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Oct 1984

Volume 2, Issue 4, pp. 613-844


Effect of ion sputtering on interface chemistry and electrical properties of Au GaAs(100) Schottky contacts

Y.‐X. Wang and P. H. Holloway

J. Vac. Sci. Technol. B 2, 613 (1984); http://dx.doi.org/10.1116/1.582851 (7 pages) | Cited 20 times

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The effects of sputtering n–type (100)GaAs with 1 to 5 keV argon ions have been studied in ultrahigh vacuum. Auger electron and x‐ray photoelectron spectroscopies have been used to characterize the surface before and after sputtering. Gold Schottky contacts were prepared in situ to avoid contamination at the metal/semiconductor interface. The data show that sputtering depletes the surface in As, and the extent of depletion increased as the ion energy was increased. However, angular‐resolved photoelectron data showed As was enriched on the outer atom layer by 5 keV but depleted by 1 keV Ar+ sputtering. Current and capacitance versus voltage data showed that sputtering always lowered the Schottky barrier height and generally increased the ideality factor. However, the barrier height after 3 keV sputtering was higher than after 1 keV sputtering. Those effects are explained based on a combined effective work function model and creation of a donorlike surface damage layer. The donor layer was correlated with As depletion by sputtering. Deep level trap formation and annealing of sputtering effects were studied.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.40.Ns Metal-nonmetal contacts
61.80.Jh Ion radiation effects
68.60.-p Physical properties of thin films, nonelectronic

A nonalloyed, low specific resistance Ohmic contact to n‐InP

W. C. Dautremont‐Smith, P. A. Barnes, and J. W. Stayt

J. Vac. Sci. Technol. B 2, 620 (1984); http://dx.doi.org/10.1116/1.582847 (6 pages) | Cited 8 times

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Nonalloyed Ohmic contacts to n‐InP have been made by sputter deposition of metals onto sputter‐etched InP surfaces. Contacts were Ohmic as deposited without intentional heating. For a 500 Å sputter‐etch depth, the contact to 8×1018 cm−3 n‐InP was Ohmic up to 5×104 A cm−2 with a specific contact resistance of 4×10−7 Ω cm2 independent of sputter etch energy over the range 200 to 870 eV. To 6×1017 cm−3 n‐InP, the corresponding value was 1.8×10−6 Ω cm2. The In rich, degenerate n‐type sputter etch damaged surface is responsible for the quality of the contact, which is independent of the particular contacting metal, thus permitting the use of a barrier metal/noble metal combination. Nonalloyed contacts fabricated with Ti/Pt have low stress and excellent adhesion to InP. Even for the lowest etch energy, they are thermally stable, with no change caused by short periods up to 430 °C, or extended periods (∼100 h) at 250 °C. This contacting procedure and the resultant contact has many advantages over the usual Au:Sn or Au:Ge alloyed contact.
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73.40.Ns Metal-nonmetal contacts

Surface silicon oxynitride films obtained by implanting mixtures of oxygen and nitrogen ions into silicon

W. Streb and R. Hezel

J. Vac. Sci. Technol. B 2, 626 (1984); http://dx.doi.org/10.1116/1.582852 (4 pages) | Cited 4 times

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It was demonstrated that very thin silicon oxynitride films with concentrations covering the whole range between SiO2 and Si3N4 can be obtained by simultaneous high dose implantation of low energy oxygen and nitrogen ions into silicon. For ion energies of 5 keV homogeneous films about 5 nm in thickness resulted. These room‐temperature‐formed silicon oxynitride films were characterized by a combination of Auger electron spectroscopy (AES) and argon ion sputtering. The electron irradiation hardness was studied as a function of film composition.
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68.55.-a Thin film structure and morphology
61.72.U- Doping and impurity implantation
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
68.60.-p Physical properties of thin films, nonelectronic

Influence of slight deviations from TaSi2 stoichiometry on the high‐temperature stability of tantalum silicide/silicon contacts

H. Oppolzer, F. Neppl, K. Hieber, and V. Huber

J. Vac. Sci. Technol. B 2, 630 (1984); http://dx.doi.org/10.1116/1.582853 (6 pages) | Cited 2 times

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The influence of deviations from TaSi2 stoichiometry in cosputtered, amorphous Ta–Si films on interface reactions in contacts to silicon at 900 °C was investigated by TEM of thin cross sections through the contact windows. For Si rich films, the excess Si precipitates epitaxially in the contacts, whereas pits are formed for Ta rich films. Since the lateral Si transport involved ranges over several tens of microns, even a very small deviation from TaSi2 stoichiometry leads to strong degradation of the contacts. The interfacial oxide has no influence on the contact reactions. Since slight deviations from disilicide stoichiometry cannot be avoided with cosputtering, the realization of a low‐resistive, high‐temperature‐stable TaSi2 interconnection system with good contacts to Si would additionally require a high‐temperature‐resistant barrier layer. Experiments with a crystalline TaSi2 pad and a TaN0.8 barrier layer show insufficient stability at 900 °C, but suggest that most of the large lateral Si transport happens during the initial stage of crystallization.
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73.40.-c Electronic transport in interface structures

