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Nov 1986

Volume 4, Issue 6, pp. 1273-1471


Excimer laser photoablation of silicon

G. B. Shinn, F. Steigerwald, H. Stiegler, R. Sauerbrey, F. K. Tittel, and W. L. Wilson

J. Vac. Sci. Technol. B 4, 1273 (1986); http://dx.doi.org/10.1116/1.583505 (5 pages) | Cited 21 times

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The ultraviolet and visible emission spectra from excimer laser‐produced silicon plasmas were studied and the ablation rate measured as a function of laser energy density and wavelength. A spectroscopic investigation of the laser‐produced plasma showed Si i, Si ii, and Si iii spectral lines with higher laser intensity causing a higher degree of ionization in the plasma. Both time‐integrated and time‐resolved spectroscopic studies showed electronic transitions superimposed on a weak continuum over the entire range from 250 to 640 nm. The photoablation rate of Si was independent of laser wavelength (193 or 248 nm), and had an energy density threshold of ≊1.3 J/cm2. The threshold was almost independent of the buffer gas pressure between vacuum and 1000 Torr. These results are described in the framework recently developed for excimer laser ablation of metals.
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79.20.Ds Laser-beam impact phenomena
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Sputtering of SiO2 in a XeF2 and in a Cl2 atmosphere

D. J. Oostra, A. Haring, and A. E. de Vries

J. Vac. Sci. Technol. B 4, 1278 (1986); http://dx.doi.org/10.1116/1.583506 (5 pages) | Cited 25 times

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SiO2 has been bombarded by 3 keV Ar+ ions under simultaneous exposure to a thermal beam of Cl2 or XeF2. Mass spectra and time‐of‐flight distributions of the sputtered species have been measured. It is observed that during XeF2 exposure the sputtering yield of SiO2 is enhanced with a factor of 2.3. After ionizing the neutral ejected Si species, we have detected SiF+x (x=0–4) and SiOF+y ( y=0–2). The kinetic energy distributions of these particles indicate that the newly formed species have been bound loosely to the lattice and that they are sputtered predominantly by a collision cascade mechanism. The results are explained by assuming that adsorbed F atoms are mixed into subsurface layers in which Si–F bond formation takes place. Hardly any chemical enhancement of the sputtering yield of SiO2 is observed when Cl2 is added. In this case the Si species are detected as SiCl+x and SiOCl+y (x, y=0–2). The chlorine peak (Cl+) is an order of magnitude higher. The kinetic energy distribution of Cl shows that most of the chlorine is in the lattice chemically unbound. From the measurements it is concluded that the heat of formation determines that in the collision cascade Si–F bonds are formed while Si–Cl bonds are not. Differences in the enhancement of the sputtering yield between silicon and SiO2 can also be explained by differences in heat of formation.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Residue formation on Si surfaces in a CHF3 discharge environment

D. J. Vitkavage and T. M. Mayer

J. Vac. Sci. Technol. B 4, 1283 (1986); http://dx.doi.org/10.1116/1.583507 (9 pages) | Cited 7 times

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Ion beam simulation techniques are used to study fluorocarbon residue formation and substrate composition and structure modifications of silicon by CHF3 plasma environment. Fluorocarbon residues are shown to grow by direct ion incorporation or ion activated growth processes in ion beams over the energy range 50–1000 eV. At ion energy >150 eV concurrent sputtering of the overlayer film results in a steady state film thickness of ∼30 Å, relatively independent of ion energy. Films are fluorine deficient, with C/F ratio of 1–3 depending on ion energy, dose, and film thickness. Energetic ion (300 eV) penetration of the film results in continuous Si etching and substantial substrate modification. For 560 eV ion energy an ion‐mixed interfacial layer of approximately 25 Å thickness is produced which contains substantial O, C, and F. A deeper (>150 Å) damaged layer is observed due to H+ implantation. Removal of overlayer films and interfacial layers by standard cleaning procedures is addressed.
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81.65.-b Surface treatments
68.35.Dv Composition, segregation; defects and impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

The role of gas phase reactions, electron impact, and collisional energy transfer processes relevant to plasma etching of polysilicon with H2 and Cl2

