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Nov 1992

Volume 10, Issue 6, pp. 3395-3589


Optical emission investigation of the plasma enhanced chemical vapor deposition of silicon oxide films

A. Banerjee and T. DebRoy

J. Vac. Sci. Technol. A 10, 3395 (1992); http://dx.doi.org/10.1116/1.577790 (6 pages) | Cited 4 times

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During plasma enhanced chemical vapor deposition of silicon oxide films, plasma diagnostics is important for process control and reproducibility of film quality. In this study the film growth rate has been investigated with special emphasis on plasma properties to seek a better understanding of the deposition process. Light emissions from the plasma were monitored using an optical multichannel analyzer for various deposition conditions. The electron temperature and density were determined from the spectral data. With increasing silane concentration, the number density of the electrons, the concentrations of active species and the deposition rate increased. The growth rate also increased with nitrous oxide concentration. However, the emission intensities did not show a concomitant increase because of the radiation quenching effect. Analysis of the results emphasizes the crucial importance of electron density to generate sufficient concentration of active species responsible for determining the film growth rate. Among the peaks monitored, the intensity of a hydrogen peak correlated well with the deposition rate. The hydrogen peak intensity can be used for reliable, on‐line, non‐contact, instantaneous monitoring of the film growth rate.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High‐rate aluminum oxide deposition by MetaModeTM reactive sputtering

J. P. Lehan, R. B. Sargent, and R. E. Klinger

J. Vac. Sci. Technol. A 10, 3401 (1992); http://dx.doi.org/10.1116/1.577791 (6 pages) | Cited 4 times

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MetaModeTM reactive sputtering was employed to produce optical quality aluminum oxide films at rates an order of magnitude higher than those possible with conventional reactive magnetron sputtering. System pressure, reactive‐to‐nonreactive gas flow ratio, and ion‐source current density were varied to investigate their effects on rate, process stability, and film properties. It was found that the coatings deposited at a reduced pressure (0.27 Pa) produced dense, water‐free coatings without compromising optical quality or deposition rate.
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81.15.Cd Deposition by sputtering
81.40.Tv Optical and dielectric properties related to treatment conditions

Radiative substrate heating for high‐Tc superconducting thin‐film deposition: Film‐growth‐induced temperature variation

A. C. Westerheim, B. I. Choi, M. I. Flik, M. J. Cima, R. L. Slattery, and Alfredo C. Anderson

J. Vac. Sci. Technol. A 10, 3407 (1992); http://dx.doi.org/10.1116/1.577792 (4 pages) | Cited 6 times

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We have examined the problem of substrate temperature changes during the growth of YBa2Cu3O7−x (YBCO) thin films on LaAlO3 when the substrate is radiatively heated. Substrate temperature variations sufficient to degrade film quality occur unless the heater temperature is controlled during growth. At a heater temperature of 900 °C, the temperature of a LaAlO3 substrate was measured to be only 540 °C, while a similar substrate with a 2000‐Å YBCO film reached 640 °C. The experimental data and calculations indicate that the heater temperature must be as high as 1240 °C to heat LaAlO3 to 730 °C, and must be decreased by over 200 °C during the first 500 Å of film deposition to maintain a constant substrate temperature during film growth. This study shows the need for an in situ noncontact substrate temperature measurement technique.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
68.55.-a Thin film structure and morphology

Fabrication of superconducting YBa2Cu3O7−δ submicron structures

R. Barth, B. Spangenberg, W. Langheinrich, W. Albrecht, H. Kurz, G. Gieres, and B. Holzapfel

J. Vac. Sci. Technol. A 10, 3411 (1992); http://dx.doi.org/10.1116/1.577793 (3 pages) | Cited 5 times

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Submicron structures of superconducting YBa2Cu3O7−δ (δ<0.1) are fabricated by high‐energy electron‐beam lithography in combination with Ar/O2 ion‐beam etching. A novel three‐level resist system of platinum/titanium/PMMA is developed to minimize the process‐induced loss of superconductivity. Bridges as narrow as 150 nm with lengths between 0.3 and 4 μm have been fabricated, retaining their superconductivity without reloading with oxygen. Possible reasons for process‐induced deterioration of superconducting properties are discussed.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
85.40.Hp Lithography, masks and pattern transfer

Energetic carbon deposition at oblique angles

Jerome J. Cuomo, David L. Pappas, Richard Lossy, James P. Doyle, John Bruley, Gregory W. Di Bello, and William Krakow

J. Vac. Sci. Technol. A 10, 3414 (1992); http://dx.doi.org/10.1116/1.577794 (5 pages) | Cited 6 times

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Carbon is energetically deposited by pulsed laser vaporization, cathodic arc and ion beam sputtering to provide amorphous diamond films with varying degrees of diamondlike quality. Laser and arc films prepared at normal particle incidence are high in sp3 content and electrical resistivity, and exhibit optical behavior comparable to diamond. As the incident angle of the depositing species becomes increasingly oblique, the diamondlike character is progressively degraded. This is verified by decreases in sp3 fraction, resistivity, and optical transmittance. These changes are accompanied by a roughening of the microstructure, but no apparent variation in the transmission electron diffraction pattern. For deposition at the most oblique angles, the development of biaxial stress anisotropy is observed, as the compressive stress measured along the direction of incidence decreases at a greater rate than along the perpendicular direction. The implications of these results on the mechanisms proposed for amorphous diamond formation are discussed.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Electron cyclotron resonance plasma experiment for in situ surface modification, deposition, and analysis

