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Nov 1987

Volume 5, Issue 6, pp. 1547-1759


Pressure dependence of the growth of polycrystalline silicon by low‐pressure chemical‐vapor deposition

D. Meakin, K. Papadopoulou, S. Friligkos, J. Stoemenos, P. Migliorato, and N. A. Economou

J. Vac. Sci. Technol. B 5, 1547 (1987); http://dx.doi.org/10.1116/1.583671 (4 pages) | Cited 9 times

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The growth of polycrystalline silicon at temperatures below 640 °C by the pyrolysis of silane at very low pressures (<40 mTorr) was found to be activated with an activation energy depending on the pressure. Two modes of growth were observed: columnar and twinned, below and above 10 mTorr, respectively. The rate of growth for both types is only slightly dependent on the pressure. The columnar growth is associated with an increase of the activation energy, while the change to the twinned structure is associated with a drop in the activation energy to almost zero from where it increases with pressure. The influence of the flow mode is also discussed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Silicon epitaxy on germanium using a SiH4 low‐pressure chemical‐vapor deposition process

Kiyohisa Fujinaga, Yasuo Takahashi, Hiromu Ishii, Izumi Kawashima, and Shoh‐ichi Hirota

J. Vac. Sci. Technol. B 5, 1551 (1987); http://dx.doi.org/10.1116/1.583672 (4 pages) | Cited 1 time

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This work describes a process of Si epitaxy on a (100)Ge surface using a SiH4–H2 gas low‐pressure chemical‐vapor deposition (LPCVD) system. Germanium epitaxial film formed on (100)Si wafers using GeH4–H2 gas in a LPCVD reactor was used as the experimental substrates. It was found that Si grew epitaxially through a SiH4 thermal decomposition reaction on the clean Ge surface within a growth temperature range of 650 to 730 °C. By contrast, (110)‐oriented polycrystalline Si grew at a higher temperature of 790 °C. It was clarified that the reason for this polycrystalline Si growth at 790 °C was that the Si epitaxy was disturbed by the Si oxide layer which forms immediately on the Ge surface through susceptor‐induced SiO in the LPCVD reactor.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low‐pressure deposition of high‐quality SiO2 films by pyrolysis of tetraethylorthosilicate

F. S. Becker, D. Pawlik, H. Anzinger, and A. Spitzer

J. Vac. Sci. Technol. B 5, 1555 (1987); http://dx.doi.org/10.1116/1.583673 (9 pages) | Cited 24 times

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The deposition of SiO2 by pyrolysis of tetraethylorthosilicate (TEOS) at pressures below 1 Torr was investigated at temperatures between 650 and 800 °C. We found oxide thickness variations of <±5% for suitable process conditions (PD ≤500 mTorr, wafer spacing ≥4.7 mm, TD <730 °C, deposition rate 16 nm min−1). Tests with 150‐mm wafers showed that uniformities of ±2% can be achieved if the wafer spacing is increased to 10 mm. Raising the deposition pressure improves the step coverage in deep trenches but degrades the thickness uniformity across the wafer. The investigations of etch rates in different media show strong dependences on the anneal temperature for etchants containing HF but only a slight dependence for plasma etching. The dielectric breakdown strength of the oxides was 8 MV cm−1 and the failure rate after 500‐ms current stress at 1 mA cm−2 lower than 20%. We found values for the interface state density of 1×1010 eV−1 cm−2 and for the oxide charge density in the range 3×1010 cm−2 to 2.5×1011 cm−2, depending on the oxide thickness. The hysteresis of C–V scans was <2 mV. No substantial shift of the C–V curve was found after temperature–bias stress. Our I–V investigations showed that the carrier transport is governed by the Poole–Frenkel mechanism. These results as well as secondary ion mass spectroscopy investigations of the layers confirm that Merck TEOS can be used to grow oxide films of sufficient electrical quality for microelectronic applications.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.55.-a Thin film structure and morphology
81.05.Kf Glasses (including metallic glasses)
81.65.-b Surface treatments

Unique very low temperature plasma‐enhanced chemical‐vapor deposition glass process for hot and cold wall commercial reactors

R. H. Dorrance, K. E. Schoenberg, and T. A. Streif

J. Vac. Sci. Technol. B 5, 1564 (1987); http://dx.doi.org/10.1116/1.583674 (5 pages) | Cited 1 time

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High‐quality glass and phosphosilicate glass films have been deposited as low as 165 °C in hot and cold wall plasma‐enhanced chemical‐vapor deposition (PECVD) commercial reactors. The dependence of hydrogen incorporation, chemical stability in buffered oxide etch, and the inducement of hillock growth in underlying Al films upon the deposition conditions have been investigated. In both hot and cold wall commercial reactors a unique process has been developed at 165 °C to deposit glass films which exhibit properties not unlike PECVD glass deposited at 380 °C. Hillock growth induced in Al films during glass deposition is eliminated at 165 °C. Deposition rate, uniformity, etch rate, refractive index, particle and pinhole density, and film stress are reported.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Kf Glasses (including metallic glasses)
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
78.66.Jg Amorphous semiconductors; glasses