Low defect density insulating films deposited on room temperature substrates

J. H. Magerlein, John M. Baker, G. R. Proto, K. R. Grebe, S. P. Klepner, M. J. Palmer, and A. J. Warnecke

J. Vac. Sci. Technol. B 2, 636 (1984); http://dx.doi.org/10.1116/1.582854 (5 pages) | Cited 1 time

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Several types of thin dielectric films which can be deposited on substrates held near room temperature have been tested for use as insulators in integrated circuit structures. The types of insulation studied include single and double layer SiO films, Parylene polymer films, and SiO/Parylene composites. Test structures, which were fabricated with processes used in Josephson integrated circuits, allowed measurement of the number of electrical defects per unit area in the insulation between two Pb–In–Au films as well as the number of defects along edges of the lower metal film. The SiO/Parylene composite films had the lowest defect densities, as low as 0.2 cm−2 over planar metal layers and 0.001 cm−1 at insulated metal edges. Defect densities below those for single SiO films were also obtained by depositing the SiO in two layers through separate but indentical lift‐off stencils. The defect densities measured for these insulating films both before and after repeated thermal cycling to 4.2 K are believed to be adequate for proposed Josephson integrated circuits.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
77.55.-g Dielectric thin films
73.61.Ng Insulators

Maskless laser writing of silicon dioxide

R. R. Krchnavek, H. H. Gilgen, and R. M. Osgood

J. Vac. Sci. Technol. B 2, 641 (1984); http://dx.doi.org/10.1116/1.582855 (4 pages) | Cited 1 time

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A laser direct writing technique for forming insulating layers of silicon dioxide from an organosilicate film on various substrate materials is shown. The process resolution is a function of the thermal properties of the substrate and is shown to be 1 μm. The technique allows for a local variation in the oxide thickness by changing process parameters. The quality of the laser written layers is compared to similar films formed by conventional organosilicate processing.
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81.65.-b Surface treatments
79.20.Ds Laser-beam impact phenomena
85.40.Bh Computer-aided design of microcircuits; layout and modeling

An experimental system for surface reaction studies in microwave plasma etching

Ken Ninomiya, Keizo Suzuki, Shigeru Nishimatsu, Yoshitaka Gotoh, and Osami Okada

J. Vac. Sci. Technol. B 2, 645 (1984); http://dx.doi.org/10.1116/1.582856 (8 pages) | Cited 12 times

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An experimental system for studying surface reactions in the process of microwave plasma etching has been developed. In the system, a surface etched in the microwave plasma can be analyzed with x‐ray photoemission spectroscopy (XPS) without exposure of the surface to room air. In addition, we have developed a procedure for calculating a thickness of a surface layer stoichiometrically different from the substrate material and densities of atoms in the layer. Chemical changes in etched Si and SiO2 surfaces caused by exposing these surfaces to room air are investigated with XPS to show the utility of the system. When the surfaces etched in SF6 microwave plasma are exposed to room air, the chemical states of the surfaces change rapidly. This is mainly due to surface oxidation and adsorption of hydrocarbon compounds to the surfaces. The rapid changes are more clearly shown from increases in surface layer thickness and the number of O and C atoms in the layer. It is clarified that exposure of etched surface to room air causes the serious disturbance, and that accurate information can not be obtained any longer. The present system which eliminates this disturbance allows accurate measurement of surfaces for detailed investigation of the surface reaction in microwave plasma etching.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Reactive ion etching of GaAs using BCl3

G. J. Sonek and J. M. Ballantyne

J. Vac. Sci. Technol. B 2, 653 (1984); http://dx.doi.org/10.1116/1.582857 (5 pages) | Cited 12 times

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The reactive ion etching of GaAs has been investigated in BCl3 plasma discharges. Etching rates have been characterized as functions of pressure (10–25 mTorr), power density (∼0.05–0.5W/cm2), and Cl2/BCl3 gas compositions. Rates of ∼12–20 nm/min have been obtained, and are significantly lower than for other chlorinated plasmas. Etching profiles exhibit a high degree of anisotropy and smooth surface morphologies.
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81.65.-b Surface treatments
52.40.Hf Plasma-material interactions; boundary layer effects