S. Nowak, P. Gröning, O. M. Küttel, M. Collaud, and G. Dietler

J. Vac. Sci. Technol. A 10, 3419 (1992); http://dx.doi.org/10.1116/1.577795 (7 pages) | Cited 10 times

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An electron cyclotron resonance plasma source which allows in situ surface modification and thin film deposition combined with surface analysis by x‐ray photoelectron spectroscopy (XPS) is presented. This experiment enables well defined surface modification studies to be performed. We discuss the experimental details of this plasma source as well as the main discharge characteristics as a function of gas, pressure, and geometry. Using plasma diagnostics, a Langmuir probe and an ion energy analyzer, the ion density, the electron temperature, and the ion flux were determined. Two examples of applications analyzed by XPS, one for surface modification and one for thin film deposition, confirm the ability to produce well defined and contamination‐free surfaces.
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52.75.-d Plasma devices
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Resonant inductive plasma etching evaluation of an industrial prototype

D. Henry, J. M. Francou, and A. Inard

J. Vac. Sci. Technol. A 10, 3426 (1992); http://dx.doi.org/10.1116/1.577796 (4 pages) | Cited 1 time

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The development of the resonant inductive plasma etcher was undertaken in order to satisfy the ultra large scale integrated manufacturing requirements. We present in this article an evaluation of this equipment, based upon test processes as support for pointing out the specific advantages and limitations of the reactor. Plasma chemistries such as SF6 and HBr have been studied. Silicon trench etching and polysilicon gate etching results are reported. Studies have been made at both low‐pressure range (1 μbar), and at higher pressure range (7 μbar), even though the equipment was not optimized for this operating pressure range. We present successful results for polysilicon gate etching at low pressure; whereas for trench etching, we show that a higher pressure is more suited to satisfying the requirements of such a process.
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81.65.-b Surface treatments
52.75.-d Plasma devices

High‐vacuum planar magnetron discharge

T. Asamaki, T. Miura, G. Nakamura, K. Hotate, S. Yonaiyama, K. Ishibashi, and N. Hosokawa

J. Vac. Sci. Technol. A 10, 3430 (1992); http://dx.doi.org/10.1116/1.577797 (4 pages)

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The present article demonstrates the possibility of developing a high‐vacuum planar magnetron discharge. Until recently, developed cathodes applying a high electric field and a high magnetic field which cross each other in a discharge space enable the discharge to be sustained at 0.1 Pa. Experimental results of this article show that even at pressures lower than 10−3 Pa the discharge can be sustained. The discharge intensity I/P is proportional to the discharge voltage and depends strongly on the magnetic flux density. It is found that the high‐vacuum planar magnetron discharge requires a magnetic flux density higher than 0.1 T and a discharge voltage higher than 2 kV, for its effective sustenance. Sputtering of aluminum by this discharge is performed and the deposition rate 0.2 μm/min is obtained.
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52.80.Pi High-frequency and RF discharges
52.75.-d Plasma devices
81.15.Cd Deposition by sputtering

Effects of hydrogen, nitrogen, and oxygen on the crystallographic and magnetic properties of sputtered (Co–Ni–Zr)/Cr thin film recording media

Hiroyuki Suzuki, Yoshihiro Shiroishi, Yoshibumi Matsuda, and Tomoyuki Ohno

J. Vac. Sci. Technol. A 10, 3434 (1992); http://dx.doi.org/10.1116/1.577798 (5 pages) | Cited 1 time

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The effects of additive gases of hydrogen, nitrogen, and oxygen on the crystallographic and magnetic properties of sputtered (Co–Ni–Zr)/Cr thin film recording media have been studied. The results show that oxygen and nitrogen affect the coercive force more severely than hydrogen does. However, no significant changes in saturation magnetization are observed due to the introduction of additive gases during deposition. The in‐plane epitaxial growth of a Co–Ni–Zr alloy magnetic layer on a Cr underlayer is degraded due to surface oxidation of the Cr underlayer by oxygen introduction and is also degraded due to lattice expansion of the Cr underlayer by nitrogen introduction.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Compositional dependence of stress in silver copper alloys prepared by direct current magnetron sputtering