Characteristics of Nb‐based tunnel junctions fabricated by selective trilayer ion‐beam etching process

H. Tsuge

J. Vac. Sci. Technol. B 5, 1569 (1987); http://dx.doi.org/10.1116/1.583675 (6 pages)

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Characteristics of Nb/Nb oxide/Pb‐alloy junctions fabricated by selective trilayer ion‐beam etching process have been studied with respect to junction quality, reproducibility, uniformity, and thermal stability. The key steps in the process comprise in situ junction trilayer formation involving thermal oxidation, junction area definition by deep ultraviolet photolithography, and highly selective Pb‐alloy layer patterning by ion‐beam etching in an Ar–O2 atmosphere. Especially, the junctions fabricated in this process have exhibited excellent uniformity and reproducibility with PbAuIn and PbIn counterelectrodes. Standard deviations in critical current for 100 series‐connected junctions with 4×4 and 2×2 μm areas are 0.8% and 2.4%, respectively. The junctions with critical currents of about 80% of Bardeen–Cooper–Schrieffer values and without any knee structure in I–V curves are obtained reproducibly over a wide critical current range from 102 to 104 A/cm2. Annealing tests have indicated that these junctions have sufficient thermal stability for integrated circuits.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling
73.40.Rw Metal-insulator-metal structures
81.65.-b Surface treatments

Properties of a laser‐plasma x‐ray source for x‐ray lithography

E. A. Crawford, A. L. Hoffman, G. F. Albrecht, and M. R. Sogard

J. Vac. Sci. Technol. B 5, 1575 (1987); http://dx.doi.org/10.1116/1.583676 (13 pages) | Cited 3 times

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We have used an advanced, near diffraction limited Nd:YAG laser, operated at 1.06 μm and employing a zig‐zag slab amplifier, to generate x rays from the laser induced plasmas of a number of target materials. The x‐ray conversion efficiencies were studied as a function of target material and laser parameters. We have measured the x‐ray spectra, for x‐ray energies above about 1 keV, and used them to evaluate this source with regard to x‐ray lithography. A number of target material, resist, and mask combinations appear suitable for a lithography system capable of 0.25‐μm minimum feature size.
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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.)
07.85.-m X- and γ-ray instruments
81.65.-b Surface treatments

Ultimate resolution and contrast in ion‐beam lithography

M. D. Giles, R. K. Watts, and E. Labate

J. Vac. Sci. Technol. B 5, 1588 (1987); http://dx.doi.org/10.1116/1.583677 (3 pages)

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Ion‐beam lithography with a stencil mask is capable of very high resolution. We quantify the resolution by calculating the modulation transfer function for protons of energies suitable for patterning resist of useful thickness.
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81.65.-b Surface treatments
07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Reactive ion etching of GaAs with high aspect ratios with Cl2–CH4–H2–Ar mixtures

N. Vodjdani and P. Parrens

J. Vac. Sci. Technol. B 5, 1591 (1987); http://dx.doi.org/10.1116/1.583634 (8 pages) | Cited 6 times

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A new process for RIE of GaAs employing Cl2–CH4–H2–Ar etching gases is presented. The effect of CH4 and H2 on etch rate, etch profile, and surface morphology is studied. The plasma excited species are monitored in situ by emission spectroscopy and etch depths measured by laser interferometry. Anisotropic profiles and residue‐free surfaces are obtained with Cl2–CH4–H2–Ar and Cl2–CH4–H2–Ar gases. Depending on process parameters, selectivities up to 180 with respect to SiO2 are obtained allowing deep etching. X‐ray photoelectron spectroscopy and Auger electron spectroscopy of different etched surfaces are compared with a chemically etched reference surface. This shows that a Cl2/H2/Ar etch leaves the surfaces, contamination free.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Gallium arsenide and aluminum gallium arsenide reactive ion etching in boron trichloride/argon mixtures

A. Scherer, H. G. Craighead, and E. D. Beebe

J. Vac. Sci. Technol. B 5, 1599 (1987); http://dx.doi.org/10.1116/1.583635 (7 pages) | Cited 11 times

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GaAs and Al0.3Ga0.7As were reactive ion etched in a mixture of boron trichloride and argon. The effects of the independent variables such as the time, power, pressure, and gas composition on the etch depth as well as the quality of the resulting etched surfaces were analyzed through a multiple linear regression approach. This provided second‐order equations with an excellent ability to describe experimental results. The etching conditions for GaAs and AlGaAs were compared and optimum parameters for equal rate etching of GaAs/Al0.3Ga0.7As layers with straight walls were obtained. These were then sucessfully applied to the high‐resolution structuring of multiple quantum well layers, and structures as small as 40 nm were etched. The addition of oxygen to the etch gas produced a high‐quality etch for GaAs with >5:1 rate selectivity over Al0.3Ga0.7As.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Dry etching of via connections for GaAs monolithic microwave integrated circuits fabrication

