Browse - Journal of Vacuum Science & Technology Archives 1964-1982

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Calculation of Deposition Uniformity in rf Sputtering

I. Brodie

J. Vac. Sci. Technol. 6, 795 (1969); http://dx.doi.org/10.1116/1.1492710 (6 pages) | Cited 3 times

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Assuming a uniform flux of ions upon the target, a cosine distribution of sputtered material, unity sticking coefficient on the substrate, no surface mobility and no gas collisions, deposition uniformities are calculated for several device configurations. These include: (1) the “peak” configuration of adjacent rectangular targets, (2) the disk type, and (3) coaxial cylindrical targets and substrate holders. Areas over which the deposition uniformities are predicted to be within ±1% to ±10% were computed and these results compared with available experimental results obtained from rf sputtering devices. The good agreement obtained shows that the method does give a practical approach to estimating deposition uniformities for rf sputtering systems where the assumptions are reasonably well obeyed. The peak configuration is examined in some detail and it is found that there is an optimum position for the substrate table at which the largest, area of uniform deposition is obtained.

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79.20.Rf

Atomic, molecular, and ion beam impact and interactions with surfaces

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Accurate Pressure Measurements in the Region 0.1–1000 mTorr; The Intercalibration of Two McLeod Gauges and a Capacitance Manometer

J. Philip Bromberg

J. Vac. Sci. Technol. 6, 801 (1969); http://dx.doi.org/10.1116/1.1492711 (8 pages) | Cited 14 times

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The capacitance manometer appears to be a convenient and reliable pressure measuring device over the range 0.1–1000 mTorr. We find that deviations from linearity in this region do not exceed a few tenths of a percent. On the other hand, mercury streaming in a trapped McLeod gauge can introduce errors in the measured pressures which are dependent upon the pressure in a complicated manner.

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07.30.Dz

Vacuum gauges

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Interface and Adhesion Studies of Evaporated Se on Oxide Surfaces

Yuen-Sheng Chiang and Samuel W. Ing

J. Vac. Sci. Technol. 6, 809 (1969); http://dx.doi.org/10.1116/1.1492712 (6 pages)

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Adhesion of evaporated amorphous Se on oxide surfaces has been studied. For selenium evaporated in a relatively poor vacuum of 10⁻⁵ Torr onto aluminum substrates coated with a surface oxide layer, the Se deposit could easily be peeled off the substrate. Electron microscope examination of the separated surfaces showed that the separation, in general, occurred at or in the immediate vicinity of the Se-aluminum oxide interface. Complimentary studies were also conducted on Se evaporated onto oxide substrates in an ultra-high vacuum system. Substrates used were single crystals of sapphire and MgO and virteous quartz. Experimental observations indicated that the relative strength of adhesion and the fractured surface features were dependent on and could be correlated with the substrate preheat temperaure in a high vacuum prior to Se evaporation. With a sufficiently high preheat temperature, the interfacial bond strength exceeded that of the cohesive energy of Se and the failure occurred in the Se layer. Studies on the effect of chemisorbed gas species on adhesion showed that water absorption does not degrade the strength of the Se-oxide structure. However, absorption of long chain organic acids and alcohols on the substrate surface resutled in poor adhesion strength, and the failure occurred at the interface region.

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68.35.-p	Solid surfaces and solid-solid interfaces: structure and energetics
81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy

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In Situ Transmission Electronmicroscopic Study of Crystal Growth by Chemical Vapor Deposition

Thomas Gabor and John M. Blocher

J. Vac. Sci. Technol. 6, 815 (1969); http://dx.doi.org/10.1116/1.1492713 (13 pages) | Cited 3 times

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A gas-reaction chamber has been constructed, which allows the in situ transmission electronmicroscopic study of gas-solid reactions at temperatures up to 900 °–1000 °C. The morphological and crystallographic properties of iron, of iron and wüstite, and of magnetite depositing epitaxially on (111) gold substrates, either by the thermal decomposition of Fe(CO)₅ or by decomposition and chemical reaction from Fe(CO)₅–H₂ or from Fe(CO)₅–H₂–H₂O mixtures, are described. In other examples, the oxidation of the initially depositing iron is illustrated. In some of the experiments, polycrystalline iron foils were substituted for the (111) gold substrates, and a profound effect of iron deposition on the rate of grain growth in the iron foil was found. Coalescence of iron crystallites and high mobility of the deposit were observed. Incidental observations on the decomposition of Ni(CO)⁴ are described. These permit comparison of the epitaxial relationships in the Ni–Au and NiO–Au systems with those of the corresponding iron systems.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Hk	Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp	Transmission electron microscopy (TEM)

