yGey) cubic structure was formed with RTAs ranging from 500 to 700 °C. For boron-doped samples, the CoGe fraction in Co(Si1−yGey) was less than that in undoped samples, indicating that boron atoms retarded the incorporation of Ge into the Co(Si1−yGey) ternary phase. It also led to a large Ge pileup at the interface between the Co-rich and silicidation regions. On the other hand, from the high resolution x-ray spectra, the presence of boron led to less relaxation of the strained Si1−xGex lattice. It is the first time that small boron atoms inhibiting the relaxation of the Si1−xGex layer during silicidation was observed. Furthermore, from the sheet resistance measurement, the formation of CoSi2 was found to be slightly retarded in boron-doped samples, due probably to the decrease of Co or Si diffusivities as a result of boron accumulation at the Co/SiGe reaction interface. At temperatures above 800 °C, CoSi2 formed and Ge segregated to the silicide boundaries and the upper reaction region was discovered. These phenomena caused by B dopants are explained in detail.
On the possibility of MBE growth interface modification by hydrogen
Authors: Bachrach R. Z. , Bringans R. D.
Published: July 2002

The study of the clean surface reconstructions of GaAs(100) and (1̄1̄1̄) has been extended with an investigation of their interaction with atomic and molecular hydrogen. This is of interest both because hydrogen is a common growth ambient and because there is some indication that growing in the presence of hydrogen improves crystal electrical quality. The core level photoemission spectroscopy results show that at a saturation hydrogen coverage, the atomic hydrogen converts the clean surface reconstructions to a distinct semiconducting reconstruction with a specific composition independent of the starting surface reconstruction. A mechanism is deduced whereby the hydrogen forms surface arsenic and gallium hydrides which sublime. These results indicate that hydrogen could modify the MBE growth interface by regulating the surface gallium to arsenic ratio.
Photoemission study of GeAs(2̄01): A model for the As-stabilized Ge surface on GaAs/Ge heterojunctions
Authors: Stucki F. , Lapeyre G. J. , Bauer Robert S. , Zurcher P. , Mikkelsen J. C.
Published: July 2002

We present a study of the electronic states of GeAs as a model for the ordered, anion-stabilized surface phases which form on Ge when it is grown epitaxially on GaAs substrates using MBE. Angle-resolved, normal emission photoelectron energy distribution curves for four different azimuthal orientations of the GeAs(2̄01) face (i.e., four different polarizations) have been measured using photon energies from hν=10 to 28 eV. The valence band structure plots (binding energy versus photon energy) show behavior typical of a layered compound. A large number of valence band states (about 12) are observed, and they show essentially no hν dispersion in normal emission and very little dispersion with polar angle. The electronic states are therefore localized both within and normal to the layer. The excitation of the Ge 3d and the As 3d core levels into conduction band states observed by measuring the core hole decay emission does not show any enhancement peaks as usually observed if empty surface states exist in the conduction band. This suggests that the GeAs(2̄01) surface may not have any surface states. Chemical bonding information was obtained by measuring the Ge 3d core level binding energy. The Ge is more tightly bound compared to the bulk Ge as indicated by a 3d core level chemical shift of 0.45±0.1 eV toward higher binding energy. 3d core threshold emission for both the Ge and the As is used together with the line shape of the valence band edge emission to determine a forbidden band gap is 0.4±0.3 eV. These results support the Bauer/Mikkelsen hypothesis that the Ge:As surface phase that floats on top of the MBE GaAs/Ge heterojunction is energetically more favorable than the corresponding clean Ge surface having unsatisfied dangling bonds. The data on GeAs(2̄01) leads to a picture of an As-terminated surface having highly directional oribtals and very low reactivity.
Diffraction effects on pattern replication with synchrotron radiation
Authors: Atoda N. , Kawakatsu H. , Tanino H. , Ichimura S. , Hirata M. , Hoh K.
Published: July 2002

With synchrotron radiation from the storage ring ETL–TERAS, the influence of Fresnel diffraction on replicated patterns was investigated. Spatial intensity distributions due to the diffraction were calculated with Fresnel integrals and compared with replicated patterns. Pattern degradation due to the diffraction depends on a parameter UO=W/(Gpλ/2)1/2, where W is the pattern width, Gp the mask-to-wafer distance, and λ the wavelength. From the calculation and the experiments it is concluded that the value of U0 is needed to be larger than about three for a satisfactory pattern replication. Work with an experimental stencil mask with patterns of submicron dimensions is also described briefly.
The use of substrate annealing as a gettering technique prior to molecular beam epitaxial growth
Authors: Palmateer S. C. , Eastman L. F. , Calawa A. R.
Published: July 2002

Thermally stable GaAs substrates are needed for ion implantation and active layer growth for the fabrication of microwave devices and integrated circuits. The outdiffusion and redistribution of impurities and related deep levels from GaAs substrates during molecular beam epitaxial (MBE) growth is shown to affect interface quality and device performance. The present paper supports substrate annealing and repolishing as an impurity gettering technique prior to epitaxial growth to reduce interface and surface accumulation of unintentional substrate related impurities. The accumulation of impurities at the surface of GaAs substrates after prolonged annealing is identified by photoluminescence. Epitaxial layers grown on annealed substrates have reduced interface and surface accumulation of substrate related impurities as identified by secondary ion mass spectroscopy and capacitance–voltage profiling. The reduction of these substrate related impurities is observed to be important in the growth of homojunctions and heterojunctions by MBE.
Computer simulations of surfaces, interfaces, and physisorbed films
Authors: Abraham Farid F.
Published: July 2002