S. Salimian, C. B. Cooper, and M. E. Day

J. Vac. Sci. Technol. B 5, 1606 (1987); http://dx.doi.org/10.1116/1.583636 (5 pages) | Cited 14 times

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Through‐the‐wafer low‐impedance via connections can improve characteristics of GaAs monolithic microwave integrated circuits (MMICs). A reactive ion etch process has been developed to etch via holes through 100‐μm‐thick substrates using SiCl4/Cl2 mixtures in a single‐wafer, load‐locked reactive ion etcher. The process satisfies the requirements of the via etch with regard to anisotropy, selectivity, profile, and surface morphology. In addition, the single‐wafer system has low‐overhead cycle times and a wide‐process latitude. This process was used to fabricate a MMIC distributed amplifier with significant improvements in gain performance.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.-b Surface treatments
85.30.De Semiconductor-device characterization, design, and modeling
84.30.Le Amplifiers

Cavernous undercuts appearing in reactive ion etched submicron‐wide deep trenches

Shigehisa Ohki, Masatoshi Oda, Hideo Akiya, and Toshitaka Shibata

J. Vac. Sci. Technol. B 5, 1611 (1987); http://dx.doi.org/10.1116/1.583637 (6 pages) | Cited 16 times

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The mechanism for the cavernous undercuts appearing on submicron‐wide Si trench sidewalls etched in Cl2 plasma is investigated. Etching with the inclined Si substrate implies that the ions scattered from the opposing mask edge plane are responsible for the undercut. Angular and energy distributions of ions scattered from the mask edges are simulated with a Monte Carlo method. The number and energies of the scattered ions are calculated as being high enough to etch sidewalls. Etching profile simulation incorporating the ion scattering effect shows good agreement with experimental results concerning the amount and the location of the undercut. These results apparently show that ion scattering at a sloped mask edge is the dominant origin of the cavernous undercut.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.40.Hf Plasma-material interactions; boundary layer effects

An x‐ray photoelectron spectroscopy study of sulfur hexafluoride etchant residue on silicon and silicon dioxide

J. H. Thomas and L. H. Hammer

J. Vac. Sci. Technol. B 5, 1617 (1987); http://dx.doi.org/10.1116/1.583638 (5 pages) | Cited 5 times

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X‐ray photoelectron spectroscopy has been used to characterize sulfur hexafluoride radio frequency (rf) plasma exposure in a reactive ion configuration. Reactive ion etched silicon is coated with a thin layer of SiFx similar to that observed on CF4 reactive ion etched silicon. A similar thin layer is observed on SiO2. When the surface is inadvertently contaminated (in this instance with nickel), sulfur, not observed on a clean surface, is present. In addition, silicon becomes roughened. Dilution of SF6 in argon gas does not significantly change the surface residue chemistry but does greatly decrease the etch rate of silicon. Increasing the power density from 0.2 to 1.2 W/cm2 increases the etch rate by a factor of ∼20. At the highest power densities, surface contamination is observed in the form of nickel and sulfur residues. Finally, as in the case of CF4 reactive ion etched silicon, the surface is observed to be crystalline at the lower power densities due to lack of ion bombardment damage effects and becomes amorphous as the power density is increased. At an equivalent power density, the self‐bias generated in an SF6 plasma was measured to be significantly less than that in a CF4 plasma. High silicon etch rates are achieved at very low power densities as compared with CF4 reactive ion etching confirming the findings reported in literature references. This study leads to the conclusion that CF4 may be a better etchant system than SF6 for contact cleaning.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments
81.05.Kf Glasses (including metallic glasses)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Photoemission studies of AlAs–GaAs alloys, heterostructures, and superlattices

H. Okumura, I. Yoshida, S. Misawa, and S. Yoshida

J. Vac. Sci. Technol. B 5, 1622 (1987); http://dx.doi.org/10.1116/1.583639 (6 pages) | Cited 1 time

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Inner core levels and valence‐band structures of molecular‐beam epitaxy‐grown AlxGa1−xAs alloys, AlAs/GaAs heterostructures and [(AlAs)2(GaAs)2]n superlattices were investigated by photoemission measurements. The variations in accordance with the structures were observed for the valence bands, while the binding energies of inner core levels of all the structures are constant within ±0.1 eV. The minimum layer thickness of GaAs or AlAs necessary to show its peculiar band structure was found to be 5∼6 monolayers. The valence‐band offset between AlAs and GaAs was estimated to be 0.12±0.33 eV. The spectra for the valence bands of superlattices showed the different features from those of GaAs, AlAs, and AlGaAs alloys.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds
81.65.-b Surface treatments