A. M. Kazakos, D. E. Fahnline, R. Messier, and L. J. Pilione

J. Vac. Sci. Technol. A 10, 3439 (1992); http://dx.doi.org/10.1116/1.577799 (6 pages)

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Metal thin films were prepared by dc magnetron sputtering in an argon plasma at a pressure of 2.5 mTorr and ambient temperatures. Alloy films of Ag–Cu were deposited by simultaneous sputtering of the two elemental targets, as well as metal films of Ag and Cu by sputtering from the appropriate pure target. Cosputtering provides a simple, direct method of preparing alloy films across the entire compositional range, as an alternative to sputtering from diphasic targets of single compositions. The low sputtering pressure utilized in this study insured the preparation of dense, smooth, highly reflective films, indicative of energetic ion bombardment. Total film stress was evaluated as a function of atomic composition and thickness (500, 1000, and 1500 Å). Extensive x‐ray diffraction (XRD) analysis was performed to identify the alloy phases present, calculate their lattice constants, and determine orientation. The film stress became more compressive with increasing film thickness for each of the films studied. In addition, the film stress was found to vary as a function of film composition. The oscillation of the stress curve between tension and compression is explained by the atomic peening, increased grain boundary, phase separation, and plastic flow models.
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties

Compositional dependence of grain size in silver copper alloys prepared by direct current magnetron sputtering

A. M. Kazakos, D. E. Fahnline, R. Messier, and L. J. Pilione

J. Vac. Sci. Technol. A 10, 3445 (1992); http://dx.doi.org/10.1116/1.577800 (6 pages)

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Cosputtering provides a simple, direct method of preparing alloy films across the entire compositional range, as an alternative to sputtering from diphasic targets of single compositions. Metal thin films were prepared by dc magnetron sputtering in an argon plasma at a pressure of 2.5 mTorr and ambient temperatures. Alloy films of Ag–Cu were deposited by simultaneous sputtering of the two elemental targets, as well as metal films of Ag and Cu by sputtering from the appropriate pure target. The low sputtering pressure utilized in this study insured the preparation of dense, smooth, highly reflective films, indicative of energetic ion bombardment. X‐ray diffraction (XRD) was performed to identify the alloy phases present and estimate their crystallite size. Transmission electron microscopy (TEM) was utilized to observe the microstructure and estimate grain size. Electrical resistivity measurements were carried out at room temperature on 1500 Å thick, pure and alloy metal films to complement XRD and TEM results. A dramatic reduction in grain size from that of pure metal was detected when the second element was simultaneously sputtered. Electrical resistivity of the alloys increased from that of the pure films. A region of greatest resistivity was noted and found to correspond to the smallest grain size, which occurred between 40 and 70 at. % Cu.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
73.61.At Metal and metallic alloys

Optical properties of ion assisted deposited zirconia thin films

M. Ghanashyam Krishna, K. Narasimha Rao, and S. Mohan

J. Vac. Sci. Technol. A 10, 3451 (1992); http://dx.doi.org/10.1116/1.577801 (5 pages) | Cited 2 times

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The nature of the dependence of refractive index, extinction coefficient, and packing density of zirconia films prepared by ion assisted deposition on the energy and current density of ions has been investigated. A broad beam Kaufman ion source has been used to generate oxygen ions in the energy range 100–700 eV and current densities up to 220 μA/cm2. It has been found that the refractive index increases steadily up to an energy of 500 eV beyond which there is a nominal decrease. The highest index obtained was 2.21 at an energy of 500 eV and a current density of 220 μA/cm2. Similarly, with an increase in the current density the refractive index increases initially and seems to saturate beyond a certain critical value dependent on the ion energy. The extinction coefficient was low up to an energy of 300 eV showing a marked increase thereafter. The extinction coefficient was also found to increase at high ion current densities and energies. A critical ion energy and current density beyond which the refractive index as well as the extinction coefficient of these films start deteriorating has been observed.
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78.66.-w Optical properties of specific thin films
81.15.Cd Deposition by sputtering
81.40.Tv Optical and dielectric properties related to treatment conditions

Formation of high adhesive and pure Pt layers on TiO2

Ichiharu Kondo, Takao Yoneyama, Osamu Takenaka, and Akira Kinbara

J. Vac. Sci. Technol. A 10, 3456 (1992); http://dx.doi.org/10.1116/1.577802 (4 pages) | Cited 16 times

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The formation of a high adhesive noble metal layer on an oxide layer has been investigated in the Pt/(Ti)/TiO2/SiO2/Si system, prepared in a vacuum evaporation apparatus. The thermosonic ball bonding test and the conventional pull test were successively applied to the evaluation of adhesion. The Ti inserted layer between the Pt and the TiO2 layer was found to improve the adhesion. A Ti layer of approximately 10 nm was found to be necessary for stronger adhesion. Auger electron spectroscopy (AES) depth profile results showed that a part of the Ti atoms in the inserted layer were segregated to the Pt surface from the interface by annealing at 1373 K for 30 min, while the rest of Ti atoms in the inserted layer remained and acted as a ‘‘glue’’ at the interface between the Pt and the TiO2 layer. It should be noted that Ti could not be detected in the Pt layer within the AES detection limits. Scanning electron microscope and energy dispersive x‐ray spectroscopy observations showed that Ti diffusion occurred through the grain boundaries of the Pt layer and Ti atoms appeared at surface grain boundaries on top of the Pt layer.
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68.60.Wm Other nonelectronic physical properties
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
66.30.J- Diffusion of impurities