We survey selected computer simulations or ‘‘experiments’’ relating to the statistical physics of surface phenomena. An introduction to the Monte Carlo and molecular dynamics simulation techniques is presented, followed by chosen computer simulation applications which have been done mainly at the IBM Research Laboratory over the last several years. The examples are taken from studies of the structure and thermodynamics of microclusters, liquid–vapor and liquid–solid interfaces and quasi-two-dimensional physisorbed films. An up-to-date bibliography of the various topics is given at the conclusion.
Impurities in refractory metals/silicides
Authors: Liang S. C.
Published: July 2002

For the purpose of searching information on the desired purity specification optimum of refractory metal/silicide materials to be used by the IC manufacturer, the views of a material supplier are presented. In particular, ‘‘high purity’’ does not necessarily mean high quality, because all impurities are not equal. Samples of materials representing currently achievable production technology have been collected and analyzed (principally by spark-source mass-spectrometry). Impurities are grouped into three categories, the known sensitive elements (alkalis and α emitters particularly uranium/thorium), the major impurities (mostly the 4th period transition elements) which define the overall purity, and other impurities in lesser concentrations with ill-defined effects on material usefulness. The uranium content as a source of soft error is discussed in some detail. A specification for refractory metals/silicides for VLSI application is proposed for industry consideration.
Laser-induced selective deposition of micron-size structures on silicon
Authors: Liu Y. S. , Yakymyshyn C. P. , Philipp H. R. , Cole H. S. , Levinson L. M.
Published: July 2002

The feasibility of high speed direct writing of high resolution structures using a laser beam was demonstrated. Tungsten was selectively deposited on silicon via surface reduction reaction of tungsten hexafluoride. Fine lines of micron dimension with smooth surface morphology were fabricated using an argon laser at a writing speed of several cm per second. Compositions and structures of the micron-size lines, characterized using various microprobe analysis techniques including scanning Auger microprobe, Raman microprobe, and Rutherford microion-beam spectroscopy, are discussed.
Use of TiSi2 to form metal–oxide–silicon field effect transistors with self-aligned source/drain and gate electrode
Authors: Yachi T. , Suyama S.
Published: July 2002

A new TiSi2 self-alignment formation in the source/drain region and gate electrode, which realizes a high performance metal–oxide–silicon field effect transistor (MOSFET) with a low-resistance interconnect, is described. The self-alignment formation utilizes Ti-silicide deposition and its subsequent oxidation, leading to a TiSi2/poly-Si gate isolated from the TiSi2/n+- and p+-diffusion source/drain in p-well CMOS devices. A sheet resistance of about 1.5 Ω/sq on TiSi2/n+- and p+-diffusion and 4 Ω/sq on the TiSi2/poly-Si gate have been achieved. Contact resistance between the TiSi2 layer and Al wire was also 0.08 μΩ cm2. MOSFET characteristics with the TiSi2 layer are for the most part similar to those of poly-Si gates.
Ionization potentials, electron affinities, and band offsets
Authors: Van Vechten J. A.
Published: July 2002

In hopes of relieving some of the confusion regarding band offsets at semiconductor heterojunctions, the problem is addressed from a simple, fundamental thermodynamics point of view. It is noted that one form of an ‘‘electron affinity rule’’ can be stated which is exact and rigorous, but not very useful. A modified form of the electron affinity rule, in which the effect of electrostatic fields at the surface are to be excluded from experiment or not calculated from theory, can be stated which is almost rigorous and generally useful.
A Raman scattering study of GexSi1−x/Si strained-layer superlattices
Authors: Cerdeira F. , Pinczuk A. , Bean J. C. , Batlogg B. , Wilson B. A.
Published: July 2002

The Raman spectrum from GexSi1−x/Si strained-layer superlattices is critically compared to that from commensurate and incommensurate single layers of the same composition. Our results confirm that the lattice mismatch in commensurate single layers and superlattices is entirely accommodated by a homogeneous tetragonal compression of the alloy layers. The technique is also used to measure absorption coefficients in single layers of GexSi1−x. We studied the Raman cross section of the three alloy peaks as a function of incident laser frequency in the interval 1.8 eV<ℏωL<2.7 eV. The relative cross section (alloy/Si) for superlattice samples exhibits a single peak at a value of ℏωL which lies between the energies of the E1 and E1+Δ1 optical transitions of bulk material for the same composition.
Ion-beam-assisted etching of diamond
Authors: Efremow N. N. , Geis M. W. , Flanders D. C. , Lincoln G. A. , Economou N. P.
Published: July 2002