An electrohydrostatic analysis of equilibrium shape and stability of stressed conducting fluids: Application to liquid metal ion sources

M. Chung, N. M. Miskovsky, Paul H. Cutler, T. E. Feuchtwang, and E. Kazes

J. Vac. Sci. Technol. B 5, 1628 (1987); http://dx.doi.org/10.1116/1.583640 (11 pages) | Cited 3 times

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An exact mathematical treatment of the problem of an electrically stressed fluid from zero field to the onset of instability gives rise to the nonlinear electrohydrodynamic equations which, in general, are not amenable to analytic solution. To make the problem more tractable, one considers two limiting regimes, the electrohydrostatic (EHS) and the electrohydrodynamic (EHD) limits. In the EHS case, the fields and the velocities are assumed to be small so that quasistatic equilibrium exists and the fluid surface is essentially at rest. In this paper we consider the electrohydrostatic analysis of the equilibrium shape and stability of the electrically stressed fluids. The current work reintroduces the EHS stability criterion due to Zeleny, as well as a new set of equations and numerical procedure for analyzing the stability of an axially symmetric fluid with an arbitrary shaped surface. These are contrasted with a stability criterion, introduced by Taylor, which it is argued, is only an equilibrium condition and not a proper criterion for analyzing the general stability of electrified fluids. The Taylor and Zeleny criteria are applied to fluid sources modeled as simple coordinate surfaces, such as the cone, the cusp, and the hyperboloid. These results lead to a new physical interpretation of the onset of fluid instability in the EHS limit. A set of partial differential equations is derived, whose solution describes the equilibrium shape of a conducting fluid as a function of the applied electric field. Numerical results are presented for the evolution of the equilibrium shapes of several liquid metals as a function of the applied voltage. Values of the critical or breakdown voltage are obtained from these results and found to be in good agreement with experiment. Finally, the EHS analysis indicates that a realistic and accurate treatment of the onset of instability requires fluid flow in a dynamical model.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A process dependent study of Al/Si/Cu very large scale integration metallization. I. Spectroscopic properties

C. Hong, R. L. Hance, and R. E. Pyle

J. Vac. Sci. Technol. B 5, 1639 (1987); http://dx.doi.org/10.1116/1.583641 (5 pages)

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Spectroscopic characterization of samples of sputter‐deposited Al/Si/Cu very large scale integration metallization 1.3 μ thick having 1 wt. % Si and 0.0, 0.2, 0.4, and 0.8 wt. % Cu with and without a forming gas (N2/H2) 450 °C anneal for 1 h was performed as a function of deposition temperatures of 100, 163, 263, 363, and 463 °C. Secondary ion mass spectroscopic depth profiles of the metallization samples show a unique redistribution of the Si from the bulk to the metal/oxide interface at deposition temperatures between 263 and 363 °C. These data are correlated with scanning electron microscope micrographs of Si module precipitation on the silicon dioxide substrate surface after removal of the Al by an Al‐specific wet etch. In a subsequent paper, electrical and mechanical characterization results of these same metallization samples will be reported from resistivity and Knoop hardness measurements.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology

Schottky barrier formation of various metals on n‐GaAs (100) by electrochemical deposition

P. Allongue and E. Souteyrand

J. Vac. Sci. Technol. B 5, 1644 (1987); http://dx.doi.org/10.1116/1.583642 (6 pages) | Cited 11 times

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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.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Boron contamination of in situ heated silicon surfaces

A. Casel, E. Kasper, H. Kibbel, and E. Sasse

J. Vac. Sci. Technol. B 5, 1650 (1987); http://dx.doi.org/10.1116/1.583643 (4 pages) | Cited 9 times

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Interfacial  p doping due to B contamination is routinely detected in Si molecular‐beam epitaxy (MBE) when using standard MBE cleaning schemes. The influence of the wet chemical precleaning as well as of the in situ cleaning is investigated with respect to this effect: whenever chemical precleaning results in a hydrophilic Si surface, interfacial  p‐type doping due to B contamination of 1012 cm−2 is detected, whereas for hydrophobic Si surfaces the B contamination is reduced by a factor of about 50. Concerning the in situ cleaning, a reduction of the preheating temperature TH correlates with a decrease of  p‐type doping for hydrophilic cleaned samples, though the chemical B contamination is independent of TH, i.e., the in situ preheating induces an electrical activation of the B contamination.
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81.65.-b Surface treatments
68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Transitions in the reflection high‐energy electron‐diffraction pattern as a substrate temperature probe in molecular‐beam epitaxy