Ole Krogh, Tom Wicker, and Brian Chapman

J. Vac. Sci. Technol. B 4, 1292 (1986); http://dx.doi.org/10.1116/1.583508 (9 pages) | Cited 6 times

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Plasma etching of silicon with H2 and Cl2 was simulated with mixtures of H2, Cl2, and SiCl4. The gas phase chemistry was elucidated by varying power and pressure. The cross sections for production of H (3p2P) atoms were probed through the emission response to pressure variations. Addition of rare gases to a hydrogen plasma identified qualitatively major energy transfer paths between the rare gas metastables and the H2/H system. We conclude that dissociation of hydrogen molecules and excitation of hydrogen atoms are separate electron impact collisional events that constitute the main excitation route in a hydrogen plasma. We find further that the role of metastable H atoms in the 2s2S state at 10.19 eV is minor, and that the direct dissociative excitation in a single electron impact at 16.57 eV is insignificant. The occurrence of state specific collisional energy exchange has limiting consequences for any actinometric method.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
52.75.-d Plasma devices
34.80.-i Electron and positron scattering

Auger electron spectroscopy sputter depth profiles on AlxGa1−xAs protected by As and GaAs ultrathin layers

P. Etienne, P. Alnot, J. F. Rochette, and J. Massies

J. Vac. Sci. Technol. B 4, 1301 (1986); http://dx.doi.org/10.1116/1.583509 (5 pages) | Cited 1 time

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The Auger electron spectroscopy sputter depth profiling technique has been used to evaluate the protective efficiency of ultrathin overlayers of As (∼25 Å) and GaAs (25 Å) against air exposure damaging effect of AlxGa1−xAs (x=0.3) epitaxial layers. It is shown that the As adsorbed overlayer is only partially effective to protect AlxGa1−xAs surface for a short air exposure. The surface of this reactive material can be more efficiently protected by GaAs, even for a very thin overlayer (25 Å). Results dealing with the effects of air and H2 annealings on the AlxGa1−xAs surface are also reported. They confirm the Ga segregation at the AlxGa1−xAs surface recently reported [Stall et al., J. Vac. Sci. Technol. B 3, 524 (1985) and Massies et al., ibid. 3, 613 (1985)].
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81.65.-b Surface treatments
68.55.Nq Composition and phase identification
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Fx Diffusion; interface formation

HgTe–CdTe superlattices grown on lattice‐mismatched GaAs substrates

M. L. Wroge, D. J. Leopold, J. M. Ballingall, D. J. Peterman, B. J. Morris, J. G. Broerman, F. A. Ponce, and G. B. Anderson

J. Vac. Sci. Technol. B 4, 1306 (1986); http://dx.doi.org/10.1116/1.583510 (4 pages) | Cited 5 times

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HgTe–CdTe superlattices were grown by molecular beam epitaxy on GaAs(100) substrates with CdTe buffer layers. The large (14.6%) lattice mismatch between CdTe and GaAs is relieved by a two‐dimensional array of misfit dislocations with a period of 3.1 nm. X‐ray diffraction, infrared transmittance, and Hall effect measurements are reported for thick (>5 μm) single crystalline superlattices.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
72.20.My Galvanomagnetic and other magnetotransport effects

An Auger electron spectroscopy, x‐ray photoelectron spectroscopy, secondary ion mass spectrometry and bulk analysis of pyrolytic boron nitride crucibles after vacuum baking

F. A. Chambers, G. W. Zajac, and T. H. Fleisch

J. Vac. Sci. Technol. B 4, 1310 (1986); http://dx.doi.org/10.1116/1.583511 (6 pages) | Cited 1 time

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The growth of high quality GaAs and AlGaAs using the molecular beam epitaxy (MBE) technique requires that all of the components of the system be kept very clean, especially the source materials (Ga, As, and Al), the crucibles, and the furnaces since they are at high temperatures during the growth of the material. The crucibles, made of pyrolytic boron nitride (PBN), are used after a cleaning procedure that consists of a 1 h heat treatment at 1600 °C in a vacuum of approximately 5×10−9 Torr or better. While this cleaning procedure has been used extensively, there have been no reported studies of the effectiveness of this procedure or its effect on the crucible. We have used mass spectrometry, AES, SIMS, XPS, and a modification of the LECO technique to study both baked and unbaked crucibles. In this paper we demonstrate that the cleaning procedure does remove impurities from the crucible, especially carbon. We also demonstrate that the cleaning procedure does not decompose the surface of the crucible as is commonly believed and that the recently observed dark striations on the interior of some of the crucibles after the bakeout are due to a physical restructuring of the surface and a possible local segregation of boron and not due to surface segregation of impurities such as carbon. We also present the first report of e‐beam induced decomposition of boron nitride.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Hx Electron impact: secondary emission
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Raman scattering study of plasma etching damage in GaAs