Titanium and tantalum coatings on aluminum nitride

W. B. Carter and M. V. Papageorge

J. Vac. Sci. Technol. A 10, 3460 (1992); http://dx.doi.org/10.1116/1.577803 (5 pages) | Cited 4 times

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Thin films of titanium and tantalum were deposited on aluminum nitride substrates by vacuum evaporation at T=573 K. Pull tests of film/substrate interfacial strengths yielded 57.57±14.41 and 67.71±9.31 MPa for Ti/AlN and Ta/AlN, respectively. The coatings have been examined by profilometry, scanning electron microscopy, x‐ray diffraction, Auger electron spectroscopy (AES) and x‐ray photoelectron spectroscopy (XPS). Depth profiles were performed with both AES and XPS. The data indicate that nitrogen, from either the substrates or their surfaces, diffuses into the titanium films and combines with them chemically. No clear evidence for a similar reaction between tantalum films and the AlN substrates was found.
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68.35.Fx Diffusion; interface formation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
66.30.Ny Chemical interdiffusion; diffusion barriers

Influence of recrystallization on the outgassing characteristics of copper

Akihito Kurosaka, Osamu Nakao, Toshiaki Yoshikawa, and Masao Ueki

J. Vac. Sci. Technol. A 10, 3465 (1992); http://dx.doi.org/10.1116/1.577804 (7 pages)

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Disk specimens were prepared from high‐purity copper and oxygen‐free copper, which had a residual resistance ratio (RRR; p298 K/p4.2K) of 5450 and 207, respectively, and thermal desorption spectroscopy (TDS) measurement was applied for evaluating outgassing characteristics of those. For these types of pure copper, outgassing was encouraged by primary and secondary recrystallization. Particularly, the TDS spectra of H2, CO, CH4 and CO2, obtained from an as‐rolled specimen of the high‐purity copper, exhibited sharp peaks at the primary recrystallization stage. The outgassing characteristics of these pure copper depended on their recrystallized textures, so the amount of outgassing became lower with growing of recrystallized grains. With the high‐purity copper, whose recrystallized grains were grown even by low‐temperature annealing, secondary recrystallization progressed more rapidly than that with the oxygen‐free copper.  
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07.30.Bx Degasification, residual gas

Photoemission of adsorbed xenon study of surface defects generated by ion bombardment of Ni(111)

Geoffrey P. Malafsky, Sabrina S. Fu, and David S. Y. Hsu

J. Vac. Sci. Technol. A 10, 3472 (1992); http://dx.doi.org/10.1116/1.577805 (6 pages)

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The surface defect density generated by 1.0 keV Ar+ ion bombardment of a Ni(111) crystal at 88 K is studied with photoemission of adsorbed xenon (PAX). The defect sites are distinguished by the position of the Xe 3d5/2 peak. The peak position reflects the local electrostatic potential at the Xe adsorption site that is modified at a defect site from the terrace sites by the electron‐density smoothing process. The PAX spectra of the ion bombarded surfaces have peaks at 669.3 eV from Xe adsorbed at terrace sites, 670.0 eV from Xe at step sites, and 671.0 eV. We ascribe the latter peak to Xe adsorbed at small vacancy islands or kink sites where the Xe atom can experience a larger electrostatic potential perturbation compared to Xe adsorbed at a step site producing the additional 1 eV shift to higher binding energy. The PAX spectra are acquired with two ambient Xe pressures, 7×10−10 and 5×10−6 Torr. At low Xe pressure, the total Xe coverage and step peak intensity rapidly increase with low ion fluence with initial rates of 3 Xe atoms/ion for the total Xe coverage and 1.5 Xe atoms/ion for the step sites in the first 2.9×1013 ions/cm2 fluence. In contrast, at high Xe pressure, the total Xe coverage, and the terrace peak intensity decrease rapidly in the same region of ion fluence with initial rates of −3 Xe atoms/ion for the total Xe coverage and −5 Xe atoms/ion for the terrace peak. The rate of decrease of the terrace peak intensity corresponds to 15 Ni terrace atoms uncovered per incident ion since the large Xe atom covers three terrace atoms. The loss of Xe coverage on terrace sites likely results from the destruction of the long‐range order in the Xe two‐dimensional solid on the ion bombardment roughened surface.
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61.80.Jh Ion radiation effects
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Study of fluorine (XeF2) adsorption and of oxygen/fluorine coadsorption on silicon using infrared reflection absorption spectroscopy