L. P. Ramberg, J. Westin, and T. G. Andersson

J. Vac. Sci. Technol. B 5, 1654 (1987); http://dx.doi.org/10.1116/1.583644 (2 pages) | Cited 8 times

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In molecular‐beam epitaxy systems, a substrate reference temperature can be established from observations of transitions in the reflection high‐energy electron‐diffraction pattern. For GaAs, we present the temperature for one such transition as a function of arsenic background pressure.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.55.-a Thin film structure and morphology

Erratum: Summary Abstract: Reflection high‐energy electron diffraction measurements of AlGaAs growth instabilities and roughening rates of misoriented substrates [J. Vac. Sci. Technol. B 5, 710 (1987)]

D. Saluja, P. R. Pukite, S. Batra, and P. I. Cohen

J. Vac. Sci. Technol. B 5, 1656 (1987); http://dx.doi.org/10.1116/1.583645 (1 page)

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Abstract Unavailable
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Gy Mechanical properties; surface strains
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
99.10.Cd Errata

Nucleation and growth of chemically vapor deposited tungsten on various substrate materials: A review

Eliot K. Broadbent

J. Vac. Sci. Technol. B 5, 1661 (1987); http://dx.doi.org/10.1116/1.583646 (6 pages) | Cited 8 times

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W films produced by chemical‐vapor deposition (CVD), typically via reduction of WF6, are being used for numerous applications in very large scale integrated circuit technology. Blanket and selectively deposited films require nucleation and growth on a specific underlayer material—Si, metal, or metal silicide. The compatibility of CVD W with various underlayers is reviewed for the device applications of contact/via fill, diffusion barrier, metal interconnect, and source/drain coating. Nucleation of W directly on single crystal Si can sometimes produce tunnel‐defect structures at the edges or along the entire interface of the deposit. Sputtered Mo and W, and to some extent TiW and TiN, have been shown to be suitable nucleation layers for CVD W, yielding a fluorine‐free interface with low‐electrical contact resistance. A sputtered W/Ti adhesion bilayer is demonstrated for a blanket W deposition+etchback process. CoSi2 appears an appropriate choice where CVD W and salicide technologies are combined.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Cg Contact resistance, contact potential
68.35.Dv Composition, segregation; defects and impurities

Self‐aligned titanium silicide device technology by NH3 plasma assisted thermal annealing

Bing‐Zong Li, Shi‐Fang Zhou, Jia Li, and Ting‐Ao Tang

J. Vac. Sci. Technol. B 5, 1667 (1987); http://dx.doi.org/10.1116/1.583647 (7 pages) | Cited 3 times

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The self‐aligned titanium silicide device technology has been studied by using NH3 plasma assisted thermal annealing and ion implant through titanium metal or silicide film. Enhanced surface nitridation of titanium by activated species suppresses lateral silicide growth and oxide contamination. NH3 plasma assisted annealing can be used as an effective method to form TiSi2 and activate implanted dopant. P+N junction and P channel metal–oxide–semiconductor field‐effect transistor can be produced by boron implant through Ti metal or its silicide and the NH3 plasma assisted thermal annealing.
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81.65.-b Surface treatments
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.30.Tv Field effect devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Dopant redistribution in silicide–silicon and silicide–polycrystalline silicon bilayered structures

S. P. Murarka and D. S. Williams

J. Vac. Sci. Technol. B 5, 1674 (1987); http://dx.doi.org/10.1116/1.583648 (15 pages) | Cited 18 times

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Dopants in any layer of the silicide–silicon or silicide–polycrystalline silicon bilayer structures are found to distribute readily throughout the bilayer affecting the electrical and the mechanical properties of the composite. In this paper the phenomenon of dopant redistribution in such structures is reviewed. The factors that influence the redistribution processes are (a) the diffusivity of dopants in the structure; (b) the solid solubility of dopants in the silicide and in the silicon; (c) the segregation coefficient of dopant at the surface and at the interfaces, and (d) the evaporative or the reactive losses of dopant to the heat‐treating environment. Each of these factors is discussed. The available experimental results are reviewed in view of these considerations. It is shown that there are a large number of variables and that the available experimental results only provide a technological base for the use of dopants in the structures studied. To obtain a fundamental understanding of the process that determines the dopant redistribution, more carefully planned experiments will be necessary.
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68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities

Titanium silicide growth by rapid‐thermal processing of Ti films deposited on lightly doped and heavily doped silicon substrates

N. de Lanerolle, D. Hoffman, and D. Ma

J. Vac. Sci. Technol. B 5, 1689 (1987); http://dx.doi.org/10.1116/1.583649 (7 pages) | Cited 3 times

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A series of experiments were conducted to obtain a better understanding of the titanium silicide growth on lightly doped and heavily boron and arsenic implanted single‐crystal (100) p‐type silicon, as well as on lightly doped and heavily phosphorus diffused polycrystalline silicon. Experiments were carried out under argon and nitrogen ambients using a two‐step annealing process with a rapid‐thermal processor (RTP). The growth kinetics in the RTP are compared for different ambients, times, and temperatures of annealing and various initial titanium thicknesses. Data will be presented which show that the type and amount of doping have a significant impact on the growth kinetics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
73.61.At Metal and metallic alloys