D. Kirillov, C. B. Cooper, and R. A. Powell

J. Vac. Sci. Technol. B 4, 1316 (1986); http://dx.doi.org/10.1116/1.583512 (3 pages) | Cited 5 times

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In the present work, we have applied Raman scattering to study the damage produced by etching GaAs with inert and reactive gas plasmas. (AIP)
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81.65.-b Surface treatments
78.30.Hv Other nonmetallic inorganics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.80.Jh Ion radiation effects

Deposition of polymer film patterns by ion beams

C. R. Fritzsche and K. Eisele

J. Vac. Sci. Technol. B 4, 1318 (1986); http://dx.doi.org/10.1116/1.583513 (3 pages)

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Abstract Unavailable
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology

Self‐aligned silicides or metals for very large scale integrated circuit applications

Shyam P. Murarka

J. Vac. Sci. Technol. B 4, 1325 (1986); http://dx.doi.org/10.1116/1.583514 (7 pages) | Cited 27 times

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The increases in the packing density and the resulting shrinkage of the silicon integrated circuit dimensions led to the investigation and successful application of the deposited refractory silicide layers as the gate and interconnection metallization. The continued shrinking of the device dimensions has now turned attention to further lowering of the resistance at the gate level and to finding a contact metallization for the shallow junctions. Although refractory metals are being considered for the former, self‐aligned silicides of cobalt, titanium, platinum, and nickel offer the possibility of satisfying both the gate and interconnection and contact metallization requirements. This paper will review the present status of the refractory silicide and refractory metal technologies and compare them with the upcoming self‐aligned silicide technology.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments
73.40.-c Electronic transport in interface structures

Properties of titanium silicide films deposited by plasma‐enhanced chemical vapor deposition

Diederik G. Hemmes

J. Vac. Sci. Technol. B 4, 1332 (1986); http://dx.doi.org/10.1116/1.583453 (4 pages)

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Titanium silicide is a desirable interconnect material for future very large scale integrated circuit (VLSI) devices because of its low resistivity (15 μΩ cm) and because of its low sinter temperature (600 °C) compared to other refractory metal silicides. Chemical vapor deposited (CVD) films have much better purity and step coverage than the conventional physical vapor deposited (PVD) films. A study has been made of titanium silicide deposited by plasma‐enhanced CVD (PECVD). Rutherford backscattering has been used to analyze the dependence of the as‐deposited film composition on the process parameters. The changes in the composition and the resistivity of the films during both furnace and rapid thermal anneals have been studied. It has been shown that it is possible to grow a SiO2 layer on top of the silicide film when a proper clean of the substrate surface is done before the deposition. Stress levels after anneal are about 1×1010 dyn/cm2. Anisotropic etch of the film is possible even when deposited on a polysilicon substrate.
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73.61.At Metal and metallic alloys
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification

Summary Abstract: Semiconducting silicides as potential materials for electro‐optic very large scale integrated circuit interconnects

M. C. Bost and J. E. Mahan

J. Vac. Sci. Technol. B 4, 1336 (1986); http://dx.doi.org/10.1116/1.583454 (3 pages) | Cited 14 times

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Abstract Unavailable
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.60.-q Optoelectronic devices
78.20.Jq Electro-optical effects
42.82.-m Integrated optics