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Errata: “Nonequilibrium Chemical Reactivity of Polycrystalline Iron Foils”

T. Gabor and J. M. Blocher

J. Vac. Sci. Technol. 6, 827 (1969); http://dx.doi.org/10.1116/1.1492714 (1 page)

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73.20.Mf	Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.65.Mq	Oxidation
99.10.Cd	Errata

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Electroluminescence, Bistable Switching, and Dielectric Breakdown of Nb₂O₅ Diodes

T. W. Hickmott

J. Vac. Sci. Technol. 6, 828 (1969); http://dx.doi.org/10.1116/1.1492715 (6 pages) | Cited 23 times

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Nb–Nb₂O₅–metal diodes, after voltage breakdown, exhibit current-controlled negative resistance and switching between two stable conduction states. Before breakdown, Nb–Nb₂O₅–Au diodes are electroluminescent with hole injection occurring at the Nb₂O₅–Au interface. After breakdown, electroluminescence is closely related to switching. The energy of emitted radiation has maxima at 1.3 and 1.6 eV. Electroluminescence is both polarity- and voltage-dependent, indicating that hole injection, not heating, produces electroluminescence. Increased electroluminescence accompanies diode switching. Microscopic observation shows that bistable switching and dielectric breakdown of Nb–Nb₂O₅–Au diodes occur at small conducting regions in the oxide. Destructive dielectric breakdown in Nb–Nb₂O₅–Cu diodes differs from that in Nb–Nb₂O₅–Au diodes.

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73.40.Rw	Metal-insulator-metal structures
78.60.Fi	Electroluminescence
77.22.Jp	Dielectric breakdown and space-charge effects
77.55.-g	Dielectric thin films

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Motion of Liquid Films on Metal Surfaces in High Vacuum

L. P. Levine and James Landowski

J. Vac. Sci. Technol. 6, 834 (1969); http://dx.doi.org/10.1116/1.1492716 (4 pages)

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Observations have been made on the motion of thin films of oil on polycrystalline tungsten surfaces at pressures of the order of 10⁻⁶−10⁻⁸ Torr. Measurements were made by utilizing the difference in secondary electron coefficient between a clean and an oil-covered surface. The apparatus is discussed. Propagation velocities of films of Octoil-S and Dow Corning 702 are presented for surface temperatures between 230 and 310 K. The implications of this motion are discussed.

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68.08.Bc	Wetting
07.30.-t	Vacuum apparatus

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Effects of Added O₂ upon Argon Emission from an rf Glow Discharge

J. B. Lounsbury

J. Vac. Sci. Technol. 6, 838 (1969); http://dx.doi.org/10.1116/1.1492717 (5 pages) | Cited 5 times

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Emission and absorption measurements have been made in rf glow discharges through pure argon and through argon with 1% O₂ added. The results indicate that added O₂ reduces the amount of excitation of neutral argon, particularly the concentration of metastable atoms. At the same time, increased emission is observed from argon ions when O₂ is added. This is attributed to an increase in the argon ion concentration. The results of these experiments have important implications regarding the mechanisms operative in rf sputtering processes. Namely, under the conditions studied (rf power density of 10 W∕cm² and argon pressure 4×10⁻² Torr) direct electron impact ionization appears to be the predominant maintenance mechanism of the glow rather than ionization resulting from metastable atom collisions. In addition, it is proposed that addition of oxygen to the argon discharge atmosphere serves to increase the secondary electron emission coefficient of the fused silica target.

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52.80.Pi	High-frequency and RF discharges
52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.77.Bn	Etching and cleaning
52.77.Dq	Plasma-based ion implantation and deposition
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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AC Impedance of Space-Charge Barriers

J. Maserjian

J. Vac. Sci. Technol. 6, 843 (1969); http://dx.doi.org/10.1116/1.1492718 (5 pages) | Cited 9 times

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The ac impedance has been considered in a general way which includes the effect of a distribution of trapping states within Schottky-type energy barriers. Starting with the complete unipolar transport equation, and introducing a density-of-trapping-states function, depending generally on both position and energy, one arrives at a useful formulation of the ac impedance. This result is possible because of the rapid variation of the effect of traps in such barriers which restricts their main contribution to a narrow range of positions and energies. Thus, expressions are obtained which relate the ac impedance measurements to the trapping effect at regions of the barrier corresponding to the applied frequency, voltage, and temperature. With these three independent variables, it is possible to experimentally scan the barrier over energy and position, obtaining a profile of trap densities and other barrier properties as well as independent tests on the selfconsistency of the method. Some experimental results obtained from thin-film Nb₂O₅ capacitors are given and shown to be in general agreement with the theory. This agreement also supports our contention, based on previous dc studies, that the Nb₂O₅ film contains a large ionic space charge. From the results we calculate a barrier minimum of 0.38 eV, an average trap density of about 10¹⁹ cm⁻³ eV⁻¹, and trap capture cross section of about 10⁻¹³ cm².