The importance of the short‐circuit failure mode in aluminum electromigration

Janet M. Towner

J. Vac. Sci. Technol. B 5, 1696 (1987); http://dx.doi.org/10.1116/1.583650 (5 pages)

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Electromigration was studied in a number of Al‐based metallizations. For pure Al and Al–Cu alloys, open circuits were the dominant failure mode. In other systems, including layered conductors and homogeneous Al–Ti, Al–Cr, and Al–V alloys, interlevel short‐circuit failure was greatly favored. Short circuits were usually detected prior to a significant increase in the conductor resistance.
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66.30.Qa Electromigration
73.61.At Metal and metallic alloys

TiW nitride thermally stable Schottky contacts to GaAs: Characterization and application to self‐aligned gate field‐effect transistor fabrication

A. E. Geissberger, R. A. Sadler, M. L. Balzan, and J. W. Crites

J. Vac. Sci. Technol. B 5, 1701 (1987); http://dx.doi.org/10.1116/1.583651 (6 pages) | Cited 9 times

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The thin‐film properties and temperature stability of titanium–tungsten nitride (TiWNx) Schottky contacts to GaAs have been investigated as a function of x, the atomic percent of nitrogen in the film. A Ti30W70 composite target was reactively sputtered onto GaAs substrates in nitrogen using argon as the diluent gas. The partial pressure of nitrogen was varied from 0% to 100%. This resulted in x varying from 0 to 27 at. %; however, the films contained a constant Ti–W atomic ratio of 0.18, regardless of x. The film stress and resistivity were well‐behaved and reproducible functions of x. Schottky contact characteristics were measured after annealing at several temperatures. After an 810 °C furnace anneal, the ideality factor (n) and barrier height (ϕB) displayed well‐defined, broad extrema as a function of x. Both the best average values of n and ϕB and their smallest standard deviations occurred for x=10 at. % of nitrogen. Thus the most stable and uniform TiWNx–GaAs Schottky contact was obtained from TiWN10. TiWN10 has been used as the refractory metal in ITT’s self‐aligned gate digital GaAs integrated circuit process to obtain gate delays as low as 19 ps at a power‐delay product per gate of 19 fJ.
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68.60.Dv Thermal stability; thermal effects
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices

High‐temperature stable W/GaAs interface and application to metal–semiconductor field‐effect transistors and digital circuits

Jack Y. Josefowicz and David B. Rensch

J. Vac. Sci. Technol. B 5, 1707 (1987); http://dx.doi.org/10.1116/1.583652 (9 pages) | Cited 11 times

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The thermal stability of the physical, chemical, and electrical properties of W thin films sputter deposited on GaAs were investigated. A variety of characterization methods, including thin film stress analysis, Auger analysis, Rutherford backscattering spectrometry (RBS) analysis, and Schottky barrier measurements showed that the W/GaAs interface remains stable after high‐temperature furnace annealing at 900 °C for 15 min or rapid‐lamp annealing at 1000 °C for 11 s. Some refractory metal compounds were also investigated, including, WSi, WNx, and TaSix. Pure W films produced the best Schottky diode characteristics. The average Schottky barrier height was 0.70±0.009 V across a 2‐in wafer after furnace annealing at 800 °C/15 min. Pure W self‐aligned gate (SAG) metal‐semiconductor field‐effect transistors (MESFET) and digital circuits were also fabricated. Transconductances as high as 300 mS/mm (Lg =1.0 μm) were measured for enhancement mode SAG MESFET’s. Circuits were fabricated with SAG MESFET enhancement‐resistor mode logic using pure W gates, including ring oscillators, with gate delay as low as 25 ps and divide‐by‐eight circuits that functioned at a frequency >1 GHz.
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68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Refractory metal nitride rectifying contacts on GaAs