Impurity effects in magnetron sputter deposited tungsten films

C. E. Wickersham, J. E. Poole, and K. E. Palmer

J. Vac. Sci. Technol. B 4, 1339 (1986); http://dx.doi.org/10.1116/1.583455 (5 pages) | Cited 2 times

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This paper describes the effect of metallic and nonmetallic impurities on the electrical and metallurgical properties of tungsten films sputter deposited onto oxidized silicon wafers. Tungsten films, 200‐nm‐thick, sputter deposited using a 99.996% pure tungsten target and a deposition rate of 6 nm/s with a substrate temperature of 400 °C had an as‐deposited resistivity of 13.5 μΩ cm. This value is within experimental error equal to the lowest values reported for electron‐beam evaporated and chemical vapor deposited films. Metallic impurities in the target increase the electrical resistivity of the tungsten films. Use of a 99.98% pure (3N8) tungsten target under identical conditions as those reported above produced films with resistivities of 17.3 μΩ cm or a 28% increase in resistivity due to an increase of less than 160 ppmw in the concentration of metallic impurities. Intentional addition of iron and copper to the tungsten film increased the film resistivity by factors of 5 and 1 nΩ cm/ppmw of impurity, respectively. Air leak rate into the sputtering chamber was also evaluated and found to significantly affect tungsten film resistivity. An air leak rate of 0.001 25  Torr 1/s increased the film resistivity from 16 to 21.8 μΩ cm or an average rate of 4640 μΩ cm/(Torr 1/s).
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73.61.At Metal and metallic alloys
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.40.Rs Electrical and magnetic properties related to treatment conditions

The formation of titanium silicide by arsenic ion beam mixing and rapid thermal annealing

R. K. Shukla, P. W. Davies, and B. M. Tracy

J. Vac. Sci. Technol. B 4, 1344 (1986); http://dx.doi.org/10.1116/1.583456 (8 pages) | Cited 2 times

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The reaction of titanium thin films with n+ doped single crystal silicon induced by As+ ion beam irradiation and subsequent rapid thermal annealing has been studied. Arsenic doping in the silicon substrate retards the thermal growth of silicide resulting in an incomplete conversion of the titanium into titanium disilicide during low temperature (∼600 °C) rapid thermal annealing under a nitrogen ambient. High energy As+ion beam irradiation (90–170 keV) prior to the rapid thermal annealing leads to intermixing of the titanium and silicon which, at sufficiently high energy and dosage, results in complete conversion of titanium to a silicide phase. Subsequent rapid thermal annealing of the ion beam irradiated samples induces further uptake of silicon into the silicide phase leading to the formation of the stable C‐54 titanium disilicide phase. However, very little additional titanium consumption occurs during the thermal annealing. The silicide formed by the ion beam mixing process shows superior sheet resistance uniformity and has a smoother morphology compared to thermally grown silicide. The uniformity of the silicidation reaction by ion beam mixing also leads to superior n+p junction characteristics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys

Titanium silicide formation by ion beam mixing and rapid thermal annealing

G. A. Mattiussi

J. Vac. Sci. Technol. B 4, 1352 (1986); http://dx.doi.org/10.1116/1.583457 (6 pages) | Cited 2 times

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The need for and use of ion beam mixing of metal silicides for very large scale integrated (VLSI) circuit technology is discussed in the form of a literature review and tutorial paper. Where possible, the formation of titanium disilicide (TiSi2) is discussed, although other metal silicides are considered. Throughout the paper, the relevance of ion beam mixing to the formation of devices is emphasized. In addition, the integration of this technique into a VLSI process flow is presented. It is concluded that for the technique of ion beam mixing to be considered for VLSI processing, research should be concentrated on micrometer‐sized features. In addition, ion beam mixing of Ti and SiO2 requires further investigation since the self‐aligned complementary metal‐oxide‐semiconductor (CMOS) process demands negligible interaction between these two materials. With this in mind, it is suggested that ion beam mixing of W and Mo silicides presents an easier target.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

A self‐aligned cobalt silicide technology using rapid thermal processing

L. Van den hove, R. Wolters, K. Maex, R. De Keersmaecker, and G. Declerck

J. Vac. Sci. Technol. B 4, 1358 (1986); http://dx.doi.org/10.1116/1.583458 (6 pages) | Cited 33 times

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The feasibility of a self‐aligned silicide technology based upon cobalt has been investigated. Silicidation reactions were performed by means of rapid thermal processing. Phase sequence, layer morphology, and reaction kinetics were studied by XRD, SEM, RBS, AES, and TEM. Extremely smooth, highly conductive (16 μΩ cm) CoSi2 films were formed by direct reaction of Co on Si, without significant lateral silicide formation at oxide edges. Shallow arsenic junctions were successfully silicided and low contact resistances were obtained on n+ and p+ Si.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