V. M. Bermudez

J. Vac. Sci. Technol. A 10, 3478 (1992); http://dx.doi.org/10.1116/1.577806 (8 pages) | Cited 14 times

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Infrared reflection absorption spectroscopy has been used to study the chemisorption of fluorine (by exposure to XeF2) on polycrystalline Si surfaces in ultrahigh vacuum and under low‐pressure steady‐state conditions. Adsorption at 300 K leads to the sequential formation of mono‐, di‐, and trifluoride SiFx groups. Annealing at successively higher temperature forms more ≡SiF by decomposition of =SiF2 and –SiF3. After a 770 K anneal, only the 890 cm−1 ≡SiF band remains and is removed by F desorption at ∼820 K. Similar results are obtained in a continuous XeF2 flux with, in addition, the appearance near 300 K of a weak feature possibly due to adsorbed SiF4. Based in part on these results, an estimate can be made of the rate‐limiting step in the reaction. In the high‐temperature limit (T≥650 K) it appears to be the conversion of ≡SiF to =SiF2; whereas, near 300 K, it is the formation of SiF4 from –SiF3. The effects on fluorination of pre‐ and postexposure to O2 have also been observed. Preadsorbed O stabilizes F, shifting the F desorption temperature higher by at least 100 K. In the presence of coadsorbed F, the Si–O–Si antisymmetric stretch appears at 1150 cm−1, significantly higher than on a similar, F‐free surface. Preadsorbed F impedes subsequent chemisorption of O2, and the O that is adsorbed has no apparent effect on SiFx bonding as reflected in the Si–F stretching vibrations.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Commensurate–incommensurate phase transition between 6×6 and √3×√3 + satellite structures of the Au/Si(111) surface

J. Yuhara, M. Inoue, and K. Morita

J. Vac. Sci. Technol. A 10, 3486 (1992); http://dx.doi.org/10.1116/1.577807 (7 pages)

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Alternate annealing in the low‐ (≤250 °C) and high‐ (≥400 °C) temperature regimes of the Au/Si(111) surface at different Au coverages prepared by room‐temperature deposition and isothermal annealing in the high‐temperature regime at over‐(ML) coverages have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectroscopy (RBS). It is found that the 6×6 pattern and the √3×√3+satellite pattern are formed at 0.9–2.2 ML coverages by annealing for several minutes at 250 and 500 °C, respectively, when there exist an Au surface peak and a diffusion tail extended towards the lower energy behind the Au peak and that the phase transition between both patterns is reversible by alternate annealing in two temperature regimes as long as the diffusion tail is not diminished. From this result, the 6×6 structure is ascribed to excess embedded Au atoms situated at the ordered sites and Au atoms constituting the √3×√3 structure at the top surface. Moreover, it is found that the phase transition between the √3×√3 structure and the mixed structure of √3×√3+5×1 are also reversible by alternate annealing in the two temperature regimes at the actual coverages of 0.72–0.84 ML. Furthermore, from analysis of the isochronal annealing data at 1.7 ML, the activation energy of the diffusion of Au in Si is found to be 1.3 eV.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
64.70.Rh Commensurate-incommensurate transitions

Gas–plasma interactions in a filtered cathodic arc

M. K. Puchert, C. A. Davis, D. R. McKenzie, and B. W. James

J. Vac. Sci. Technol. A 10, 3493 (1992); http://dx.doi.org/10.1116/1.577808 (6 pages) | Cited 2 times

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The physical interactions between the metal plasma beam of a filtered cathodic arc and noble gases introduced into the beam path are studied. Langmuir probe measurements show that the ion saturation current increases rapidly and nonlinearly with pressure until a cutoff point, after which there is a general decrease with a reproducible fine structure in the form of subsidiary maxima and minima. For helium, the electron density increases exponentially by two orders of magnitude, as the pressure rises from base pressure. Electron collisions are believed to be the dominant cause of gas ionization. A theory is proposed to explain these measurements which predicts under special conditions an exponential increase in ion density. The fine structure may have its origin in the so called ‘‘ionization instabilities.’’ Gas ion currents of up to 2 A have been measured showing that the cathodic arc may be useful as a source of gas ions for assisting film deposition.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Tx Emission, absorption, and scattering of particles
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Intrinsic mechanism of smooth and rough morphology in etching of InP by Cl2 determined by infrared laser interferometry

M. Vernon, T. R. Hayes, and V. M. Donnelly

J. Vac. Sci. Technol. A 10, 3499 (1992); http://dx.doi.org/10.1116/1.577809 (8 pages) | Cited 16 times

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The effect of Cl2 pressure and substrate temperature (Ts) on the absolute, steady‐state etch rates of InP(100) has been measured with ∼1% accuracy from ∼0.02 to 1000 Å/sec by infrared laser interferometry. An unexpected finding was that the etch rate could exceed the calculated evaporation rate of InCl3 by a factor of 50, indicating a weaker binding energy of InCl3 to InP relative to itself. At sufficiently low Ts, the measured slow etch rate is only a factor of ∼3.5 above that predicted from the evaporation rate of InCl3. The transition between the fast and slow etch rates occurs as a first‐order phase transition at a substrate temperature, T∗s, which depends on the Cl2 pressure. If InP is etched at T∗s, the surface roughens while at other Ts the surface remains smooth. The explanation for the surface roughening is that at T∗s, InCl3 nucleates to form InCl3 islands. At T∗s the etch rate is approximately fifteen times slower where the InP surface is covered by InCl3 compared to the bare InP surface. The large differential etch rates for bare and InCl3 covered InP produces a rough surface morphology. Below T∗s, the surface is completely covered by an InCl3 multilayer and etches uniformly although slowly at the nominal InCl3 vaporization rate. This mechanism of surface roughening is intrinsic to the Cl2+InP reaction.    
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Temperature programming for isothermal desorption rate measurements