L. C. Zhang, C. L. Liang, S. K. Cheung, and N. W. Cheung

J. Vac. Sci. Technol. B 5, 1716 (1987); http://dx.doi.org/10.1116/1.583653 (7 pages) | Cited 8 times

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The electrical characteristics of reactive‐sputtered refractory metal nitride contacts on GaAs are investigated for their high‐temperature stability after rapid‐thermal annealed up to 850 °C for 10 s. It is observed that all the contacts studied, including ZrN/GaAs, TiN/GaAs, and NbN/GaAs systems, show improving rectifying characteristics with annealing temperatures up to 800–850 °C. Not only do they maintain excellent thermal stability and have ideality factors very close to unity, these refractory metal nitride/GaAs contacts actually exhibit a barrier height enhancement ranging from 0.13 eV for NbN/GaAs to 0.30 eV for ZrN/GaAs when contacts are annealed from 500 to 850 °C. Concomitantly, the small‐signal capacitance of the contacts decreases with higher annealing temperature. The breakdown characteristics of these contacts become avalanche‐like and the breakdown voltages increase by twofold. We have invoked the Shannon contact structure (i.e., metal/p+‐GaAs/n‐GaAs) to account for these high‐temperature induced properties. The p+‐GaAs layer formation is attributed to the incorporation of nitrogen into GaAs substrate during sputtering deposition. Comparison between pure refractory metals and their nitride contacts on GaAs are also made with electrical techniques (I–V, C–V) and material characterization techniques (Rutherford backscattering, scanning electron microscopy). Our study suggests that refractory metal nitrides have several advantageous properties for self‐aligned GaAs metal–semiconductor field‐effect transistor processes.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Nitrogen, oxygen, and argon incorporation during reactive sputter deposition of titanium nitride

D. S. Williams, F. A. Baiocchi, R. C. Beairsto, J. M. Brown, R. V. Knoell, and S. P. Murarka

J. Vac. Sci. Technol. B 5, 1723 (1987); http://dx.doi.org/10.1116/1.583654 (7 pages) | Cited 10 times

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For the reactive sputter deposition of titanium nitride, stress and resistivity of the films has been measured as a function of the processing variables target power, substrate bias, pressure, and N2/Ar ratio. These studies were limited to the conditions that produce titanium nitride of stoichiometry near 1. Through Rutherford backscattering spectroscopy, the changes in stress and the conductivity of the films as a function of the processing variables were interpreted in terms of nitrogen, argon, and oxygen concentration in the films. The increase in resistivity of the films correlates with increased oxygen incorporation and the increase in compressive stress of the films correlates with increased argon incorporation. The amount of oxygen in the films appears to produce a unique value of resistivity but the argon concentration that produces a given compressive stress is a function of the processing parameters that control argon incorporation.
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ng Insulators

Properties of TiSi2 as an encroachment barrier for the growth of selective tungsten on silicon

S. S. Chen, S. Sivaram, and R. K. Shukla

J. Vac. Sci. Technol. B 5, 1730 (1987); http://dx.doi.org/10.1116/1.583655 (6 pages) | Cited 2 times

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Selective growth of chemical‐vapor deposited selective tungsten, on thermally grown titanium silicide thin films, on silicon substrates, has been characterized. The nucleation of selective tungsten is found to be strongly affected by the surface chemical composition of the silicide. A thin layer of titanium nitride, formed on the silicide surface during the silicidation of sputtered titanium in nitrogen ambient, does not allow selective tungsten nucleation and has to be chemically removed to observe growth of the tungsten film. Localized titanium oxide regions on the silicide surface lead to adhesion problems between tungsten film and the silicide underlayer resulting in tungsten film blistering and bubbles formation. The regions of silicide where these bubbles form show accumulation of fluorine from the WF6 reduction at the interface. In regions of good adhesion and normal growth characteristics, no titanium oxide was found, almost all the silicide was consumed during the growth of selective tungsten and no fluorine accumulation at the interface was observed. These results indicate that it is possible to grow selective tungsten on titanium silicide barrier over silicon substrate provided that the surface of silicide is free of any titanium oxide or nitride layers. Under such conditions, the silicide layer acts as a sacrificial barrier allowing selective tungsten growth without resulting in any silicon consumption or encroachment of tungsten into the silicon substrate.
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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)
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains

Properties of direct current magnetron reactively sputtered TaN

Bhola Mehrotra and Jim Stimmell

J. Vac. Sci. Technol. B 5, 1736 (1987); http://dx.doi.org/10.1116/1.583826 (5 pages) | Cited 7 times

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Tantalum nitride has been investigated for use as a diffusion barrier between aluminum alloy interconnect and shallow source‐drain junctions in a 1‐μ‐complementary metal–oxide semiconductor technology. TaN films were reactively sputtered in a batch sputtering system equipped with dc magnetron cathodes, rf substrate bias, and independently controlled Ar and N2 sources. Film properties and their dependence on deposition parameters are discussed, and these properties are compared with those of titanium nitride films deposited using the same technique. Stoichiometric TaN films have resistivities of ∼220 μΩ cm. AlSi/TaN/Si contacts to shallow N+/P and P+/N junctions can withstand 575 °C 30 min heat treatments with no increase in junction leakage. The films can be etched in chlorine plasma chemistries typically used to etch aluminum alloys, and the aluminum etch has selectivity of ∼4:1 to TaN. This selectivity helps to protect inadvertently exposed Si junctions from damage during metal etch.
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68.35.Fx Diffusion; interface formation
73.61.Ng Insulators
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Characterization of titanium nitride films sputter deposited from a high‐purity titanium nitride target