Influences of molecular reflection on the lift‐off pattern edge quality

K. Arai, F. Yanagawa, and S. Kurosawa

J. Vac. Sci. Technol. B 2, 658 (1984); http://dx.doi.org/10.1116/1.582858 (7 pages)

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One of the problems in defining LSI patterns by the lift‐off technique is burrs, which appear at film pattern edges. The cause of burrs formed at the SiO film pattern edges is discussed. Burrs result from indirectly deposited thin layer residues on the resist pattern side walls. This layer is called a ‘‘side wall layer.’’ A model experiment is carried out and it is shown that the reflection of evaporated SiO molecules is the cause of indirect deposition. SiO molecule reflection probability during deposition is measured. The side wall layer is simulated using the reflection probability. It is concluded that reflection at the substrate surface and reflection at the vacuum chamber wall contribute to an equal degree to the side wall layer formation. Several methods of suppressing the side wall layer, which are also applicable to materials like Pb with higher reflection probability, are discussed. Cooling the substrate or the vacuum chamber, or setting up a shielding board in the chamber are predicted to be effective.
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81.65.-b Surface treatments
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Resolution of a three‐layer resist using heavy metal as an intermediate layer

Masanori Suzuki, Hideo Namatsu, and Akira Yoshikawa

J. Vac. Sci. Technol. B 2, 665 (1984); http://dx.doi.org/10.1116/1.582859 (5 pages)

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For the purpose of reducing radiation damage and delineating fine patterns in electron beam direct writing lithography, fundamental characteristics of a three‐layer resist using heavy metal as an intermediate layer is investigated in detail. An exposure and development simulation program, ELSIS, is extensively used to estimate resolution and linewidth control. The exposure intensity distributions for a line source are calculated to evaluate pattern delineation characteristics and degree of proximity effect in this three‐layer resist. The developed pattern profiles of positive‐type resist and absorbed energy density profiles in negative‐type resist are calculated. Some relevant experimental data also are presented. These results indicate that several advantages can be expected from this three‐layer resist, such as an apparent increase in resist sensitivity and a reduction of the interproximity effect.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena

Surface effects in γ‐ray‐induced changes of minority‐carrier lifetime

S. Hava

J. Vac. Sci. Technol. B 2, 670 (1984); http://dx.doi.org/10.1116/1.582860 (5 pages) | Cited 1 time

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Measurements of minority‐carrier lifetimes (τ) in shallow‐junction GaAs LED’s under varying gas‐pressure conditions prior to and following γ irradiation indicate (1) τ is noticeably influenced by gaseous ambient and, (2) this influence is greater following irradiation than prior to irradiation. This dependence of τ upon surface phenomena indicates γ irradiation changes surface conditions considerably. Combination of both mechanisms on surface effects can be utilized to bring about noticeable improvement in diode speed of response using only modest dosages of nuclear irradiation (up to 60% improvement for only 13 Mrad). It is believed that γ irradiation affects trap density particularly, while changes in gas type and pressure change both trap density and electron capture cross sections at the surface through adsorption–desorption processes. This is believed to be the first time γ ray induced decrease of τ has been studied in different post‐irradiation gaseous environments.
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61.80.Ed γ-ray effects
85.60.Jb Light-emitting devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photoemission studies of the interaction of hydrogen plasmas with GaAs(001)

P. Friedel, P. K. Larsen, S. Gourrier, J. P. Cabanie, and W. M. Gerits

J. Vac. Sci. Technol. B 2, 675 (1984); http://dx.doi.org/10.1116/1.582861 (6 pages) | Cited 7 times

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The interaction between hydrogen plasmas and a (001) surface of GaAs grown by molecular beam epitaxy is studied by photoemission using synchrotron radiation and reflection high energy electron diffraction (RHEED). Measurements of the As(3d) and Ga(3d) core levels show that the interaction is complex and bonding to both As and Ga occurs. It is seen from RHEED measurements that plasma exposures lead to an unreconstructed and partly disordered surface. Valence band studies by angle resolved photoemission show a prominent hydrogen induced feature in the heteropolar gap at an energy 7.7 eV below the valence band maximum.
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81.65.-b Surface treatments
52.40.Hf Plasma-material interactions; boundary layer effects

Large surface Fermi level shift in high temperature annealed metal–insulator–GaAs structures prepared in the presence of oxygen

R. Blanchet, C. Santinelli, J. Chave, M. Garrigues, S. Krawczyk, and P. Viktorovitch

J. Vac. Sci. Technol. B 2, 681 (1984); http://dx.doi.org/10.1116/1.582862 (3 pages)

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Experiments were conducted on two types of GaAs substrates according to the surface treatment which either resulted in oxidation of the substrate (chemical etching) or in nearly oxygen‐free interface (exposure of the substrate to a hydrogen/nitrogen mixture plasma). Owing to appropriate choices of the sequences of technological steps in the preparation of MIS samples, which include substrate treatment, deposition of the insulator (alumina obtained by reactive evaporation), and high temperature anneal (around 550 °C), it is given evidence of the great importance of the high temperature annealing step, solely responsible for the observed improvement in the electrical properties of the interface (as derived from capacitance and conductance measurements).
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Selective and anisotropic reactive ion etch of LPCVD silicon nitride with CHF3 based gases

