Showing papers in "Journal of Vacuum Science & Technology B in 1985"
193 citations
TL;DR: In this article, anisotropic surface films, physisorbed molecules, and chemisorption induced changes in the electronic polarizability of the outermost plane of substrate atoms are identified.
Abstract: I describe some results of the first systematic study of above‐bandgap optical anisotropies in cubic semiconductors The anisotropies are large, of the order of 1% of the relative reflectance differences for light polarized along orthogonal principal axes of the dielectric tensor of the anisotropic phase Extrinsic contributions arising from anisotropic surface films, physisorbed molecules, and chemisorption‐induced changes in the electronic polarizability of the outermost plane of substrate atoms are identified The line shapes of these reflectance‐difference (RD) spectra provide the first critical test of models proposed to describe intrinsic contributions to the optical anisotropies of these materials The dominant intrinsic contribution is shown to be a surface (interface) many‐body effect due to the reduced screening of the surface atoms as a result of the termination of the bulk lattice A secondary intrinsic contribution from the influence of spatial dispersion on interband energy gaps in the one‐e
180 citations
TL;DR: In this article, a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces is presented, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides.
Abstract: We present a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides. The self‐consistent calculations, based on the local density functional and ab initio pseudopotentials, determine the minimum energy configurations, and the relative position of the Si and Ge bands. The presence of the strains influences the interface dipole, and also causes significant shifts and splittings of the bulk bands. For (001) interfaces we find for the top of the valence bands: Ev, Ge−Ev, Si=0.74 and 0.21 eV, respectively, for the cases corresponding to Ge strained to match a Si substrate and vice versa. A discussion of these results and comparison with experiment is presented.
144 citations
TL;DR: In this article, an epitaxial Ge and Si films have been grown by primary ion deposition from laser-induced plasmas, where neutral atoms and ions were emitted from Ge targets with mean velocities of 1.0-1.6×106 cm−1 (corresponding to average kinetic energies of 40 to 100 eV).
Abstract: Epitaxial Ge and Si films have been grown by primary ion deposition from laser‐induced plasmas. The plasmas were formed by focusing 15 ns, 107–108 W cm−2, pulses of 5 eV photons from a KrF excimer laser onto Ge or Si single crystal wafer targets. Time‐of‐flight, current‐voltage, and film‐thickness distribution measurements established that neutral atoms and ions were emitted from Ge targets with mean velocities of 1.0–1.6×106 cm s−1 (corresponding to average kinetic energies of 40 to 100 eV) in a distribution that was strongly peaked in the direction normal to the target surface. Macroscopic (∼1 μm diam) particles were also emitted. A shutter, synchronously triggered with the laser pulses through a delay circuit, was used as a velocity filter for removing from the beam particles with velocities up to 1.2×104 cm s−1. Epitaxial Ge films were grown on semi‐insulating (100) GaAs substrates at temperatures between 300 and 450 °C and epitaxial Si was grown on (100) Si at 700 °C. Deposition rates were typically ...
128 citations
TL;DR: In this paper, the dependence of the etch rate of polyimide on the relative concentrations of these two gases was compared with data from optical emission spectra,mass spectra and x-ray photoelectron spectroscopy(XPS).
Abstract: Gas phase and surface phenomena responsible for etching polyimide in O2–CF4 rf plasmas have been investigated. The dependence of the etch rate of polyimide on the relative concentrations of these two gases was compared with data from optical emission spectra,mass spectra, and x‐ray photoelectron spectroscopy(XPS). The increase in O atom number density in the plasma with addition of CF4 to O2 certainly increases etch rates over those achieved in pure oxygen plasmas. However, etch rates do not track identically with atomic oxygen emission intensities. Etch rates are enhanced through the reaction of fluorine in the polyimide surface layer while fluorine present in excess inhibits etching through competition with oxygen atoms, resulting in the formation of CF2 type bonding at the surface. Removal of the resulting passivation is most efficiently accomplished by exposure of the polyimide to a plasma with higher oxygen concentration, probably due to the presence of ions. The position of the maximum in etch rate distribution with respect to CF4 concentration depends on an optimum ratio of O to F atoms in the plasma.
125 citations
TL;DR: In this paper, a 0.12 μm aperture in a metal film supported by a glass slide is used to define a submicroscopic source of light for a demonstration of scanning ultramicroscopy in the reflection mode.