T. Brat, N. Parikh, N. S. Tsai, A. K. Sinha, J. Poole, and C. Wickersham

J. Vac. Sci. Technol. B 5, 1741 (1987); http://dx.doi.org/10.1116/1.583630 (7 pages) | Cited 4 times

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Titanium nitride films (100–300 nm) were sputter deposited from a high‐purity titanium nitride target (nominal purity 99.99%) in an experimental dc‐magnetron system. The gold‐colored target, 5 cm in diameter, had a density of 92% of the theoretical value. X‐ray diffraction indicated that the target material matched the simulated stoichiometric TiN pattern, while the deposited films showed a shift in the crystallographic plane spacing of the (111) and (200) Bragg reflections. Rutherford backscattering spectrometry (RBS) performed on titanium nitride films which were deposited on amorphous carbon substrates indicated the presence of titanium, nitrogen, and oxygen as principal components of the films. No argon was detected in the films within the sensitivity of the RBS technique. Titanium to nitrogen atomic ratios in the films varied from 0.83 to 1.02 according to the RBS results. The binding energy measured by x‐ray photoelectron spectrometry (XPS) indicated that Ti and N were present in compound form. The effect of substrate temperature deposition, dc bias, and nitrogen content in the sputtering gas were correlated to the stoichiometry and resistivity of the films. High rates of deposition (3.8 nm/s) on hot Si(100) substrates produced films with a resistivity as low as 40 μΩ cm. The performance of the TiN films as a diffusion barrier was evaluated in a Al/TiN/TiSi2/Si(100) layered structure.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
68.35.Fx Diffusion; interface formation

Summary Abstract: Reactively sputtered RuO2 and Mo–O diffusion barriers

F. C. T. So, E. Kolawa, X.‐A. Zhao, E. T‐S. Pan, and M.‐A. Nicolet

J. Vac. Sci. Technol. B 5, 1748 (1987); http://dx.doi.org/10.1116/1.583631 (2 pages) | Cited 2 times

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Abstract Unavailable
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68.35.Fx Diffusion; interface formation
66.30.J- Diffusion of impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Properties of planar magnetron cosputtered silicide films

Jim Stimmell and Mike Strathman

J. Vac. Sci. Technol. B 5, 1750 (1987); http://dx.doi.org/10.1116/1.583632 (6 pages) | Cited 1 time

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Planar magnetron cosputtering (PMC) is a production technique for deposition of refractory metal silicide films. Films produced using this technique consist of alternating layers of metal and silicon, which intermix during subsequent thermal processing to form homogeneous, low‐resistivity films. The resulting films have low‐resistivities (28, 48, and 52 μΩ cm, respectively, for WSix, TaSix, and MoSx), and have very good oxidation and dry etch properties. This paper describes the PMC process and discusses the important deposition parameters. Two parameters, substrate bias level and substrate carrier rotation speed, produce effects not usually encountered for single‐component sputtered films. The influence of these two variables on film stoichiometry, as‐deposited resistivity, oxygen content, and density are examined. Changes in bias and rotation speed are found to produce repeatable changes in stoichiometry, as‐deposited resistivity, and density but do not appear to effect oxygen content. As‐deposited resistivity increases monotonically with silicon content and is a useful production process monitor. Evidence is also presented which suggests that properly prepared films exhibit very rapid interdiffusion during thermal annealing, and that considerable atomic mixing occurs during the deposition process. This conjecture is supported by the results of rapid optical anneals, which show that MoSix films can become homogeneous during 10‐s anneals at temperatures as low as 600 °C.
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81.15.Cd Deposition by sputtering
73.61.At Metal and metallic alloys
81.05.Bx Metals, semimetals, and alloys
68.55.Nq Composition and phase identification

The morphology and characteristics of TaSi2/Si films oxidized at high pressure

Yangyuan Wang, Jinhua Chen, Jiang Tao, Sunqi Feng, Ai‐Zhen Zhang, J. B. Stimmell, C. G. Hopkins, M. D. Strathman, and M. H. Herman

J. Vac. Sci. Technol. B 5, 1756 (1987); http://dx.doi.org/10.1116/1.583633 (4 pages)

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The oxidation of Ta silicide on Si substrates has been investigated for pressures from 1 to 10.7 atm. The oxidation of these films fits the Deal–Grove linear–parabolic model, with a direct proportionality of the rate constants to the oxidation pressure. In contrast to results reported for single‐crystal Si, the activation energies of the rate constants are found to depend upon pressure. Morphologically, transmission electron microscope micrographs show these oxidized silicide films to be rough, and possess SiO2 between grain boundaries. In addition, the dielectric strength of these oxides is found to be between 4 and 8 MV/cm.
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81.05.Bx Metals, semimetals, and alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.22.Jp Dielectric breakdown and space-charge effects
68.35.Dv Composition, segregation; defects and impurities
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