T. C. Mele, J. Nulman, and J. P. Krusius

J. Vac. Sci. Technol. B 2, 684 (1984); http://dx.doi.org/10.1116/1.582863 (4 pages) | Cited 5 times

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The reactive ion etching (RIE) of silicon nitride (Si3N4) films formed by low pressure chemical vapor deposition (LPCVD), has been investigated. Studies were done using plasmas of CHF3, CHF3+O2, and CHF3+CO2 gases. Anisotropic profiles with vertical sidewalls and no undercut have been achieved with all three plasmas. The etch rate of the Si3N4 films in a pure CHF3 plasma was found to decrease as a function of time. This effect is explained via a mass transport limiting mechanism. Constant etch rates were observed with plasmas of CHF3+O2 and CHF3+CO2. A selectivity of 10:1 for the etching of Si3N4 to the underlying Si substrate has been achieved with a CHF3+CO2 plasma.
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81.65.-b Surface treatments

Interactions in metallization systems for integrated circuits

S. P. Murarka

J. Vac. Sci. Technol. B 2, 693 (1984); http://dx.doi.org/10.1116/1.582864 (14 pages) | Cited 10 times

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Conductive films are required to provide interconnection between contacts on the devices and between devices and outside world. Aluminum has been the most popular metal. Conducting polycrystalline silicon (polysilicon) film has been the conductor for gate and interconnection. PtSi has been used as a Schottky barrier contact and also simply as a contact for deep junctions. Refractory silicides are now used as gate and interconnection metallizations. Titanium/palladium/gold or titanium/platinum/gold beam lead technology was successful in providing high reliability connection to the outside world. Several similar schemes have been suggested or used in the integrated circuits. A considerable amount of work is carried out in adopting such a metallization scheme in integrated circuits. These include a study of metallurgical and chemical interactions between various materials and effect of such interactions on the properties of the materials and devices. In this paper a review of these studies will be presented.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Bh Computer-aided design of microcircuits; layout and modeling
84.32.Dd Connectors, relays, and switches

Effects of deposition parameters on the growth of thermal oxide on silicides over single crystal silicon

Wileen Chu, Aloke S. Bhandia, and James B. Stimmell

J. Vac. Sci. Technol. B 2, 707 (1984); http://dx.doi.org/10.1116/1.582865 (3 pages)

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A crucial criterion for utilizing silicide in MOS technologies is the ability to grow good thermal oxide. Silicides that are deposited or oxidized under nonoptimal conditions produce hazy or nonadherent oxides. The effects of three deposition parameters on subsequent oxide quality of planar magnetron cosputtered films were investigated. These variables are: (1) stoichiometry, (2) substrate bias, and (3) substrate rotation speed. The films were oxidized in steam at 920 °C for various time intervals. The appearances were determined visually. Oxide thicknesses were obtained. Substrate bias was observed to play a more critical role in oxide quality than the rotational speed. Changes in stoichiometry produced barely noticeable variations in oxide quality unless the films were too metal rich. Voids were not found to be an intrinsic characteristic of the oxide growth.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic
81.15.Cd Deposition by sputtering

Thermal‐wave measurements and monitoring of TaSix silicide film properties

W. Lee Smith, Jon Opsal, Allan Rosencwaig, James B. Stimmell, Jane C. Allison, and Aloke S. Bhandia

J. Vac. Sci. Technol. B 2, 710 (1984); http://dx.doi.org/10.1116/1.582866 (4 pages) | Cited 3 times

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There presently exists the need to measure the postanneal thickness of silicide films deposited on Si. In addition, there exists the need to monitor the deposition parameters of silicide films, since variations in the deposition process may alter the film stoichiometry, density, and preanneal electrical resistivity. In this paper we describe results of efforts to satisfy these needs using a thermal‐wave Therma‐Probe 100.
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68.60.-p Physical properties of thin films, nonelectronic
73.61.At Metal and metallic alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Impurities in refractory metals/silicides

S. C. Liang

J. Vac. Sci. Technol. B 2, 714 (1984); http://dx.doi.org/10.1116/1.582867 (4 pages) | Cited 1 time

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For the purpose of searching information on the desired purity specification optimum of refractory metal/silicide materials to be used by the IC manufacturer, the views of a material supplier are presented. In particular, ‘‘high purity’’ does not necessarily mean high quality, because all impurities are not equal. Samples of materials representing currently achievable production technology have been collected and analyzed (principally by spark‐source mass‐spectrometry). Impurities are grouped into three categories, the known sensitive elements (alkalis and α emitters particularly uranium/thorium), the major impurities (mostly the 4th period transition elements) which define the overall purity, and other impurities in lesser concentrations with ill‐defined effects on material usefulness. The uranium content as a source of soft error is discussed in some detail. A specification for refractory metals/silicides for VLSI application is proposed for industry consideration.
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61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Dopant redistribution in silicides: Materials and process issues