Abstract: A 0.12 μm aperture in a metal film supported by a glass slide is used to define a submicroscopic source of light for a demonstration of scanning ultramicroscopy in the reflection mode. The aperture is viewed through a microscope in dark field illumination by a totally reflected beam (λ=633 nm). When an interface is brought in proximity to the aperture, the light emission from the aperture is quenched to an extent which depends on the nature of the interface and the polarization of the incident beam. With a 1 μm wide hole in a thin dielectric or metal film as test object, an edge resolution of 0.1 μm is obtained only with scans perpendicular to the direction of the irradiating beam.
121 citations
TL;DR: Optical second harmonic generation for surface and interface studies is briefly reviewed in this article, with numerous examples illustrating how powerful and versatile this new surface analytical technique can be for surface analysis.
Abstract: Optical second harmonic generation for surface and interface studies is briefly reviewed, with numerous examples illustrating how powerful and versatile this new surface analytical technique can be.
103 citations
TL;DR: The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented in this article, where the flux composition as a function of epitaxial layer composition was determined for the lattice matching quaternary.
Abstract: The growth of useful GaxIn1−xPyAs1−y by MBE is inhibited by the difficulty in maintaining precise control over the flux from condensed source As and P effusion ovens. The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented. Accommodation coefficients were determined for P2 and As2 on heated InP and GaAs surfaces. The flux composition as a function of epitaxial layer composition was determined for the lattice‐matching quaternary. Studies of doping were done and injection laser structures were grown. Although detailed studies of layer composition control were not done, the achievable control seems quite adequate for injection lasers. A variety of heterostructure lasers emitting at nominally 1.5 μm with broad area 300‐K threshold‐current densities from 1300 to 2400 A/cm2 were demonstrated. Ridge waveguide lasers fabricated from the same wafers had Ith of about 40 mA and differential efficiencies of 36%–45%. They lased cw to 50 °C.
103 citations
TL;DR: In this article, an ion-beam-assisted diamond etching system was proposed to achieve an etching rate of 200 nm/min with a ratio of 20 between the diamond and an aluminum mask.
Abstract: 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.
100 citations
TL;DR: In this article, a modulated-beam, mass spectrometer system was used to obtain information about etch products, reaction probabilities, and etching mechanisms for the reactions of Cl2 with Al(100) and Cu(100), and for the reaction of XeF2 with W(111) and Nb.
Abstract: A modulated‐beam, mass spectrometer system has been used to obtain information about etch products, reaction probabilities, and etching mechanisms for the reactions of Cl2 with Al(100) and Cu(100) and for the reaction of XeF2 with W(111) and Nb. The influence of ion bombardment on the etching reaction has also been investigated.
99 citations
TL;DR: In this article, the experimental evidence and techniques which established this fraction and the subsequent evidence that has led to questioning of its previous, almost universal, acceptance are reviewed and the experimental evidences for the offset ratio in this system being dependent upon growth sequence are discussed.
Abstract: Early work by Dingle and co‐workers on the GaAs‐(AlGa)As heterojunction established the fraction of the energy gap difference appearing in the conduction band to be 0.85. The experimental evidence and techniques which established this fraction and the subsequent evidence that has led to the questioning of its previous, almost universal, acceptance will be critically reviewed. Experimental evidence for the offset ratio in this system being dependent upon growth sequence will be discussed. Existing theoretical models will be discussed in the context of the above experimental work.
TL;DR: In this article, the growth rate of GaAs in a UHV system from molecular beams of trimethyl gallium (TMG) and arsine (AsH3) was investigated.
Abstract: In this paper we report on the growth of GaAs in a UHV system from molecular beams of trimethyl gallium (TMG) and arsine (AsH3). Deposition could only be achieved if the AsH3 was partially decomposed before injecting it into the system. If arsenic is provided in excess, the growth rate depends linearly on the TMG beam pressure. The growth rate saturates the system if the arsenic pressure in the beam is reduced; the saturation value being proportional to the arsenic flux. The results can be explained by a model assuming that sticking of TMG at the growing surface is allowed only if As simultaneously is supplied in excess. The layers are heavily doped with carbon ( p≊1019–1020 cm−3). The carbon uptake is reduced by several orders of magnitude if TEG is used rather than TMG.
TL;DR: In this article, a self-developing metal halide resists using a sub-nanometer diameter 100 keV electron beam was demonstrated at the 1-2 nm size scale.