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73.30.+y	Surface double layers, Schottky barriers, and work functions
77.22.Jp	Dielectric breakdown and space-charge effects
77.55.-g	Dielectric thin films

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The Sensitivity of Bayard–Alpert Gauges

P. A. Redhead

J. Vac. Sci. Technol. 6, 848 (1969); http://dx.doi.org/10.1116/1.1492719 (7 pages) | Cited 3 times

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The sensitivity of Bayard–Alpert gauges has been measured as a function of the grid-filament spacing and found to vary by as much as a factor of 2.5. It is suggested that the large variation of sensitivity from one gauge to another results from variability of filament positioning. An hypothesis is proposed, and substantiated by test, which relates the sensitivity to the angular momentum, about the axis of the grid, with which electrons are launched into the grid. It is shown that electrons with small initial angular momentum have the longest orbits in the useful ionizing volume. A new type of Bayard–Alpert gauge has been developed, based on this hypothesis, whose sensitivity is independent of filament position and of the potential of the envelope. The sensitivity factor of this new design is about 55 Torr⁻¹ for nitrogen.

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07.30.Dz

Vacuum gauges

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Solid Amorphous Bi, Ga, and Fe as Examples of Liquid-Like Amorphous Substances

H. Richter

J. Vac. Sci. Technol. 6, 855 (1969); http://dx.doi.org/10.1116/1.1492720 (4 pages) | Cited 1 time

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Experiments show that two structures simultaneously occur in liquid-like solid amorphous and in molten Bi and Ga, i.e., the spherical close packing in the form of a straight atomic chain and the layer lattice structure. In Bi the layer lattices are derived from the respective lattice and in Ga they are remainders of the lattice. In solid amorphous Fe the spherical close packing shows up as a zigzag chain in the atomic distribution curve as in molten Na. Differing from Bi and Ga, in amorphous Fe the layer lattices are parts of the lattice.

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61.43.Dq	Amorphous semiconductors, metals, and alloys
61.25.Mv	Liquid metals and alloys

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Response of a Heated Thermocouple Vacuum Gauge in Air and Parylene Systems

M. A. Spivack, D. B. Anderson, and L. L. Carpenter

J. Vac. Sci. Technol. 6, 859 (1969); http://dx.doi.org/10.1116/1.1492721 (6 pages) | Cited 1 time

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The pressure of a condensible gas such as di-p-xylylene (parylene dimer) or p-xylylene (parylene monomer) may be determined by using a heated thermocouple gauge to retard absorption or polymerization on the gauge elements. An equation has been derived which relates the voltage response of a compensated thermocouple gauge to the true pressure of the system at gauge operating temperatures in the range 25 °–300 °C. Correlation of data and theory have been found using air as a standard reference. Semi-empirical curves fitted to the data for parylene diradical (monomer) shows that the specific heat calculated from the derived equation agrees with theoretical expectations. The specific heats calculated from parylene dimer curves show these values to pass through a maximum at 400 °–450 °C. This corresponds to an inflection point in the gauge response curve and also to the conversion temperature of parylene dimer to parylene monomer.

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07.30.Dz

Vacuum gauges

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Anisotropic Film Growth and Pseudomorphism of Silver on a Germanium (110) Surface

R. Wübbenhorst, K. Hartig, and R. Niedermayer

J. Vac. Sci. Technol. 6, 865 (1969); http://dx.doi.org/10.1116/1.1492722 (6 pages)

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Ag films were evaporated under clean conditions onto a Ge (110) surface, in order to investigate the growth of a film of high misfit on an anisotropic surface. The structure of the resulting films was analyzed with LEED. The films grew in the form of three-dimensional islands in parallel orientation to the substrate. They showed up to 20% distortion in the [001] direction and no distortion in the [110] direction. At the same time the islands were narrow in [001̄] and elongated in [1̄10]. This connection of unidirectional pseudomorphism and anisotropic islands form is in qualitative agreement with previous theoretical considerations.

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