C. B. Cooper, R. A. Powell, and R. Chow

J. Vac. Sci. Technol. B 2, 718 (1984); http://dx.doi.org/10.1116/1.582868 (5 pages) | Cited 7 times

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The need to understand dopant redistribution in refractory metal silicides is important for reliable fabrication of polycide gates and other silicide‐containing structures in VLSI devices. This paper will review work on dopant redistribution in silicides with emphasis on polycide structures. Of particular concern is the high‐temperature sintering step required to form stable silicide and polycide structures. Results from conventional furnace sintering indicate that dopants can diffuse rapidly through certain silicides. The use of rapid thermal processing techniques to minimize dopant redistribution during the sintering step will also be reviewed. One conclusion is that our understanding of dopant redistribution in refractory metal silicides is limited and additional studies are required.
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61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
81.40.Gh Other heat and thermomechanical treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Radiation effects in TaSix/polysilicon MOS gate structures

Bruce L. Draper and Donald C. McKeon

J. Vac. Sci. Technol. B 2, 723 (1984); http://dx.doi.org/10.1116/1.582869 (7 pages) | Cited 3 times

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Silicide deposition methods, contamination of underlying oxide layers, and the use of high temperatures to crystallize the films are discussed in relation to their effects on radiation hardness. Large dose enhancement effects for photon energies ≲300 keV are predicted for MOS devices using TaSix/polysilicon gate electrodes. However, experiments at 15, 100, and 1000 keV show no large differences in threshold voltage shifts among MOS capacitors using Al/poly, TaSix/poly, and W/poly gates. Among devices using various gate materials, differences in the amount of interface state generation and hole trapping within the gate oxide after irradiation are attributed to differences in the amount of mechanical stress in the oxide layers.
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61.80.Ed γ-ray effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.-z Semiconductor devices
84.32.Tt Capacitors

Application of titanium polycide interconnects in a silicon‐gate process

Celia D. Gilfillan and Sal Spinella

J. Vac. Sci. Technol. B 2, 730 (1984); http://dx.doi.org/10.1116/1.582870 (3 pages)

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Devices which use titanium polycide to replace polysilicon in a silicon‐gate process have been processed and evaluated. The circuit used was designed for standard N‐channel Si‐gate processing, and was a standard production part. Working devices were obtained and life tested. Electrical characteristics of polycide wafers were compared with electrical characteristics of devices made from the same mask set using polysilicon interconnects. The titanium polycide wafers successfully completed life testing (1000 h of dynamic life testing at 125 °C) showing no degradation.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
73.61.-r Electrical properties of specific thin films

Plasma‐enhanced CVD of titanium silicide

Richard S. Rosler and George M. Engle

J. Vac. Sci. Technol. B 2, 733 (1984); http://dx.doi.org/10.1116/1.582871 (5 pages) | Cited 5 times

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The continuing trend toward smaller geometries and thinner junctions mandates that interconnect and gate materials have the lowest resistivity possible. Titanium silicide has the lowest resistivity of the refractory metal silicides and is, therefore, the prime candidate for advanced VLSI processing. This paper describes the CVD of titanium silicide in the ASM PECVD system. Reactor characteristics, deposition uniformities, and properties of the as‐deposited and annealed films are discussed. Film resistivity, after a 10 min anneal at 650 °C, is typically 15 to 20 μΩ cm. This result is obtained at a lower temperature (by about 100 °C) and lower resistivity (by about 25%) than is usually attainable with sputter‐deposited TiSix. Analysis using Rutherford backscattering spectrometry and Auger electron spectroscopy also indicates considerably better purity with these PECVD films. The step coverage of CVD TiSix is essentially conformal.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Impurity effects in transition metal silicides

C.‐D. Lien and M‐A. Nicolet

J. Vac. Sci. Technol. B 2, 738 (1984); http://dx.doi.org/10.1116/1.582872 (10 pages) | Cited 13 times

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Impurities can affect the properties of silicides directly by virtue of their presence. Impurities can also influence the processes by which silicides are formed. The effect of impurities on the reaction of transition metal films with a silicon substrate induced by thermal annealing are well documented. The interpretation of these results is discussed. It is shown that impurity redistribution is a major factor in determining how significant the effect of an impurity is. Redistribution observed for dopant impurities is also discussed.
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68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Applications of Rutherford backscattering spectrometry to refractory metal silicide characterization