Abstract: Patterning at the 1–2 nm size scale has been demonstrated with self‐developing metal halide resists using a subnanometer diameter 100 keV electron beam. Electron energy loss spectroscopy during lithographic exposure indicates removal of the halide ion first, followed by displacement of the metal ions. Under appropriate exposure of AlF3, we have demonstrated that aluminum metal structures can be fabricated in situ. Nanometer scale patterns have been replicated into Si3N4 via reactive ion etching using AlF3 as the resist mask.
TL;DR: In this paper, the specular beam intensity of GaAs surfaces during and after growth by MBE has been probed by detailed measurements of specularbeam intensity in RHEED patterns from the surfaces.
Abstract: The dynamic behavior of GaAs surfaces during and after growth by MBE has been probed by detailed measurements of the specular beam intensity in RHEED patterns from the surfaces. The damping of the intensity oscillations observed after growth has commenced is shown to be a strong function of arsenic pressure with high pressure causing strong damping and rough growth fronts. The specular beam intensity after steady‐state growth has been interrupted shows first an initial fast increase with the largest increase occurring at low arsenic pressure, and then a slow recovery to its equilibrium no‐growth intensity at a rate that increases with arsenic pressure. Measurements of the intensity recovery after short growths on an equilibrated no‐growth surface provide new information about the growth front behavior during the first few monolayers of growth. The surface recovers in the shortest time after deposition of either a small fraction of a monolayer or slightly more than an integer number of monolayers. Recovery...
TL;DR: In this article, it was shown that the way in which energetic ion bombardment accelerates the etching of Si in a fluorine environment is by a direct acceleration of the product formation step and not by damage-enhanced chemistry.
Abstract: Evidence is presented which indicates that the way in which energetic ion bombardment accelerates the etching of Si in a fluorine environment is by a direct acceleration of the product formation step and not by damage‐enhanced chemistry. The use of fluorine coverage to characterize the etching process is discussed in detail and the assumption that the etch rate of Si can be decoupled into a spontaneous and an ion‐assisted contribution is questioned. Finally, examples of the influence of ion bombardment on Al(100)–Cl2, Cu(100)–Cl2 at 310 °C, and Nb–XeF2 are used to emphasize that some of the conclusions reached for the Si–XeF2 system are not generally applicable to all gas–solid combinations.
TL;DR: Refined and very exact processing procedures for producing geometrically highly precise silicon structures are described in this article, where the structures are micromachined utilizing wet chemical orientation and/or concentration etching techniques.
Abstract: Refined and very exact processing procedures for producing geometrically highly precise silicon structures are described. The structures are micromachined utilizing wet chemical orientation and/or concentration etching techniques. The use of a specially designed and highly effective etching system is a significant refinement in the processing procedure. The structures have excellent large and small scale uniformity. Relief structures having features as small as 0.2 μm have been produced. We report on devices for three specific research applications: (1) Very high Q torsional oscillators useful for high sensitivity measurements in the study of the mechanical properties of single crystal silicon and also in the study of thin freely suspended liquid crystal films, (2) unstrained focusing x‐ray mirrors, and (3) μm level mechanical ‘‘shadow masks’’ useful for noncontaminative, in situ patterning of thin films deposited in MBE and/or other deposition systems.
TL;DR: In this paper, the role of surface molecular reaction kinetics associated with the dissociative chemisorption of the group V molecular specie is explicitly investigated for the first time and shown to lead to a new configurationdependent reactive incorporation (CDRI) growth process, quite distinct from the conventional notions of nucleation and continuous growth.
Abstract: Results of Monte Carlo simulations carried out to examine the nature of the growth mechanism in MBE of lattice matched III–V compounds are presented. The role of surface molecular reaction kinetics associated with the dissociative chemisorption of the group V molecular specie is explicitly investigated for the first time and shown to lead to a new configuration‐dependent‐reactive‐incorporation (CDRI) growth process, quite distinct from the conventional notions of nucleation and continuous growth. For very slow dissociative reaction kinetics the CDRI growth process is shown to lead to a reaction‐limited‐incorporation (RLI) growth mechanism and the accompanying growth rate exhibits oscillatory behavior. For fast dissociative reaction kinetics, accompanied with a sufficiently fast surface interlayer migration kinetics of the group III atoms, the CDRI growth process gives rise to a configuration‐limited‐reactive‐incorporation (CLRI) growth mechanism. The crystal growth rate once again exhibits oscillations. It is also shown that under conditions involving specially delicate balance between the various kinetic rates, growth can proceed without oscillations in the growth rate. An essentially layer‐by‐layer mode of material addition is realized in all the aforementioned cases. Consequences of the resulting growth front morphology for the time dependence of the RHEED specular beam intensity are investigated and shown to give rise to a damped oscillatory behavior, including in the absence of oscillations in the crystal growth rate.