An advanced control system for semiconductor processing equipment

Ron Parker and Clark Fuhs

J. Vac. Sci. Technol. B 4, 1364 (1986); http://dx.doi.org/10.1116/1.583459 (5 pages)

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The move toward more sophisticated semiconductor processing equipment and the industry’s need for ‘‘turnkey’’ operation have put increased demands on the equipment control system and their architecture. There are different needs from four specific groups that must be addressed by today’s control systems. The process engineer should be provided with process flexibility to qualify the process; the system should be simple enough to easily transfer a process to manufacturing and the production fab operator; maintenance engineers need rich diagnostic functions incorporated into the software to provide routine diagnosis and maintenance; and the communication with the control hardware closes the loop, providing a high degree of safety. In addition, future factory automation will require communication from stand‐alone systems to host computers. A proven system control architecture has been developed to meet these needs. The control system described has special applications of both hardware and software, paying particular attention to the human needs.
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07.07.Tw Servo and control equipment; robots
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
89.20.Bb Industrial and technological research and development

Diffusion barrier properties of thin selective chemical vapor deposited tungsten films

B. W. Shen, G. C. Smith, J. M. Anthony, and R. J. Matyi

J. Vac. Sci. Technol. B 4, 1369 (1986); http://dx.doi.org/10.1116/1.583460 (8 pages) | Cited 9 times

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Diffusion barrier properties of selective chemical vapor deposited (CVD) tungsten to silicon and aluminum interdiffusion have been investigated using secondary ion mass spectroscopy, x‐ray diffraction analysis, and scanning electron microscopy. Samples of titanium layered pure aluminum on selective CVD tungsten on cleaned silicon wafers were prepared and sintered between 450 and 520 °C. The Ti layered aluminum was used to increase the capacity for silicon to facilitate the outdiffusion from the substrate. Magnetron sputter deposited Ti:W samples were also included in the analysis for comparison purposes. The experimental results indicated that 73 nm of selective tungsten with sheet resistance of 1.5 Ω/ was sufficient as a diffusion barrier for both aluminum and silicon at 450 °C for 30 min, but failed at 520 °C for 30 min. 33 nm thick selective tungsten with 7 Ω/ sheet resistance failed to prevent interdiffusion of aluminum and silicon even at 450 °C for 30 min. 100 nm of Ti:W remained an excellent diffusion barrier for anneals up to 485 °C for 30 min, but did not prevent Si outdiffusion at 520 °C, 30 min. No aluminum penetration was seen in Ti:W samples up to 520 °C. A ternary Ti–W silicide was identified at sintering temperatures as low as 485 °C. A possible formation mechanism is herein proposed.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.60.Wm Other nonelectronic physical properties

Properties of dc magnetron reactively sputtered TiN

Jim Stimmell

J. Vac. Sci. Technol. B 4, 1377 (1986); http://dx.doi.org/10.1116/1.583461 (6 pages) | Cited 2 times

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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.
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73.61.Ng Insulators
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments
81.15.Cd Deposition by sputtering

Comparison of low temperature and high temperature refractory metal/silicides self‐aligned gate on GaAs

S. P. Kwok

J. Vac. Sci. Technol. B 4, 1383 (1986); http://dx.doi.org/10.1116/1.583462 (9 pages) | Cited 8 times

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Since the first reported use of TiW gate as a stopping mask for n+ implantation for GaAs self‐aligned gate field effect transistors (SAGFET) in 1981, refractory metal compounds and silicides have found a widespread use in the GaAs SAGFET technology. However, the technique requires that the refractory metal (silicide)/GaAs interface be subjected to a high temperature postimplantation annealing, typically 750–900 °C. The mechanical, metallurgical, and most sensitively the electrical stabilities and reproducibility of the refractory metal (silicide)/GaAs Schottky barrier characteristics have become the major issues confronting the high temperature SAGFET technology. The use of a dielectric substitutional gate, which allows the refractory metal gate to be formed at a low temperature, typically room temperature to 400 °C, for fabrication of SAGFET was reported in 1983. With the advance of well controlled dry etching and photoresist planarization techniques, the low temperature SAGFET process becomes a potentially viable alternate technology. In this paper, comparisons of the two technologies and associated device performances are made. The basic issues of refractory metal/GaAs and dielectric/GaAs interface reactions, stress and impurity incorporation at high annealing temperatures are discussed.
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85.30.Tv Field effect devices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Characterization of reactively sputtered WNx film as a gate metal for self‐alignment GaAs metal–semiconductor field effect transistors