Michael H. Herman

J. Vac. Sci. Technol. B 2, 748 (1984); http://dx.doi.org/10.1116/1.582873 (8 pages) | Cited 1 time

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Rutherford backscattering spectrometry (RBS) provides a unique combination of sensitivity and accuracy for characterization of thin films. Applications include analyses of composition, contamination levels, and determination of the thickness‐density product of both silicide layers and adjacent films. The large mass differences present in refractory metal silicide films make them ideally suited for RBS analysis. Excellent sensitivity, typically to tens of ppm for heavy elements, allows use of RBS for analyses of diffusion of refractory metals into other films, and study of cross‐contamination effects. This paper reviews the elements of Rutherford backscattering spectrometry which affect its applicability to refractory metal silicide analysis, and gives specific examples of these applications. The use of RBS analysis for determination of composition and contamination levels is demonstrated, including an estimation of the statistical uncertainty in such calculations. An example of trace refractory metal presence in an adjacent oxide layer is quantitatively calculated to be in the hundred ppm range. Further, the depth resolution generally accessible with normal angle detection is evaluated for various disilicides as a function of depth, and is found to be on the order of tens of nanometers. In addition, the development of two types of automated RBS data analysis is described. One type, a nonlinear least squares data analysis, provides accurate values for the average composition and density‐thickness product of multiple films. The value of such a program lies in its general applicability to any laterally uniform sample. The second method takes advantage of the separation of elemental signals, characteristic of thin film refractory metal silicide RBS spectra, to rapidly generate a composition depth profile.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.60.-p Physical properties of thin films, nonelectronic
07.75.+h Mass spectrometers
06.60.-c Laboratory procedures

Microstructural investigations of refractory metal silicide films on silicon

T. J. Magee, G. R. Woolhouse, H. A. Kawayoshi, I. C. Niemeyer, B. Rodrigues, R. D. Ormond, and A. S. Bhandia

J. Vac. Sci. Technol. B 2, 756 (1984); http://dx.doi.org/10.1116/1.582874 (6 pages) | Cited 5 times

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In a closely correlated study, we have investigated phase transformations and grain growth phenomena together with measurements of electrical resistivity in the silicides of tungsten, molybdenum, and tantalum. In the case of WSi2, we find the tetragonal structure at all temperatures of anneal between 700 and 1100 °C. Furthermore, the activation energy, 0.65 eV, derived from grain growth measurements is close to the value, 0.66 eV, derived from the increase in electrical conductivity. In the case of MoSi2, we find a mixture of hexagonal and tetragonal phases after annealing at 700 °C and pure tetragonal phase at 800 °C and above. Once again the activation energies derived from grain growth and electrical conductivity measurements are very similar. TaSi2 gives anomalous results compared with the other two silicides. Electrical conductivity shows an asymptotic behavior with increasing anneal temperature. This is probably related to the fact that tetragonal TaO2 was found in the films.
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68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Oxygen redistribution during sintering of Ti/Si structures

P. Merchant and Jun Amano

J. Vac. Sci. Technol. B 2, 762 (1984); http://dx.doi.org/10.1116/1.582875 (4 pages) | Cited 19 times

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We have used helium backscattering spectroscopy (RBS) to trace the evolution of oxygen depth profiles after UHV sintering, in 1430 Å titanium films, sputter deposited onto single crystal silicon substrates. The as‐deposited films exhibit a roughly exponential oxygen distribution, decreasing from the titanium film surface. After sintering at 350 °C, 30 min the oxygen has moved into the film and after 450 °C, 20 min the oxygen is uniformly distributed in the titanium. At higher temperatures, as silicide formation progresses, the oxygen is snowplowed back toward the surface and is completely driven from the TiSi2 film after sintering at 800 °C, 30 min. The low temperature oxygen redistribution in titanium correlates well with increases in the sheet resistance of the unreacted films, as has been suggested earlier from x‐ray diffraction results which revealed an increase in the titanium c axis after sintering at 500 °C [S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51, 342 (1980)]. The sheet resistance reaches a maximum near the onset of silicide formation and continues to decrease as the silicide reaction goes to completion. We do not detect any oxygen at the silicide/silicon interface, within the detection limits of RBS (1.5×1020 oxygen/cm3).
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81.40.Rs Electrical and magnetic properties related to treatment conditions
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.55.-a Thin film structure and morphology
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Stoichiometric shifts in cosputtered refractory silicide films during subsequent heat treatment

Aloke S. Bhandia

J. Vac. Sci. Technol. B 2, 766 (1984); http://dx.doi.org/10.1116/1.582876 (5 pages) | Cited 2 times

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Stoichiometric shifts in the refractory metal silicides due to subsequent thermal processing have been an important consideration in VLSI processing. Optimal stoichiometry for interconnect application has been controversial. Shift in silicon‐to‐metal atomic ratio of the metal silicide films, due to heat treatment under inert and oxidizing ambients, have been studied. Existence of a thermodynamical equilibrium stoichiometry has been investigated by studying films on both silicon and silicon dioxide. The silicide films were deposited by planar magnetron cosputtering and Rutherford backscattering was the primary technique used for monitoring the stoichiometry.
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68.60.-p Physical properties of thin films, nonelectronic
61.50.Nw Crystal stoichiometry
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Sputtering of refractory metal silicides from composite cathodes used in the Varian 3180/3190 sputtering system