TL;DR: In this article, the decomposition of trimethylaluminum (TMA) on copper, aluminum, quartz, and gallium arsenide substrates has been studied as a function of substrate temperature from 550-900 K under low pressure conditions.
Abstract: The decomposition of trimethylaluminum (TMA) on copper, aluminum, quartz, and gallium arsenide substrates has been studied as a function of substrate temperature from 550–900 K under low pressure conditions. Detection of gaseous products was carried out by laser multiphoton ionization mass spectrometry (MPI/MS) for methyl radical and aluminum species and electron impact mass spectrometry (EI/MS) for stable species. The methyl radical was the sole gaseous reaction product observed above these substrates, with an apparent activation energy for production of 13±2 kcal/mol. Neither ethane nor methane was observed at the low pressures employed in these experiments, with either helium or hydrogen as carrier gases. A mechanism is proposed to explain these results.
TL;DR: In this article, a connection between Schottky barriers and semiconductor heterojunction band lineups is proposed as a possible test of theory, without postulating a defect pinning mechanism.
Abstract: Two recent models of Schottky barrier formation are discussed. These invoke ‘‘metal‐induced gap states’’ or native defects to explain Fermi‐level pinning. Available experimental data can be satisfactorily explained by states intrinsic to the surface and interface, without postulating a defect pinning mechanism. In contrast, recent theoretical and experimental work appears to contradict the proposed defect mechanism. The connection between Schottky barriers and semiconductor heterojunction band lineups is proposed as a possible test of theory.
TL;DR: In this article, the authors established a thermodynamic framework for growth of GaAs and Ga1−xAlxAs by molecular beam epitaxy MBE, for the region where loss of gallium is significant.
Abstract: The thermodynamic framework is established for growth of GaAs and Ga1−xAlxAs by molecular beam epitaxy MBE, for the region where loss of gallium is significant. It is shown that the temperature dependence of gallium loss from GaAs is a function of the experimental beam pressures and not a basic property of the system. At a given temperature, gallium loss (and hence the growth rate for GaAs) is a function of arsenic pressure and in the alloys it is also a linear function of Al content. As2 is the equilibrium species used in the calculations. Comparison with experimental data is therefore limited, but it is clear that As4 dissociation is kinetically hindered when used in practice. Use of a closely controlled pressure of As2 is indicated to achieve good control of both layer thickness and alloy composition. The approach is likely to be more important in other alloy systems where lattice matching to the substrate is more critical.
TL;DR: In this article, the valence band offset in AlAs/GaAs heterojunctions was found to be 0.45±0.05 eV from analysis of charge transfer versus undoped spacer layer thickness.
Abstract: The valence band offset in AlAs/GaAs heterojunctions is found to be 0.45±0.05 eV from analysis of charge transfer versus undoped spacer layer thickness. This result and several recent experiments on AlxGa1−xAs/GaAs heterojunctions indicate that the valence band offset is approximately linear in AlAs fraction x over the entire alloy composition range and more than twice the previously accepted value. The relation between heterojunction band offsets and Fermi level pinning for metals on semiconductors is discussed.
TL;DR: In this paper, a 30 kV fine focused ion beammachining system was constructed in which a Ga ion beam extracted from a needle-type liquid metalsource is focused into a submicron spot by a three-electrode electrostatic lens and deflected by an octapole deflector.
Abstract: A 30 kV fine focused ion beammachining system was constructed in which a Ga ion beam extracted from a needle‐type liquid metalsource is focused into a submicron spot by a three‐electrode electrostatic lens and deflected by an octapole deflector. Vacuum rate at the work stage is 10− 7–10− 8 Torr. With blanking electrodes, the machined area can be confined to any rectangular area determined by the cursol lines on the scanning ion microscopic display. Probe current is higher than 0.3 nA for a 0.3 μm diam spot and current density is over 0.71 A/cm2. At a scanning speed of 100 μm/s, grooves 0.2 μm wide are made in a gold film 0.1 μm thick. By scanning repeatedly, a groove is produced in a (100)Si wafer yielding a cross section having a very sharp V shape with an aspect ratio of 8:1. Two‐dimensional scanning removal is performed under various conditions at the same dose of 1.9×101 8 ion/cm2, resulting in very different hole shapes. Removal at a scanning speed of 1 mm/s with 200 repetitions produces a uniform shallow hole shape, while removal at 5 μm/s with one repetition results in an inclined deep hole shape. Observation of the cross section shows that this inclined area protrudes from the side wall of the hole, formed through the redeposition of sputtered silicon. These results show the importance of the redeposition process in removal utilizing fine focused ion beams. Also, the differing results of two scanning methods appear to demonstrate the nonlinear sputter effect in fine focused ion beammachining.