Michael A. DeAngelis and A. Brad Anton

J. Vac. Sci. Technol. A 10, 3507 (1992); http://dx.doi.org/10.1116/1.577810 (10 pages) | Cited 1 time

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We describe a digital feedforward/feedback controller for the implementation of rapid changes in the temperature of a small, resistively heated metal adsorbent in ultrahigh vacuum. The feedforward loop is based on a second‐order model of the system’s thermal response, modified by inclusion of a time delay to account for the characteristic time for heat conduction in the adsorbent, and the feedback loop includes proportional and derivative actions. These features allow the temperature of a nickel single crystal, 10 mm diameter and 1 mm thick, to be increased 80 K within approximately 4 s without overshoot, after which desorption rates can be measured at constant surface temperature with a mass spectrometer. The performance of the temperature controller and the advantages of isothermal data collection and analysis are demonstrated with CO desorption from Ni(110), for which the functional dependence of the rate on surface coverage at constant temperature identifies clearly the participation of a mobile precursor state in the desorption process.
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68.35.Md Surface thermodynamics, surface energies
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Hydrogen profiling by elastic recoil detection in microcrystalline germanium thin films

C. Godet, P. Roca i Cabarrocas, S. C. Gujrathi, and P. A. Burret

J. Vac. Sci. Technol. A 10, 3517 (1992); http://dx.doi.org/10.1116/1.577811 (5 pages)

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The elastic recoil detection technique improved by the time‐of‐flight is applied to the study of depth inhomogeneities in hydrogenated semiconductor thin films. The ex situ H profiling with a negligible H2O surface contamination (H surface peak) is made possible using a 300‐Å‐thick Al film evaporated on top of the sample. The H depth resolution is about 150 Å at the surface and is limited by straggling effects in the bulk. Microcrystalline germanium (μc‐Ge:H) thin films have been obtained at low temperatures (423 and 523 K) from the plasma enhanced chemical vapor deposition using GeH4 diluted at 0.27% in H2. An increase of the crystallinity of the μc‐Ge:H films vs distance to the substrate is observed. Depending on the deposition temperature, some films show a surface (300 Å) H content excess or depletion, attributed to effusion and trapping of molecular hydrogen into internal voids, during the deposition.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology

Energy resolved angular distribution of argon ions at the substrate plane of a radio frequency plasma reactor

Joachim Janes and Christoph Huth

J. Vac. Sci. Technol. A 10, 3522 (1992); http://dx.doi.org/10.1116/1.577779 (10 pages) | Cited 10 times

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The energy resolved angular distributions of argon ions of a 13.56 MHz rf discharge bombarding the powered electrode in a parallel plate reactor are investigated. Argon ions from the plasma are sampled through a small orifice in the powered cathode and are analyzed using a quadrupole mass spectrometer equipped with an energy filter. The angular resolution of the instrument is slightly better than 1°. The process pressure ranges from 5 to 50 mTorr and the rf power is varied to yield dc bias potentials between −100 and −450 V. The measured energy distributions of argon ions extend from 0 eV up to a maximal energy corresponding to the dc bias potential and exhibit significant structures which are explained by the effect of collisions in the sheath combined with rf modulations of the sheath potential. The principle structures in the ion energy distributions are nearly independent from the angle of ion trajectories with respect to the electrode normal. The energy resolved ion angular distributions are investigated in the range between ±3° and show structures which may be resulting from charge exchange collisions and elastic scattering of ions in the sheath. Angular distributions centered around the surface normal are found with angular widths between 1° and 2°. Furthermore, extrema at angles between 1° and 2° are detected for distinct energies and plasma parameters.
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52.80.Vp Discharge in vacuum
52.25.Tx Emission, absorption, and scattering of particles
81.65.-b Surface treatments

Measurement of the elemental composition of a‐SiC:H films by electron spectroscopy and high energy ion scattering spectrometry

M. J. Loboda, S. Baumann, M. J. Edgell, and K. Stolt

J. Vac. Sci. Technol. A 10, 3532 (1992); http://dx.doi.org/10.1116/1.577780 (8 pages)

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Amorphous hydrogenated silicon carbide (a‐SiC:H) thin films were deposited at low (175 °C) and medium (600 °C) temperatures using plasma enhanced chemical vapor deposition. By variation of the precursor gases, a broad range of film stoichiometry was obtained. The a‐SiC:H films were characterized by electron spectroscopy [x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES)], high energy ion scattering spectrometry [Rutherford backscattering spectrometry (RBS), elastic recoil detection], and ellipsometry. Quantitation of the carbon to silicon ratio was performed using elemental sensitivity factors in electron spectroscopy and compared with the inherently quantitative values obtained by RBS. The discrepancy between XPS and RBS was 5%–10%. The discrepancy between AES and RBS was significantly worse, but could be reduced to the same range as XPS with the use of an appropriate standard material. It was observed that ion beams typically used in sputter depth profiling did not result in significant preferential sputtering in the a‐SiC:H films, but those used in ion scattering measurements can modify films with large hydrogen concentrations. Calculations of film thickness from the ion scattering data showed excellent agreement with results obtained from ellipsometry.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.Nq Composition and phase identification