Dennis R. Nichols

J. Vac. Sci. Technol. B 2, 771 (1984); http://dx.doi.org/10.1116/1.582877 (4 pages) | Cited 1 time

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The techniques and procedures utilized to sputter the silicides of Mo, Ta, and Ti in a Varian 3180/3190TM system1 are presented. The electrical resistivity of a thin film is a sensitive indicator of film purity and/or uniformity.2,3 The affect of various system parameters on film resistivity is also presented. Variable parameters investigated included argon pressure, cathode power, sputtering rate, wafer temperature, and wafer bias.
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81.15.Cd Deposition by sputtering
73.61.At Metal and metallic alloys

Influence of the interfacial oxide on titanium silicide formation by rapid thermal annealing

D. Pramanik, A. N. Saxena, Owen K. Wu, G. G. Peterson, and M. Tanielian

J. Vac. Sci. Technol. B 2, 775 (1984); http://dx.doi.org/10.1116/1.582878 (6 pages) | Cited 13 times

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The interaction of titanium films with single crystal silicon during rapid thermal annealing (RTA) has been studied by Auger analysis and SEM. The diffusion of silicon in titanium to form a silicide has been investigated as a function of the thickness of the interfacial silicon dioxide between the film and the substrate. For a clean interface the diffusion is initiated at lower temperatures, approximately 600 °C. Ion beam mixing of the interface caused by the implantation of heavy ions, such a arsenic, through the titanium film helps to render the interfacial oxide ineffective and thereby facilitates Si diffusion into the film. The presence of the interfacial oxide has been shown to affect the smoothness of the final silicide layer and the silicide–silicon interface. Silicide films produced from ion‐mixed films have been found to have smoother surfaces and interfaces than nonion‐mixed samples. Application of ion‐mixed films to devices has been studied.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
66.30.J- Diffusion of impurities

Phase equilibria in thin‐film metallizations

R. Beyers, R. Sinclair, and M. E. Thomas

J. Vac. Sci. Technol. B 2, 781 (1984); http://dx.doi.org/10.1116/1.582879 (4 pages) | Cited 47 times

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The determination of stable tie lines in a ternary phase diagram through a limited number of thin‐film reactions is demonstrated. Ternary phase diagrams are then used to explain the stability of refractory metals, silicides, and nitrides during various integrated circuit processing steps. The W–Si–O, Ti–Si–O, Ti–Si–N, and Ti–Al–N systems serve as examples.
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64.70.K- Solid-solid transitions
68.60.-p Physical properties of thin films, nonelectronic

Overview of coating technologies for large scale metallurgical, optical, and electronic applications

R. F. Bunshah

J. Vac. Sci. Technol. B 2, 789 (1984); http://dx.doi.org/10.1116/1.582880 (11 pages) | Cited 2 times

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There are hardly any high technology applications which do not involve composite materials with a coating of specific properties on a substrate with another set of properties. This overview is concerned with the various coating methods for a variety of substrates for metallurgical, optical, and electronic applications. Selection criteria for process/apparatus for large scale applications are presented. Economic considerations are discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

New coatings for high temperature materials protection

M. J. Bennett

J. Vac. Sci. Technol. B 2, 800 (1984); http://dx.doi.org/10.1116/1.582881 (6 pages) | Cited 6 times

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The development, characterization, and performance evaluation of two new thin (≲20 μm) ceramic coatings for high temperature materials protection is reviewed. These coatings were silica produced by two vapor deposition procedures and ceria formed by sol–gel technology. The current position regarding the use of these coatings in the UK nuclear industry is described.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Bx Metals, semimetals, and alloys

Diffusion coatings of steels: Formation mechanism and microstructure of aluminized heat‐resistant stainless steels

N. V. Bangaru and R. C. Krutenat

J. Vac. Sci. Technol. B 2, 806 (1984); http://dx.doi.org/10.1116/1.582882 (10 pages) | Cited 6 times

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The effect of base‐alloy composition on the microstructure and mechanical and thermal stabilities of aluminum diffusion coatings has been studied for 316, 310, and I800H stainless steels, by optical, microprobe, transmission/scanning transmission electron microscopy, and microhardness testing. In all the diffusion aluminized alloys, two distinct coating layers form: an outer aluminide layer and an inner, interdiffusion layer. The substrate austenite stability is the single most important parameter affecting the thickness, phase distribution, and microchemistry of these two layers. TEM/STEM analyses showed that the interdiffusion layer is a ‘‘natural composite’’ made up of a uniform dispersion of the hard nickel aluminide phase (B2) in a soft ferrite matrix. Formation of this layer involves ‘‘ferritization’’ of the substrate, a process akin to pearlitic transformation in carbon steels. The interdiffusion layer demonstrated high hardness with good mechanical integrity and its thermal stability with the substrate depends strongly on the ease of ferritization, which depends in turn on the degree of austenite stability of the substrate.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
68.55.-a Thin film structure and morphology
66.30.J- Diffusion of impurities