TL;DR: In this paper, the angular profiles of the specular beam were measured during the first two periods of oscillations and analyzed in terms of the two-level diffraction calculation of Lent and Cohen.
Abstract: Oscillations in both the intensity and width of reflection high‐energy electron diffraction beams that are measured during the MBE growth of GaAs are observed to depend upon most growth parameters. The envelope of the intensity oscillations, for example, depends upon the flux ratios, the substrate temperature, the sample misorientation, the scattering geometry, the sample flatness, and the flux uniformity. To separate these dependencies we have made RHEED measurements on small, exceedingly flat, near singular samples. The angular profiles of the specular beam were measured during the first two periods of oscillations. These data were analyzed in terms of the two‐level diffraction calculation of Lent and Cohen. The measured profiles are in excellent agreement with that calculation. For oscillations with a 26‐s period, moderate changes in the substrate temperature and As flux can cause significant changes in the pair correlation length on the surface.
TL;DR: In this article, high aspect-ratio anisotropic etching for GaAs has been obtained with Cl2 plasma in a new reactive ion beam etching (RIBE) system equipped with an ultrahigh vacuum chamber.
Abstract: High aspect‐ratio anisotropic etching for GaAs has been obtained with Cl2 plasma in a new reactive ion beam etching (RIBE) system equipped with an ultrahigh vacuum chamber. A vertical wall with 0.5 μm thickness and 7 μm height was obtained at a 500 V ion extraction voltage and etching gas pressure of 8×10−4 Torr. A normalized etching rate was 2 ( μm/min)/(mA/cm2) which corresponds to a sputtering yield of 23 atoms/ion. Such a high aspect‐ratio etching was mainly owing to use of a high‐temperature (250 °C) baked photoresist mask with a sharp cut profile. GaAs and AlGaAs equirate etching, which is often difficult in the conventional reactive ion etching (RIE), has also been obtained using this system. It was found that decrease of the AlGaAs etching rate in the RIE is attributed to Al2O3 formation due to residual H2O during etching.
TL;DR: In this article, a detailed study of the polarization dependences of the second harmonic generation process from clean Si(111)•7×7 surfaces is presented and analyzed in terms of the symmetry properties of the surface.
Abstract: A detailed study of the polarization dependences of the second‐harmonic generation process from clean Si(111)‐7×7 surfaces is presented and analyzed in terms of the symmetry properties of the surface. Results from real‐time, in situ measurements on disordering of the Si(111)‐7×7 surface by oxidation and Ar+ ion bombardment are also reported.
TL;DR: In this article, the effect of the faceted shape of the ZrO/W TFE on the angular distribution of the emission and virtual source size was examined, and the computer derived results agree qualitatively with experimental angular emission distributions measured for various emitter radii.
Abstract: The ZrO/W thermal field emitter (TFE) has proven to be a useful high brightness electron source for a variety of microprobe applications. Desirable source characteristics are: 1 to 2 mA/sr angular intensity, 1 to 1.5 eV energy spread for an emitter radius of 0.6 to 1 μm, and <0.5% noise level between 1 Hz and 25 kHz. In this study we examine the effect of the faceted shape1 of the ZrO/W TFE on the angular distribution of the emission and virtual source size. In particular the scwim computer program1 is employed to compare the emission characteristics of faceted and spherical shaped emitters. The computer derived results agree qualitatively with experimental angular emission distributions measured for various emitter radii. It is shown that the high angular intensity obtained from the ZrO/W TFE is due in part to a large angular demagnification caused by the faceted emitter region. Nevertheless, a comparison of the virtual source size of the faceted and the spherical shapes shows only a small source image i...
TL;DR: In this article, a local density model of the charge density, electron potential, and energy of metal-semiconductor contacts is constructed, which makes the height of the rectifying Schottky barrier directly proportional to the observed vacuum work function of the metal.