N. Uchitomi, M. Nagaoka, K. Shimada, T. Mizoguchi, and N. Toyoda

J. Vac. Sci. Technol. B 4, 1392 (1986); http://dx.doi.org/10.1116/1.583463 (6 pages) | Cited 19 times

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Properties of reactively sputtered WNx films on a GaAs substrate have been investigated by electrical and physical analyses. WNx films were deposited from a pure W target by using three types of sputtering systems: (1) Magnetron sputtering system equipped with rf and dc mode; (2) S‐gun sputtering system; (3) rf diode sputtering system. The composition of WNx films was easily and reproducibly controlled by changing the N2 content in Ar–N2 mixed ambient gas. The WNx–GaAs system was both electrically and metallurgically stable even after high‐temperature annealing of up to 800 °C. The Schottky barrier height to n‐type GaAs was more than 0.8 V, which is the highest value obtained so far among any other refractory metals. Self‐aligned GaAs MESFET’s were successfully fabricated using a WNx gate. The transconductance was typically 150 mS/mm for 1.5 μm gate length.
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68.55.Nq Composition and phase identification
85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering
73.40.Ns Metal-nonmetal contacts

Tungsten silicide Schottky contacts on GaAs

Zhu Zhongde, Nathan W. Cheung, Zachary J. Lemnios, Michael D. Strathman, and James B. Stimmell

J. Vac. Sci. Technol. B 4, 1398 (1986); http://dx.doi.org/10.1116/1.583464 (6 pages) | Cited 7 times

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Two types of I–V characteristics for W–Si/GaAs Schottky contacts have been observed. With sputtering deposition from a W–Si composite target (type A), The Schottky contacts have a Schottky barrier height ΦB of 0.64 V and an ideality factor, n of 1.05. The I–V behavior is independent of the WSix composition for x=0.42–2.3. With cosputtering from W and Si targets (type B), an excellent WSi0.6/GaAs Schottky contact is obtained with ΦB equal to 0.8 V and an ideality factor equal to unity. The I–V characteristics of both types of diodes agree with the theoretical thermionic‐emission model for both forward and reverse bias. For type B diodes, high‐temperature stability has been demonstrated with furnace annealing up to 750 °C. In previous studies, composition of the W–Si film has been emphasized as the single most important factor for GaAs Schottky gates. Our work has shown, besides silicide composition, surface cleaning procedures and silicide deposition techniques will have a greater effect on the diode I–V characteristics, the thermal stability of the Schottky contact, and the silicide adhesion on GaAs substrate. Sputter etching of the GaAs substrate prior to silicide deposition can improve the silicide adhesion up to a heat treatment of 1000 °C but with a degradation of diode performance. A negative substrate bias during deposition was shown to be a better compromise for both adhesion and electrical considerations.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Early stages in thin film metal–silicon and metal–SiO2 reactions under rapid thermal annealing conditions: The rapid thermal annealing/transmission electron microscopy technique

Menachem Natan

J. Vac. Sci. Technol. B 4, 1404 (1986); http://dx.doi.org/10.1116/1.583465 (5 pages) | Cited 3 times

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A simple and fast structural characterization technique for thin film solid‐phase reactions has been developed, based on a combination of rapid thermal annealing and transmission electron microscopy (the ‘‘RTA/TEM technique’’). The technique is used to investigate fast interfacial reactions in layered Si/Ni/Si, Si/Co/Si, Si/Ti/Si, and SiO2/Ti/SiO2 films. In contradiction to first‐phase rules, all three metal–Si systems exhibit nucleation of multiple ‘‘first’’ silicides; under certain conditions, an amorphous (metal+Si) mixture exists prior to this nucleation. The simultaneous study of Si–Ti and SiO2–Ti reactions with RTA/TEM can quickly determine processing ‘‘windows’’ when selective silicidation is required.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Diboride diffusion barriers in silicon and GaAs technology