The high thermal conductivity, low rf loss, and inertness of diamond make it useful in traveling wave tubes operating in excess of 500 GHz. Such use requires the controlled etching of type IIA diamond to produce grating like structures tens of micrometers deep. Previous work on reactive ion etching with O2 gave etching rates on the order of 20 nm/min and poor etch selectivity between the masking material (Ni or Cr) and the diamond. We report on an alternative approach which uses a Xe+ beam and a reactive gas flux of NO2 in an ion-beam-assisted etching system. An etching rate of 200 nm/min was obtained with an etching rate ratio of 20 between the diamond and an aluminum mask.
Ion beam lithography at nanometer dimensions
Authors: Adesida I. , Kratschmer E. , Wolf E. D. , Muray A. , Isaacson M.
Published: July 2002

Factors affecting the ultimate resolution of ion beam lithography are discussed. These factors are primary ion scattering, recoil atom scattering, range of secondary electrons, and resist properties (i.e., resist sensitivity and molecule size in the resist). From a consideration of these factors, it is estimated that minimum linewidths of ≲10 nm can be achieved in polymethyl methacrylate (PMMA) using light ions. For heavy ions such as gallium, the resolution limit is estimated to be ∼30 nm with the limitation being due to recoil atom scattering. Fabrication of high resolution silicon nitride stencil masks is described and replication of the masks with protons in PMMA is demonstrated with features as small as 20 nm.
Segregated AlGaAs(110) grown by molecular beam epitaxy
Authors: Wang W. I. , Kuan T. S. , Tsang J. C. , Chang L. L. , Esaki L.
Published: July 2002

We have found that AlGaAs films grown by molecular beam epitaxy on (110) orientation tend to segregate to their constituent binaries on an extremely fine scale. However, the microscopic segregation in AlGaAs does not impede its capability of providing suitable, macroscopic barriers in the formation of heterostructures. High mobility two-dimensional electrons and holes in modulation-doped AlGaAs/GaAs(110) heterojunctions are demonstrated for the first time, with obvious implications for the combined growth of IV and III–V materials.
Properties of dc magnetron reactively sputtered TiN
Authors: Stimmell Jim
Published: July 2002

Titanium nitride is of interest for IC fabrication because of its excellent performance as a metallic diffusion barrier. TiN films have been deposited in a batch sputtering system equipped with dc magnetron cathodes, rf substrate bias, and independently controlled Ar and N2 sources. A threshold value of N2 flow exists, above which nitridation of the Ti target face is believed to occur. Operation above this threshold results in lower deposition rate and higher cathode voltage. It is demonstrated that high quality films can be deposited at N2 flows below the target nitridation threshold, resulting in an approximate threefold improvement in deposition rate. As-deposited films on (100) silicon have resistivities of 50–60 μΩ cm and moderate compressive stress. rf substrate bias is required to achieve these resistivities; excess bias increases compressive stress. RBS profiles of deposited films show low levels of oxygen contamination and nominally stoichiometric films over a considerable range of deposition conditions. The films can be dry etched using conventional aluminum etch equipment and chemistries. The resulting etch profiles are anisotropic with no tendency to undercut. Films deposited under these conditions also have the potential of reducing particulate generation, since the deposits which accumulate on unbiased shielding within the deposition chamber are Ti, rather than the more brittle and compressively stressed TiN.
Reflection high-energy electron diffraction study of the growth of In on GaAs(110) at different temperatures
Authors: Savage D. E. , Lagally M. G.
Published: July 2002

Measurements have been made of the growth of In on GaAs(110) at two temperatures using reflection high-energy electron diffraction (RHEED). Growth occurs by 3D island formation. Island orientations, sizes, volumes, separations, and densities are extracted from the angular profiles of transmission diffraction beams from the In. The dose and temperature dependencies of these quantities are investigated. The growth microstructure is related to concepts of barrier formation. It is suggested that Fermi level pinning measurements in this system depend on band bending in the substrate laterally away from the edges of the island that are separated by the bare substrate.
Determination of band offsets in AlGaAs/GaAs and InGaAs/GaAs multiple quantum wells
Authors: Ji G. , Huang D. , Reddy U. K. , Unlu H. , Henderson T. S. , Morkoç H.
Published: July 2002

The determination of valence band offsets Qv by fitting the optical transmission spectra for AlxGa1−xAs/GaAs and InyGa1−yAs/GaAs multiple quantum wells (MQWs) is discussed. The valence band offset Qv is defined as Qv =ΔEv/(ΔEv+ΔEc), where ΔEv and ΔEc are the valence and conduction band discontinuities at the heterojunction. For AlxGa1−xAs/GaAs (Type I for both heavy holes and light holes, i.e., electrons, heavy holes, and light holes are located in the same layers) the energy separation ΔE between the first light and heavy hole subbands in the valence band is used to determine the valence-band offset Qv. In order to improve the precision, MQWs with narrow well widths and higher Al mole fraction x should be used. Further, the inclusion of coupling between the valence and conduction subbands in Kane’s three-band model is also essential. However, Qv is still not determined uniquely by the above energy difference ΔE. Different combinations of Qv and heavy hole effective masses mhh in GaAs can lead to the same ΔE. The forbidden transition E13h in a narrow well can be used to identify the actual values of mhh and Qv. [The designation Enmh(l) refers to the energy separation of the nth conduction subband and mth heavy (light) hole subband.] Following such a procedure, we find that Qv =0.33 and mhh =0.34 m0 for AlxGa1−xAs/GaAs MQWs (x<0.37). For InyGa1−yAs MQWs (Type I for heavy holes and Type II for light holes, i.e., both electrons and heavy holes are located in the same layers, but the light holes are in different layers), the transition energies between the conduction subbands and the light hole valence subbands are much better parameters to determine the band offsets in comparison with the transitions involving the heavy holes. Both the optical measurements and the calculations including the strain effect show that E11l between