Particulate release from surfaces exposed to a plasma

J. Goree and T. E. Sheridan

J. Vac. Sci. Technol. A 10, 3540 (1992); http://dx.doi.org/10.1116/1.577781 (5 pages) | Cited 6 times

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Contamination can occur during plasma processing when micrometer‐size particulates fall from vacuum vessel walls onto a wafer. In situ light‐scattering measurements show how particulates are shed from walls. Using a test surface coated with micron‐size particles, we find that when a plasma is turned on, particulates are released rapidly, and when it is turned off, this release stops. This proves that plasma exposure causes particulate shedding. The rate of dust shedding increases with plasma density. The inventory of dust on the surface decays exponentially in time, with a time constant ≊102 s in our experiment, for plasma densities of ≊1014 m−3. Particulates become negatively charged due to the flux of electrons and ions onto the surface and are then pulled off the surface by the electric field in the plasma sheath. An individual dust grain is shed when its charge Q becomes sufficiently negative.
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52.40.Hf Plasma-material interactions; boundary layer effects

Understanding surface activity of oxides from oxide–metal interface formation

S. M. Mukhopadhyay and C. S. Chen

J. Vac. Sci. Technol. A 10, 3545 (1992); http://dx.doi.org/10.1116/1.577782 (5 pages) | Cited 4 times

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We propose a technique to estimate the concentration of reactive oxidation sites on an otherwise nonreacting oxide surface; it involves evaporating submonolayer amounts of a nonreacting metal on the oxide and carefully analyzing the fraction that undergoes chemical bonding, using x‐ray photoelectron spectroscopy. In this report, Ni has been evaporated on alumina, magnesia, and silica surfaces, and the growing Ni 2p photoelectron peak carefully monitored. It was observed that during the initial stages of bonding, a fraction of the first monolayer of Ni undergoes oxidation to form NiO. This oxidized component grows initially and then saturates to a certain level. This saturation level, expressed as a fraction (Θ) of the first monolayer, can be used as a measure of oxygen‐active sites such as unattached oxygen bonds. We found that on epitaxially polished sapphire, Θ was as high as 20% of a monolayer. It was considerably reduced when the surface was sputtered with Ar+ ions in vacuum, a process which is known to create an oxygen‐deficient Al2O3 surface. In MgO crystals (which do not tend to lose oxygen on ion sputtering), Θ remained practically unchanged. Such observations confirm the feasibility of using this technique as a probe for surface oxygen activity. It was found that increased level of dissolved magnesia in the sapphire lattice reduced the fraction of oxidized component. On the other hand, excessive doping with MgO (which leads to second phase spinel precipitates) seems to increase it considerably. The former observation is attributed to defect chemistry of the corrundum lattice and the latter has been discussed in light of earlier mass transport measurements. Silica surfaces were found to offer negligible oxidation sites, irrespective of sample history. Using this technique, one can systematically study how the concentration of reactive sites (which determines the amount of interfacial bonding) will be influenced by surface modifications.
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68.35.Md Surface thermodynamics, surface energies

Electrical characterization of radio‐frequency discharges in the Gaseous Electronics Conference Reference Cell

Mark A. Sobolewski

J. Vac. Sci. Technol. A 10, 3550 (1992); http://dx.doi.org/10.1116/1.577783 (13 pages) | Cited 47 times

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Measurements of the electrical characteristics of radio‐frequency (rf) discharges can be subject to large errors due to limitations in the measurement instruments and the stray impedance of the discharge cell. This study reports electrical measurements of argon discharges in the GEC Reference Cell in which special care has been taken to identify and minimize these sources of error. Careful calibration of current and voltage probes was found to be essential. In addition, parasitic impedances in the cell were found to be large, sensitive to minor changes in electrical connections, and not adequately described by simple a priori models. A general technique for characterizing the stray impedance, including an analysis of the propagation of errors, is presented here. This technique assures accurate results with specified uncertainties. Error analysis demonstrated that large gains in the precision of the measurements can be obtained using an inductive shunt circuit. Together, these techniques should improve the utility of electrical measurements for gauging the reproducibility of plasma conditions among rf discharge cells, for testing theoretical results, and for monitoring plasma processing.
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52.70.Ds Electric and magnetic measurements
52.80.-s Electric discharges

Study of the performance of a group of quadrupole mass spectrometers

W. E. Austin, J. H. Leck, and J. H. Batey

J. Vac. Sci. Technol. A 10, 3563 (1992); http://dx.doi.org/10.1116/1.577784 (5 pages) | Cited 1 time

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Results are presented from a series of experiments that were designed to characterise quadrupole analyzers. Three different analyzers have been studied. The first, typical of the small quadrupoles often used for residual gas analysis, has rods 50 mm long and 6.25 mm in diameter. The second uses rods of similar diameter, but 125 mm long. The third uses rods of diameter 12 mm and length 230 mm. Simple ion sources were used. All had cylindrical ionization regions with external filaments, in a configuration similar to an extractor ion gauge. All were operated under similar conditions. The sensitivity and linearity of the instrument is found to depend in a complex way on the operating conditions of the ion source. The observed behavior is explained qualitatively by the presence of both electronic and ionic space charge in the ion source.
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07.75.+h Mass spectrometers