J. R. Shappirio, J. J. Finnegan, and R. A. Lux

J. Vac. Sci. Technol. B 4, 1409 (1986); http://dx.doi.org/10.1116/1.583466 (7 pages) | Cited 4 times

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TiB2 and ZrB2 are members of the larger group of interstitial compounds which the transition metals form with boron, carbon, and nitrogen. Such materials are of significant interest for microelectronic application owing to a combination of low resistivity and outstanding diffusion barrier properties. We report here studies on the application of these diborides as diffusion barriers for both Si and GaAs based device technology. rf diode sputtered thin film ZrB2 has an annealed resistivity of 25 μΩ cm, rivaling that of its most widely employed silicide competitor, TiSi2 (18 μΩ cm). In addition, in experiments with bilevel structures consisting of first‐level ZrB2 and second‐level Al, no evidence of reaction has been observed in RBS spectra for samples heat treated in N2 at 625 °C for 2 h. These compounds thus appear to offer the prospect of serving the dual role of low resistivity contact metal as well as a self‐diffusion barrier in multilevel contact structures. Recent work on the application of these materials for GaAs contact technology is even more significant. Alloyed Ohmic contacts to n‐GaAs, a traditionally difficult technological problem, have been fabricated in which the Ohmic metallization (Ni/Ge/Au) in contact with the GaAs substrate is separated from the overlying thick Au upper contact by an intervening e‐beam deposited TiB2 layer. The resultant structure shows improved electrical stability on aging at 350 °C to those of a more conventional nature prepared similarly, but employing a Ni film in place of the TiB2. This improved stability is attributed to the effectiveness of the diboride as a diffusion barrier to the in‐migration of Au, thus preventing further modification of the Ohmic contact metallurgy obtained on alloying.
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68.35.Fx Diffusion; interface formation
73.61.Ng Insulators
73.40.Ns Metal-nonmetal contacts
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Recent trends in III–V strained layer research

G. C. Osbourn

J. Vac. Sci. Technol. B 4, 1423 (1986); http://dx.doi.org/10.1116/1.583467 (4 pages) | Cited 17 times

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Current directions in III–V strained layer superlattice research are briefly reviewed. Areas of recent emphasis include the study of the tailorable light hole mass values, the development of new III–V strained layer materials for infrared detector applications, and work on modulation‐doped field effect transistors employing strained quantum wells. Recent theoretical and experimental results as well as unresolved issues in these areas are discussed.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.30.Tv Field effect devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds

Recent developments in the strained layer epitaxy of germanium–silicon alloys

John C. Bean

J. Vac. Sci. Technol. B 4, 1427 (1986); http://dx.doi.org/10.1116/1.583468 (3 pages) | Cited 12 times

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This paper provides a brief review of recent work on strained layer GexSi1−x including modeling of critical thicknesses for single layers and superlattices; calculations and measurements on strain induced alteration of alloy band gap and heterostructure band alignment; and application to modulation‐doped field effect transistors (MODFET) and 1.3 μm photodetector devices.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
85.30.Tv Field effect devices
85.60.Gz Photodetectors (including infrared and CCD detectors)

Interface defects and disorder in a‐Si:H/a‐SiNx:H superlattices

C. B. Roxlo, B. Abeles, and P. D. Persans

J. Vac. Sci. Technol. B 4, 1430 (1986); http://dx.doi.org/10.1116/1.583469 (5 pages) | Cited 3 times

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We have examined the interfaces in amorphous silicon hydride/amorphous silicon nitride multilayers with layer thicknesses varying from 7 to 200 Å. Infrared measurements show that these interfaces are heavily hydrogenated, with 1015 cm−2 excess hydrogen atoms per interface pair. Electroabsorption spectroscopy indicates that the interfaces are charged and asymmetrical, indicating that the interface properties depend upon the order of deposition. We attribute these effects to interface defects which are induced by the severe mismatch in bond density at the interface. Raman measurements show that the interface region is highly disordered, with bond angle fluctuations of 13°. Effects due to the interface region extend 10–20 Å into the a‐Si:H layers.
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68.35.Dv Composition, segregation; defects and impurities
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.20.Ck Nonmetals

Expitaxial metal–semiconductor structures and their properties

R. T. Tung, A. F. J. Levi, and J. M. Gibson

J. Vac. Sci. Technol. B 4, 1435 (1986); http://dx.doi.org/10.1116/1.583470 (9 pages) | Cited 14 times

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Recent development of epitaxial silicide technology has allowed structurally perfect metal–semiconductor interfaces to be fabricated. The atomic structure at these abrupt silicide–silicon interfaces has been modeled and electron transport across Schottky barriers with homogeneous interface structure have been studied for the first time. In addition, high quality multilayered structures of epitaxial metals and semiconductors have been fabricated, opening up possibilities for very high speed device applications. This paper reviews the state‐of‐the‐art growth techniques, and the novel structures and properties of single crystal silicide thin films and multilayers.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of strain on the elastic properties of superlattices