the first conduction subband and the first light hole valence subband in the MQWs with wider well widths is a sensitive enough parameter to determine the band offsets. By comparing with the optical measurements we obtained Qvh =0.30 and Qvl =−0.23 (Type II) (for 0.13<y<0.19) for the heavy hole and light hole valence band offsets, respectively.
Schottky barrier formation of various metals on n-GaAs (100) by electrochemical deposition
Authors: Allongue P. , Souteyrand E.
Published: July 2002

Electrochemistry is used to deposit various metals (Pt, Pd, Ni, Co) on n-GaAs (100) surfaces to form Schottky barriers. For the first time very good rectifying characteristics, with an ideality factor n=1.04–1.08, are obtained, while the barrier heights match quite well those made under ultrahigh vacuum conditions. It is also shown that the possible disadvantages of this wet technique (oxidation, contamination,...), can be overcome provided that the conditions of deposition are carefully looked after: strong correlations between the electrical characteristics (studied by I–V and C–V measurements) and the interfacial morphology and composition (studied by Rutherford backscattering, nuclear reaction observation, and transmission electron microscopy) are evidenced when the electrodeposition conditions are varied for a given metal. The advantages of the method are also discussed within the framework of our results.
Ion species dependence of focused-ion-beam lithography
Authors: Matsui Shinji , Mori Katsumi , Shiokawa Takao , Toyoda Koichi , Namba Susumu
Published: July 2002

The dependence of the ion-beam lithographic characteristics of both poly(methylmethacrylate) (PMMA) positive resist and chloromethylated polystyrene (CMS) negative resist for different ions has been studied using a Au–Si–Be source. Demonstrated have been 50 nm lines in 300-nm-thick CMS using 200-keV-Be++ions. The resist sensitivity increases with decreasing ion range, i.e., Au+>Au++>Si+>Si++>Be+>Be++, and focused-ion-beam (FIB) resist sensitivity is 10–100 times larger than that for 20-kV-electron beam. Moreover, lines written in both resists become discontinuous at low dose for both Si and Be ions, which may be caused by shot noise or by a jet-like protrusion on the end of the Taylor cone shape of the ion source.
Formation of misfit and threading dislocations in molecular-beam epitaxy grown strained layer epitaxy: Role of growth modes
Authors: Singh Jasprit , Bajaj K. K. , Dudley S.
Published: July 2002

The dislocation-formation process during growth from vapor is studied for one and two-dimensional monolayer overgrowth using a continuous space Monte Carlo approach. This process is found to be quite sensitive to the sequence of addition of the atoms of the strained material from the vapor. In particular, for the strained overlayer we find that if atoms are added at step edges (i.e., if atomic surface migration is high) misfit dislocations are produced which retain the underlying substrate epitaxy. However, a random addition of atoms is found to produce slip dislocations which destroy the underlying epitaxy. The strain energy buildup in the overlayer is also studied as a function of coverage.
Band offsets at interfaces between HgTe, CdTe, and InSb
Authors: Van de Walle Chris G. , Martin Richard M.
Published: July 2002

We have performed self-consistent density-functional calculations in order to determine the electronic structure and band offsets at ideal (110) interfaces between HgTe, CdTe, and InSb. These materials are very nearly lattice matched; strains due to the small lattice mismatch have negligible effects on the lineups. Local-density-functional theory, together with ab initio pseudopotentials, is used to calculate charge densities and potentials for the interface system; this allows us to determine the lineup of the bulk band structures. The following valence-band discontinuities are derived: 0.27 eV for CdTe/HgTe, 0.91 eV for HgTe/InSb, and 1.19 eV for CdTe/InSb. These values obey the transitivity rule. For HgTe/CdTe, we also examined the (100) and (111) interface orientations; the valence-band offset is the same in all cases. We have also used our simpler ‘‘model solid’’ approach to predict the lineups; the results are in very good agreement with those from the self-consistent interface calculations. Noticeable differences are found, however, with values obtained from model theories by Tersoff and by Harrison. Our value for HgTe/CdTe also clearly differs from ΔEv≊0, predicted by the common anion rule. Results for alloys can be obtained by interpolating our results for ΔEv for the pure materials. We discuss how changing the alloy composition x in HgxCd1−xTe/InSb interfaces can result in varying the band offsets over a wide range of values. Finally, we present a discussion of the experimental values that have been reported for HgTe/CdTe, and find good agreement between our theoretical value and the experimental result obtained from photoemission data.
Core electron binding energy shifts and screening in tetrahedral semiconductors
Authors: Klepeis John E. , Harrison Walter A.
Published: July 2002