Thin solid films to combat friction, wear, and corrosion

H. E. Hintermann

J. Vac. Sci. Technol. B 2, 816 (1984); http://dx.doi.org/10.1116/1.582883 (7 pages) | Cited 2 times

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This paper deals with the relations and interactions of the substrate, the interface, and the functional hard overlay or diffusion coating deposited by chemical or physical vapor deposition, CVD or PVD, respectively, and how these structures influence the overall mechanical and physicochemical properties of the composite. Emphasis is given to the friction and wear behavior of the refractory carbides, nitrides, borides, and oxides, with and without lubrication, to the characterization of the mechanical strength of the interface as measured by the scratch test and thus, of the adhesion and cohesion properties, and to the corrosion behavior, mainly of TiC.
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81.05.Bx Metals, semimetals, and alloys
68.60.-p Physical properties of thin films, nonelectronic

Xerographic photoreceptors

J. Mort

J. Vac. Sci. Technol. B 2, 823 (1984); http://dx.doi.org/10.1116/1.582884 (4 pages) | Cited 1 time

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A brief survey is given of the use of amorphous materials as xerographic photoreceptors. Included are a discussion of the basic physics and materials parameters required for operational devices and the methods of fabrication. The review includes current material classes such as chalcogenides and organic solids and new potential photoreceptors based on hydrogenated amorphous silicon.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
72.40.+w Photoconduction and photovoltaic effects
78.90.+t Other topics in optical properties, condensed matter spectroscopy and other interactions of particles and radiation with condensed matter (restricted to new topics in section 78)
89.70.-a Information and communication theory

Thin film transistors for large area electronics

Malcolm J. Thompson

J. Vac. Sci. Technol. B 2, 827 (1984); http://dx.doi.org/10.1116/1.582902 (8 pages) | Cited 4 times

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This paper reviews thin film transistor technology with a detailed emphasis on amorphous silicon (a‐Si:H) devices. The fabrication and large area technology issues are described. The materials parameters that affect device performance are dominated by interface effects and the gate dielectric. The problem of characterizing the interfaces is discussed. Applications in liquid crystal displays (LCD) and image sensors are described. It is concluded that there is considerable promise for this rapidly expanding technology.
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85.30.-z Semiconductor devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.60.Jb Light-emitting devices
68.55.-a Thin film structure and morphology

Amorphous silicon solar cells

S. R. Ovshinsky

J. Vac. Sci. Technol. B 2, 835 (1984); http://dx.doi.org/10.1116/1.582903 (5 pages) | Cited 7 times

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The direct conversion of sunlight into electricity has been a utopian dream. The ability to generate electricity in this manner is, of course, exciting since it utilizes nondepletable fuel and is nonpolluting. However, since the 1950’s, the approach to accomplish this aim has been primarily through the utilization of expensive crystalline silicon solar cells. We describe here how noncrystalline materials, that is, amorphous materials, can be produced as continuous, large‐area, thin‐film devices with efficiencies, stabilities, and costs which will permit them, for the first time, to compete realistically with conventional fuels such as oil, gas, uranium, and coal.
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84.60.Jt Photoelectric conversion

Economics of processing thin‐film solar cells

T. W. F. Russell, B. N. Baron, and R. E. Rocheleau

J. Vac. Sci. Technol. B 2, 840 (1984); http://dx.doi.org/10.1116/1.582904 (5 pages)

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The commercial‐scale processing potential for photovoltaic devices based on polycrystalline and amorphous silicon thin films is evaluated by analyzing in detail the semiconductor deposition process for the following material layers: (CdZn)S/CuInSe2, CdS/CdTe, (CdZn)S/Cu2S, and amorphous silicon. The current status of both laboratory‐scale and unit‐operations‐scale experiments is tabulated and the goals required for reasonable commercial‐scale production detailed. The costs of manufacture are estimated and it is shown that all thin‐film materials which have achieved 10% efficiency in the laboratory can be manufactured at a cost well below one dollar per watt, provided the manufacturing facilities can be designed to produce between 100 000 and 1 000 000 square meters per year. The critical thin‐film research areas are identified for each of the materials listed above.
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84.60.Jt Photoelectric conversion
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