Ivan K. Schuller and M. Grimsditch

J. Vac. Sci. Technol. B 4, 1444 (1986); http://dx.doi.org/10.1116/1.583471 (3 pages) | Cited 7 times

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The elastic properties of superlattices are strongly affected by strains in these materials. Elastic anomalies have been found in Nb/Cu, Mo/Ni, V/Ni, and Au/Cr superlattices. The strains measured with x rays explain quantitatively the elastic softening in Mo/Ni. An extension of these arguments explains not only the softening of Nb/Cu but the hardening and softening observed in Au/Cr. The origin of the strains is not known at the present time.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness

Mechanical properties and diffusion of metallic superlattices

T. Tsakalakos

J. Vac. Sci. Technol. B 4, 1447 (1986); http://dx.doi.org/10.1116/1.583472 (11 pages)

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An enhanced modulus effect has been observed in several composition modulated thin films systems containing short wavelength modulations 0.8–1.0 nm. The foils were produced by vapor deposition using two or three source evaporators. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase (up to 300%) in modulus. The plastic behavior, breaking and microhardness of these foils are also presented as a function of the modulation parameters. Current theories based on electronic and strain effects on the elastic constants of metals are also presented to explain the origin of the supermodulus effect. Interdiffusivities of binary and ternary modulated alloys have been measured from the decay of the x‐ray diffraction satellite intensities produced by the modulation. The stability of concentration waves at various temperatures is also discussed and examples of the determination of spinodal temperatures are given. The effect of loss of coherency and the appearance of screening singularities in the diffusivities are also considered.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Fx Diffusion; interface formation
68.60.Bs Mechanical and acoustical properties
68.35.Gy Mechanical properties; surface strains

The effects of elastic relaxation on transmission electron microscopy studies of thinned composition‐modulated materials

M. M. J. Treacy and J. M. Gibson

J. Vac. Sci. Technol. B 4, 1458 (1986); http://dx.doi.org/10.1116/1.583473 (9 pages) | Cited 39 times

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Composition modulations in defect‐free crystalline materials are generally accompanied by a lattice distortion where unit cell dimensions are not characteristic of the local composition. The distortion originates from the constraint that the interatomic spacings perpendicular to the modulation direction be commensurate from one layer to the next. Thus there is an internal stress field set up in the material which attempts to suppress unit cell expansions and contractions in these perpendicular directions. A well‐known example is the tetragonal distortion observed in bulk, cubic strained layer superlattices, and spinodally decomposed alloys. However, it is frequently overlooked that these stresses can be significantly relaxed near surfaces of the bulk material, particularly those surfaces lying perpendicular to the modulation direction. This relaxation can be a dominating effect in materials which have been thinned in cross section for study by TEM. Lattice plane bending near the specimen surfaces can cause strong diffraction contrasts, and the local lattice spacings are representative of neither the bulk, tetragonally distorted material, nor the unstressed material. In this paper we discuss how this important, and oft‐neglected relaxation affects TEM bright‐field and dark‐field image contrasts, high resolution lattice images, and interpretation of selected area diffraction data. We also derive expressions, relevant for all sample thicknesses, describing the relaxation strain field in cubic anisotropic materials, thinned perpendicularly to the modulation direction. The results are discussed in the context of two classes of modulated materials, namely spinodally‐decomposed InGaAsP alloys and GeSi/Si strained layer superlattices.
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07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Application of x‐ray topographic methods to thin film electronic materials

Sigmund Weissmann

J. Vac. Sci. Technol. B 4, 1467 (1986); http://dx.doi.org/10.1116/1.583474 (5 pages)

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X‐ray methods are presented which, besides offering a topographic survey of the defect structure in electronic materials, give quantitative information on the induced strain distribution. Complete strain tensor analyses are obtained by the back‐reflection divergent beam method and by the method of computer‐aided rocking curve analysis (CARCA). The latter is based on the double‐crystal diffractometer principle. An example of the strain analysis by CARCA is given showing the strain dependence on the thickness variation of an InGaAsP film grown on a substrate of InP. Valuable information on the density of interface dislocation is obtained by combining these methods with lattice curvature measurements using scanning topography with automatic Bragg angle control. The elucidation of the strain distribution in depth becomes enhanced by application of x radiation of various wavelengths.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Dv Composition, segregation; defects and impurities
68.55.-a Thin film structure and morphology
85.60.-q Optoelectronic devices
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