Tight-binding heterojunction band offset calculations are brought into conceptual agreement with natural band lineup models by redefining the average hybrid energy to be the common reference level in each semiconductor. The self-consistent calculation of charge redistribution in semiconductor bonds in the presence of a substitutional impurity, using tight-binding theory based upon universal parameters with the inclusion of coulomb interactions, is extended to include the case of polar semiconductors. The core-to-valence-band maximum binding energy shifts in semiconductor alloys are then obtained using the results of this calculation. It is found that, in general, these shifts do not coincide with heterojunction band offsets as would be suggested by a natural band lineup approach. Differences in the two values occur as a result of lattice mismatch and/or a disparity in the hybrid energies. However, in the case of the cadmium telluride/mercury telluride and aluminum arsenide/gallium arsenide systems, where the mismatches and hybrid energy differences are small, the two values are found to be nearly the same, in agreement with experiment. These results suggest a limited applicability of models which neglect charge redistribution.
Thermal stability of the anodic oxide/Hg1−xCdxTe interface
Authors: Stahle C. M. , Helms C. R. , Simmons A.
Published: July 2002

We have studied the stability of the anodic oxide/Hg1−xCdxTe interface upon annealing with the aid of electrical capacitance–voltage (C–V) measurements, the thermodynamic properties of the Hg–Cd–Te–O system, and Auger sputter profiles. The C–V measurements on metal–insulator–semiconductor (MIS) devices showed a large increase in the positive fixed charge and slow interface traps as well as a conversion from p type to n type upon annealing at 100 °C. The equilibrium phase diagram predicted that any oxide containing Hg and a Te:Cd>1 at the interface will be unstable and react with the Hg1−xCdxTe substrate to form HgTe, Hg, Te, as well as lower x value Hg1−xCdxTe with subsequent degradation of electrical device characteristics. The Auger sputter profiles of thermally stressed oxide films (170 to 220 °C) gave support for these interface reactions with measurements of an enhanced Cd layer (∼150 Å) in the oxide and an enhanced Hg and depleted Cd layer (∼240 Å) in the substrate near the interface.
Asymmetric interface roughness in semiconductors grown by molecular-beam epitaxy
Authors: Dudley Scott , Singh Jasprit , Bajaj K. K.
Published: July 2002

Computer simulations of crystal growth by molecular-beam epitaxy (MBE) are used to study the nature of surface (interface) roughness as the crystal is being grown. The simulations were done on a Cray X-MP computer using a 100×100 atom substrate. The results presented use parameters for gallium arsenide but can be generalized to other systems. The nature of the surface is presented in terms of three quantities: (1) reflection high-energy electron diffraction (RHEED) intensity; (2) step density, and (3) island size distribution; all of which are calculated directly from the simulated crystal and expressed as a function of growth time. The RHEED intensity is evaluated, within the kinematical approximation, for the ‘‘off-Bragg’’ specular condition using the surface atoms only. The step density is the number of monolayer steps (up or down) that a tiny man would take as he walked along the surface in either the (110) or (11̄0) direction. This quantity is normalized and evaluated along both directions on the surface as a function of time. It is in the step density that asymmetry of the order of 30% can be seen. The cause of the aforementioned asymmetry is shown to be due to anion incorporation mechanisms. Detailed analysis of anion incorporation along different configurations is presented, as well as important effects arising from anion to cation flux ratio.
Sharp profiles and low-temperature diffusion of Ga and Sb in silicon modulation-doped superlattices
Authors: Streit D. C. , Ahlers E. D. , Allen F. G.
Published: July 2002

We demonstrate the growth of nipi-doped superlattices in silicon using in situ solid phase epitaxial (SPE) regrowth of molecular-beam deposited films. For 1000-Å layer widths both Ga and Sb exhibit sharp profiles. With 100 Å layers Sb profiles are well-defined but Ga layers are somewhat smeared. Maximum dopant concentrations of 1×1020 cm−3 for Ga and 3×1020 cm−3 for Sb were obtained. Secondary ion mass spectrometry profiling and Hall measurements are used in conjunction with furnace annealing to set an upper limit on the diffusion constants for Ga and Sb in SPE regrown silicon at 690 °C at 1.2×10−18 and 3×10−19 cm2/s, respectively. Diffusion of Ga in evaporated amorphous silicon is considerably enhanced over that in single crystal silicon, and was determined to fit the expression D=9.1×10−5 exp(−1.92±0.15 eV/kT) cm2/s.
Very high voltage (500 kV) electron beam lithography for thick resists and high resolution
Authors: Jones G. A. C. , Blythe S. , Ahmed H.
Published: July 2002

Electron beams at very high voltages, up to 500 kV, have been used to expose PMMA electron resist. It has been shown that near vertical line shapes can be formed in resist layers which are several microns thick. Monte Carlo simulations have been performed for electron scattering, energy distribution, and line profiles for beam voltages from 50 to 500 kV and beam sizes from 0.01 to 1 μm. These indicate that beam voltages up to 250 kV are necessary to fully expose a nanometer scale pattern with an aspect ratio of line height to width exceeding ten times. The dose required to expose a complete line has been found to increase almost linearly with increasing voltage. A novel direct fabrication technique which does not require resist has been demonstrated using high voltage beams. The silicon substrate is damaged in localized regions by using electron beams at energies greater than 250 kV. These parts are etched away using a selective silicon etch and patterns are formed in the substrate. This fabrication method is believed to be potentially capable of allowing sub-100 Å structures to be formed by electron lithography in silicon.
Nucleation effects in visible-laser chemical vapor deposition
Authors: Oprysko Modest M. , Beranek Mark W.
Published: July 2002