Design and development of a vortex amplifier for pressure regulation of glove boxes

M. G. Balakrishnan, K. N. Mahule, and Surya Narayan

J. Vac. Sci. Technol. A 10, 3568 (1992); http://dx.doi.org/10.1116/1.577785 (5 pages)

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Vortex amplifiers are fluidic devices which can be used for pressure regulation of glove boxes, radioactive cells, and other similar ventilated enclosures. This article describes the design and development of a vortex amplifier for use as a pressure regulator for glove boxes in which radioactive materials are handled. The vortex amplifier has several advantages over other types of pressure regulators like fast response, no electrical power supply, no friction or inertia as in the case of valves, and no mechanical moving parts.
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07.30.Hd Vacuum testing methods; leak detectors
06.60.-c Laboratory procedures

Low voltage and high speed operating electrostatic wafer chuck

Mamoru Nakasuji and Hiroyasu Shimizu

J. Vac. Sci. Technol. A 10, 3573 (1992); http://dx.doi.org/10.1116/1.577786 (6 pages) | Cited 1 time

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A new electrostatic force expression for the electrostatic wafer chuck with a three layer insulator is introduced. If a few micrometers of air layer is assumed, the expression coincides with the experimental results. An electrostatic wafer chuck with a two layer insulator is designed and evaluated. The bottom layer is a spin coated polyimide and the top layer is a vacuum evaporated alumina. The holding pressure is 35 gf/cm2, when 200 V dc is applied in atmosphere. The pressure is not influenced by the duration of the applied voltage. The residual pressure, after the voltage is turned off, decreases to zero rapidly. The breakdown voltage is from 320 to 700 V. The scratch test shows good results due to a vacuum evaporated alumina layer.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Large, all‐metal‐sealed, vacuum gate valve for fusion application

Thomas H. Batzer, Dwight D. Lang, and Ralph W. Moir

J. Vac. Sci. Technol. A 10, 3579 (1992); http://dx.doi.org/10.1116/1.577787 (5 pages) | Cited 3 times

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Two large (30 cm and 1 m in diameter), innovative, fusion‐reactor‐compatible, vacuum gate valves have been developed which should contribute significantly to the vacuum hardware needs of the next‐generation, tritium‐burning fusion devices. Because no organic materials are used, the valves are tritium‐compatible and radiation‐hardened as well as compatible with toxic gases. These valves should also find applications in semiconductor manufacturing and in similar industries that have requirements for large, all‐metal vacuum valves. We have designed, built, and successfully tested a 30‐cm‐diam valve, and we have designed and are fabricating a 1‐m‐diam valve that we plan to assemble and test in 1992. This work makes use of the all‐metal‐sealed, radially directed, fluid‐pressure‐loaded seal design that was developed under a Department of Energy contract at the Lawrence Livermore National Laboratory. This seal, due to its radially directed loading, is easily scaled to larger diameters, and scales with the atmospheric loading of the gates, rather than with the seal loading. The valves are designed for high reliability: the 30‐cm‐diam valve utilizes double gates to provide two seals, and differential pumping; the 1‐m‐diam valve has a single gate with a double metal seal, and differential pumping. These valves are relatively light weight due to the unique radial seal. Typically, leak‐tight closures are obtained on every operation without differential pumping at pressures of 500–1000 psi applied to the radially sealing diaphragm. The seal components are fabricated from 304 stainless steel, but can also be made from aluminum.
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28.52.Lf Components and instrumentation
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Seed cone evolution on positively charged Cu targets: Preliminary study by high‐resolution electron microscopy

Y. Mori, Y. Fujimoto, and F. Okuyama

J. Vac. Sci. Technol. A 10, 3584 (1992); http://dx.doi.org/10.1116/1.577788 (4 pages) | Cited 2 times

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The electrostatic effect on the seed cone evolution at Ar+‐bombarded Cu(111) surfaces was investigated by means of high‐resolution transmission electron microscopy. A simultaneous supply of Mo seeds to the target biased at positive 100–150 V was found to induce an oriented growth of nanometer thick Mo layers on the cone slopes receiving high seed fluxes. In the seed layers thus grown, Mo atoms were so arranged that Mo〈100〉 was parallel with the ion‐incidence direction, suggesting that depositing Mo atoms were forcibly stacked very close to one another along the ion beam, by a strong electrostatic field generated at the growth front of seed layer. Evidence is also presented that the seed layers were grown via a particle supply process of Kossel type.
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81.15.Cd Deposition by sputtering

Improvement in the reliability of hot‐cathode ionization tube calibration by the use of benchmark tubes

G. F. Vanderschmidt

J. Vac. Sci. Technol. A 10, 3588 (1992); http://dx.doi.org/10.1116/1.577789 (2 pages)

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07.30.Dz Vacuum gauges
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