Abstract: A one‐dimensional local‐density model of the charge density,electrostatic potential, and energetics of metal–semiconductor contacts is constructed. This model is an extension of analogous models of bimetallic junctions to include the gap in the semiconductor excitation spectrum, space charge effects in the semiconductor, and fabrication‐induced charges near the interface. Self‐consistent analysis of the valence‐electron charge redistribution at the model metal–semiconductor interface relative to the corresponding vacuum surfaces reveals a cancellation which makes the height of the rectifying Schottky barrier directly proportional to the observed vacuum work function of the metal in the absence of additional charges induced by atomic relaxations or chemical reactions which occur during the fabrication of the interface. The experimentally observed stability of the Schottky barrier heights against changes is applied bias and semiconductor doping are predicted correctly. The occurrence of interfacial atomic rearrangements and/or chemical reactions is incorporated into the model via the inclusion of charge centers near the interface. Four types of centers are considered: donors, acceptors, and three‐state centers with both positive (U>0) and negative (U<0) effective electron–electron interactions. Applications of the model to describe measured barrier heights on GaSe(0001) and GaAs(110) require approximately 101 4 negative‐U centers per cm2 except in the case of noble metals and Sn on GaSe(0001).
TL;DR: In this paper, the MBE growth of heteroepitaxial CdTe layers on (001)InSb using substrate temperatures, Ts, significantly higher than have been previously reported.
Abstract: As part of a program aimed at the growth of CdTe/InSb superlattices, a systematic study has been made of the MBE growth of heteroepitaxial CdTe layers on (001)InSb using substrate temperatures, Ts, significantly higher than have been previously reported. Using a modified two‐step growth technique, high quality layers have been successfully grown at temperatures as high as 310 °C with no evidence of either preferential Cd loss or CdTe/InSb interdiffusion. The new growth technique is described and cross‐sectional TEM and SIMS data from the grown layers is presented.
TL;DR: In this article, the surface morphology of Ga1−xAlxAs layers grown by molecular beam epitaxy (MBE) as a function of the layer parameters and the growth conditions was investigated.
Abstract: We report a detailed investigation of the surface morphology of Ga1−xAlxAs layers grown by molecular beam epitaxy (MBE) as a function of the layer parameters and the growth conditions. Under some conditions Ga1−xAlxAs layers exhibit a surface roughness characterized by a degradation of the in situ electron diffraction pattern and a very broad photoluminescence peak. The amplitude of the roughness, as observed by optical microscopy and measured by alphastep profiler, increases with the layer thickness, the growth rate r, and goes through a maximum for a substrate temperature TS≂650 °C, a flux ratio R=JV/JIII≂6 and an Al composition x≂0.5. However, smooth layers can be obtained using growth conditions like high TS (≥700 °C), low flux ratio (R≤2.5), or low growth rate (<0.5 μm/h). No surface roughness was observed for GaAs and AlAs layers. Moreover, a high concentration of foreign atoms at the surface of the growing layer (Sn dopant for example) yields to a quite perfect surface morphology. This paper also c...
TL;DR: In this paper, the authors present the implementation of the self-aligned TiSi2 process using rapid thermal processing to simultaneously fabricate transistor gates and junctions with a sheet resistance of 1 Ω/sq.
Abstract: This paper reviews recent progress towards integrating the self‐aligned titanium silicide process into VLSI NMOS and CMOS technologies, to simultaneously reduce the gate and junction sheet resistances to below 1 Ω/sq. In addition to reviewing the base line self‐aligned TiSi2 process, the key issues that must be addressed if the process is going to be successfully integrated into a VLSI process flow, without having adverse effects on device parameters, will be discussed. Such issues are how the sheet resistance can be reduced to <1 Ω/sq without bridging between the gate and source/drain regions, the effect of silicide stress on gate oxide integrity, and how both P‐ and N‐type junctions can be silicided without adversely affecting diode or transistor properties. Recent results on the hot electron hardness of silicided devices compared to unsilicided transistors will also be presented. The implementation of the self‐aligned titanium silicide process using rapid thermal processing to simultaneously fabricate transistor gates and junctions with a sheet resistance of 1 Ω/sq will also be described. Using the self‐aligned TiSi2 technology, fully functional VLSI CMOS and NMOS circuits of the 64K static random access memory class of complexity, with 1 μm gates, have been fabricated with yield that is similar to unsilicided parts.