A low power, focused, argon ion laser beam ∼514.5 nm has been used to controllably and reproducibly deposit micron-size metallic films on transparent glass and quartz substrates. Film growth proceeds via the pyrolytic decomposition of organometallic molecules on nucleation sites. The nucleation sites can be created over the entire substrate by flood exposure with deep ultraviolet light in the presence of organometallic vapor or in micron size areas by forming an initial deposit and then scanning the substrate across the focused laser beam. The latter nucleation technique has been extended to the deposition of metal on chrome-on-glass photomasks. Here metal deposition proceeds in three distinct time periods: surface modification (fast), nucleation (slow), and film growth (fast). The visible-laser chemical vapor deposition technique has been used to demonstrate the repair of defects in photomasks with a resolution approaching 1 μm.
Effects of dry etching on the electrical properties of silicon
Authors: Heddleson J. M. , Horn M. W. , Fonash S. J. , Nguyen D. C.
Published: July 2002

Dry etching results in the permeation of silicon by etching species; it also results in the better understood residue layer formation and near-surface lattice damage layer formation. The principal species permeating silicon during dry etching exposures is found to be hydrogen. Using doping deactivation as a marker, we study this permeation and show that hydrogen can permeate as much as 10 μ during etching, thereby modifying the electrical properties of Si to that depth. We further demonstrate that this hydrogen permeation, at least in the case of p material, exhibits two distinct regions of behavior and two apparent diffusion coefficients. It is also shown that the doping deactivation anneals out differently in these two permeation regions.
Fabrication of quantum devices in metals and semiconductors
Authors: Schmid H. , Rishton S. A. , Kern D. P. , Washburn S. , Webb R. A. , Kleinsasser A. , Chang T. H. P. , Fowler A.
Published: July 2002

Advances in nanolithography using electron-beam techniques have allowed a great variety of quantum devices to be fabricated and tested. The critical dimensions governing the design of these devices will be discussed. Fabrication and experimental results of several such devices for studies will be reported. These include structures aiming at the observation of the electrostatic Aharonov–Bohm effect and nonlocal oscillations, superconducting weak links, and devices for the investigation of quantum scattering effects.
Preoxidation treatments for very thin oxides grown after silicon exposure to reactive ion etching plasma
Authors: Bellezza O. , Ghezzi P. , Gualandris F. , Riva C.
Published: July 2002

Very thin silicon dioxide (<100 Å) has been widely used as a tunnel barrier for floating gate electrically erasable read only memory (EEPROM) devices. Small tunneling areas are required in the new EEPROM cell generations and the use of reactive ion etching (RIE) plasma is mandatory in order to define windows with a diameter <1.2 μm. The tunnel oxide has to be grown in these windows opened in the thicker (150–300 Å) gate oxide. The surface damage induced by plasma RIE requires postetch treatments. In this paper, we deal with the effects induced on the oxide characteristics by different postetch treatments. The analysis has been focused on both the recovery of the surface damage and the electrical characteristics of a 95-Å-thick tunnel oxide grown after different postetch processes. The oxide degradation under current stress has been evaluated using metal–oxide–semiconductor capacitors. The best preoxidation treatment that we found among our experiments has also been tested on an EEPROM cell. The tunnel oxide degradation, i.e., the cell threshold voltage shift, was found to be very negligible after 105 write–erase cycles.
Selective reactive ion etching of GaAs on AlGaAs using CCl2F2 and He
Authors: Seabaugh Alan
Published: July 2002

The characteristics of a CCl2F2:He reactive ion etch are reported for use in selectively etching GaAs/AlGaAs heterostructures. The etch is performed at a pressure of 150 mTorr, with rf power of 0.5 W/cm2. Both He and CCl2F2 flow rates are controlled to 10 sccm, with measured dc self-bias of typically 125 V. The etch rate for GaAs is 1.8 μm/min, while the AlGaAs etch rate depends on the Al mole fraction x with measured values of 150 Å/min at x=0.28 and 45 Å/min at x=0.5. The selectivity is 120 at x=0.28 and 420 at x=0.5. The etch shows an anisotropy between the 〈011〉 and the 〈011̄〉 directions. Measurements of the plasma impedance are reported as a function of pressure, power, and gas flow rate. From these measurements, the dc bias can be computed and is shown to give good agreement with the measured values. The plasma conditions are sensitive to the previous history of the chamber, but by preconditioning the chamber, the etch is readily reproduced.
A new ultrafine groove fabrication method utilizing electron cyclotron resonance plasma deposition and reactive ion etching
Authors: Ohki Shigehisa , Oda Masatoshi , Shibata Toshitaka
Published: July 2002

A new method for fabricating ultrafine grooves with a high depth to width ratio is proposed. The main feature of this method is to use V-shaped SiO2 grooves as etching masks. These grooves are prepared by depositing a SiO2 film onto the patterned substrate employing electron cyclotron resonance (ECR) plasma deposition, followed by removing the sidewall deposited ECR-SiO2 films with buffered HF solution. The gap width formed at the bottom of the V grooves were controlled by varying the HF etching time. Fine grooves having 0.2 μm or narrower widths were successfully fabricated into Si substrates and Ta films. Suppressing the localized undercutting is vital for fabrication of nanometer scale structures.
The impact of high-sensitivity resist materials on x-ray lithography
Authors: Seligson Daniel , Ito Hiroshi , Willson C. Grant
Published: July 2002

Major research and development efforts are underway throughout the world that are directed toward establishment of very large scale integrated manufacturing with x-ray lithography. Point-source x-ray lithography was once the favored approach to this technology but point sources have been all but abandoned in favor of synchrotron sources. This paper reviews the reasons for the emphasis on synchrotron sources and reexamines the reasons for this emphasis. Recent developments in point-source technology and in resist chemistry warrant this reexamination. We conclude that point-source x-ray lithography is feasible and renewed effort is warranted in point-source and high-resistivity resist research and development.
Nanowriter: A new high-voltage electron beam lithography system for nanometer-scale fabrication
Authors: Chen Z. W. , Jones G. A. C. , Ahmed H.
Published: July 2002

A new high-voltage electron beam lithography system, Nanowriter, has been designed and constructed to give a large scan field size without compromising the ability to write nanometer-scale structures. Nanowriter comprises a 100-kV LaB6 electron gun with a zoom condenser arrangement consisting of two condenser lenses which are used to provide a system demagnification of up to 10 000 times. To combine a very small on-axis spot diameter of 4 nm and a large scanned field of 250×250 μm without dynamic correction, a newly developed swinging objective immersion lens (SOIL) concept based on variable axis immersion lens (VAIL) and swinging objective lens (SOL) has been utilized. The SOIL used here has four advantages: first, it is possible to reduce the working distance, thereby decreasing spherical aberration; second, the scanned field is increased without significantly increasing deflection aberrations; third, it permits easy alignment of the column, and fourth, an inherent attribute of the SOIL is the shielding from extraneous magnetic fields given to the target. The substrate resides on an in-lens stage which is supported on the boreless lower pole piece of the SOIL. The system has been used to delineate nanometer-scale patterns in poly(methylmethacrylate) (PMMA) resist. Lines of 15-nm width have been written into 50-nm-thick PMMA on thick Si substrates. These linewidths were almost unchanged over the whole scanned area of 250×250 μm.
Nanostructure fabrication of zero-dimensional quantum dot diodes
Authors: Randall J. N. , Reed M. A. , Matyi R. J. , Moore T. M.
Published: July 2002

The nanofabrication techniques which are used to create quantum dot diodes will be discussed. The device is a vertical resonant tunneling diode where the lateral dimensions are reduced to ∼1000 Å. Electron beam lithography is used to pattern a small self-aligned metal dot top contact and etch mask. The semiconductor dot is a cylinder ∼1000 Å in diameter and on the order of 100 Å thick, with the vertical potential defined by the double-barrier heterostructure and the lateral defined by the Fermi-level pinning of the free surfaces. Discrete energy states due to the three-dimensional confinement are observed and are spin degenerate only. Transport measurements through such a device will be presented.
Miniature Hall sensor fabricated with maskless ion implantation
Authors: Kanayama Toshihiko , Hiroshima Hiroshi , Komuro Masanori
Published: July 2002

Miniature Hall sensors with half-micron sensing areas have been fabricated with maskless Si ion implantation into semi-insulating GaAs. It is shown that maskless ion implantation is a very efficient and productive technique for fabrication of small Hall sensors with practical performance, in that it achieves, with minimum process steps, accurate pattern definition and variation in the in-plane doping profile. The former is required to minimize the misalignment voltage and the latter is to realize high sensitivity and low input resistance. The maximum sensitivity obtained is 48 mV/T and is independent of the carrier concentration if the device structure is properly designed and fabricated. This agrees with the theoretical consideration that the high field effect determines the performance.
GaAs/AlGaAs material modifications induced by focused Ga ion beam implantation
Authors: Hirayama Y. , Okamoto H.
Published: July 2002

Two aspects of the material property modifications of the GaAs/AlGaAs system induced by Ga focused ion beam implantation have been studied. One is the formation of a highly resistive region in an n-type GaAs layer, and the other is the enhanced interdiffusion of GaAs/AlGaAs heterointerfaces. Both modifications enable us to change material properties with a minimum dimension of <100 nm. Quantum-well-wire structures were successfully fabricated by using the latter technique.
Reproducible growth conditions by group III and group V controlled incorporation rate measurements
Authors: Fernandez Rouel
Published: July 2002

Reflection high-energy electron diffraction intensity oscillations have been used to measure group III and group V controlled incorporation rates. The growth condition for measuring the incorporation rates under control of the group III flux is to have an excess of the group V flux. Conversely, the condition for measuring the incorporation rates under control of the group V arrival rate is to have an excess of the group III flux. At normal growth temperatures the group III controlled incorporation rates are not substrate temperature dependent, while the group V controlled incorporation rates exhibit a growth temperature dependence. The use of incorporation rate ratios is of greater value for growth characterization than the traditional beam equivalent flux ratios, which does not reflect the substrate temperature dependence. Furthermore, group V controlled incorporation rates can be used to set accurate reproducible growth conditions.
Photoemission investigation of Ge and SiGe alloy surfaces after reactive ion etching
Authors: Robey S. W. , Bright A. A. , Oehrlein G. S. , Iyer S. S. , Delage S. L.
Published: July 2002

Photoemission spectra were obtained from Ge surfaces after reactive ion etching with CF4 and CF4/H2 mixtures. These measurements indicate a surface layer of fluorinated Ge species as well as adsorbed carbon and CFx species. The shifted intensity in the Ge(2p3/2) core level suggests a layer of about 1 to 2 layers of GeFx, with x∼2–3. The accumulation of CFx overlayer increases with increasing H2 to CF4, but comparisons with Si etched under identical conditions indicate that there is less steady-state film deposition of Ge during reactive ion etching than on Si. Thus, an increased thickness of carbonaceous overlayer on Ge compared to Si is unlikely to be the explanation for the observed drop in the selectivity toward etching Ge over Si with increasing hydrogen addition. Reactive ion etching of a Si35Ge65 alloy was also investigated. Here, photoemission indicated a surface layer of GeFx similar to that found on pure Ge, but little evidence of SiFx species. The composition of the surface is enriched in Ge for about 3–5 layers.
Baffle-free refractory dimer arsenic source for molecular-beam epitaxy
Authors: Mattord T. J. , Kesan V. P. , Crook G. E. , Block T. R. , Campbell A. C. , Neikirk D. P. , Streetman B. G.
Published: July 2002

A refractory, two-zone, large-capacity, baffle-free arsenic cracking source for molecular-beam epitaxy is presented. The new features of this design include the use of a molybdenum tube to provide efficient cracking, a horizontal sublimator at a right-angle geometry to the cracking section, a baffle-free design, and the use of expanded tantalum heating filaments. High-efficiency cracking is obtained at cracking tube temperatures between 750 and 1050 °C. Bulk GaAs and GaAs/AlGaAs heterostructures grown using this source exhibit good electrical and optical properties, with clear improvements in electrical behavior when compared to an As4 source. We believe this source design can be easily applied to other column V materials such as phosphorus and antimony.
Comparison of damage in the dry etching of GaAs by conventional reactive ion etching and by reactive ion etching with an electron cyclotron resonance generated plasma
Authors: Cheung R. , Lee Y. H. , Lee K. Y. , Smith T. P. , Kern D. P. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

We have developed a high-resolution etch for GaAs in an electron cyclotron resonance-radio frequency (ECR-rf) hybrid reactor using CCl2F2/He as the etch gas. Surface contamination from the gas and from the electrodes was found to affect the etching process as well as etched substrate. Surface damage studies using Schottky diode and x-ray photoelectron spectroscopy analysis and sidewall damage characterization using room-temperature conductance measurements of n+-GaAs quantum wires indicate that very little damage is caused by ECR-rf reactive ion etching compared with conventional rf reactive ion etching (RIE). In addition, the small residual damage after ECR-rf RIE is measured to increase with etching time.
Thermal effects in electron beam lithography
Authors: Mulder E. H. , van der Mast K. D. , Enters A. C.
Published: July 2002

At the Delft University of Technology, an electron beam (e-beam) writer is being designed, which uses a constant 10 μA beam current at 100 kV and shape sizes of 0.1×0.3 to 1.0×1.0 μm. The brightness of the source is modulated to keep the probe current constant. The maximum current density will be 3.3 104 A/cm2. Therefore, thermal effects are a primary concern. High-energy electrons lose most of their energy at depth in the substrate. The exposure times are, due to the high current density, too short to make thermal diffusion from the bulk significant. Therefore, only the local energy deposition in the resist and the contributions from previously exposed points influence the temperature rise. Presently, the writing speed of lithography systems is restricted by the resist sensitivity. The lower limit to the dose for writing is determined by the statistical noise in the number of electrons, to define the smallest detail. For 0.1 μm lines, the ideal sensitivity of the resist is 0.1 C/m2, thus allowing a writing speed of 1 cm2 /s. Using the ideal resist on silicon, the temperature rise caused by one exposure was calculated to be less than 17 K, at the edge of the exposed point. The heating is higher for low accelerating voltages, since the penetration depth is smaller and the direct energy loss is higher.
Strain effects and optical properties of Si1−xGex/Si superlattices
Authors: Rajakarunanayake Y. , McGill T. C.
Published: July 2002

We demonstrate that quasi direct band gap Si1−xGex/Si superlattices can be obtained by suitable choices of layer thicknesses. We calculate strain dependent conduction-band offsets as functions of the substrate alloy concentration, and of the epilayer alloy concentration. Optical matrix elements are computed for Si0.5Ge0.5/Si superlattices grown on Si0.75Ge0.25 buffer layers with superlattice layer thicknesses of 4 to 24 monolayers. We find that optical absorption and emission strengths can vary by three to four orders of magnitude for layer thickness variations as small as 1–2 monolayers, suggesting that layer thicknesses must be controlled to within one monolayer to obtain enhanced optical properties. Typical optical matrix elements calculated for these Si1−xGex/Si superlattices are three to four orders of magnitude larger than for bulk Si or Ge, but, are still three orders of magnitude smaller than for direct band gap materials such as GaAs.