Vacuum evaporator for ultra-high vacuum fabrication of multilayer devices

Vacuum evaporator for ultra-high vacuum fabrication of multilayer devices

Classified abstracts 452--461 The installation has been worked out by the Kiev Polytechnic Institute and has proved economic and effective for purifyi...

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Classified abstracts 452--461 The installation has been worked out by the Kiev Polytechnic Institute and has proved economic and effective for purifying metals from admixtures. The structure of the electron gun and its focusing device are illustrated. The working pressure in the chamber is 10 -4 to 10 -5 torr, power of rectifier 3.5 kV, current 100 to 150 mA and voltage 2-27 kV. Anon, Powder Metallurgy, (3), 1964, 91-94, (in Russian).

III. Vacuum applications 30. Evaporation and sputtering 30 The sticking coefficient, the optical transmission and the oxidation of thin metallic films. See abstract number 411. 30 Preparation and properties of electro-luminescent ZnS:Cu, Mn, C! films. See abstract number 426. 30 Ion bombardment and its effect on the optical properties of metals. See abstract number 485. 30 Deposition and monitoring apparatus for preparing passive microcircuits. See abstract number 510. 30 : 16 : 52 452. Heterogeneous recombination of atomic gases. Interaction of hydrogen atoms with a molybdenum surface. (USSR) Experiments on the kinetics of interaction of hydrogen atoms (generated in a high voltage discharge tube) with a pure molybdenum surface were carried out at a temperature range of 100850°C. The atomic concentration in the discharge tube was 10 per cent and the partial pressure of the atomic hydrogen in the system ranged from 5 × 10-3-5 × 10 -2 torr. The recombination coefficients for various gas pressures and temperatures were calculated from the experimental results. It is pointed out that reactions of this kind occurring near the surface of a space vehicle travelling at high speed may have a considerable effect on skin temperature and heat transfer. The presence of shock waves will complicate the process. V A Lavrenko and I N Frantsevich, Space Research, 111 (1), 1965, 135-141, (in Russian). 30 : 37 453. High temperature vaporization studies with the Bendix time-offlight mass spectrometer. (USA) The mass spectrometer used in these experiments was capable of monitoring up to 6 species simultaneously as well as presenting a scope trace of the mass spectrum. The electron bombardment furnace was specially built for the spectrometer. At maximum power a bombarding current of 500 mA is achieved. Among the reactions studied with this equipment were the decomposition of solid uraniumn itride and the reduction of uranium tetrafluoride with magnesium vapour. R W Bonham et al, Trans 6 Vac Metall Conf, American Vacuum Society, 1964, 140-147. 30 : 33 : 4l 454. The growth and structure of gold and silver deposits formed by evaporation inside an electron microscope. (Great Britain) The authors' experiments provide detailed information on the mode of growth of single crystal films of gold and silver. Direct observation shows a remarkable liquid-like behaviour of the coalescence of the initial nuclei leading to the formation of a continuous film. Various possible mechanisms for this phenomenon are discussed. D W Pashley et al, Phil Mag, 10, July 1964, 127-158. 30 : 41 455. Proton space charge in anodie oxide films. (Great Britain) The capacitance of anodic oxide films on niobium, tantalum, titanium and antimony depends very markedly on the PD applied to the film during measurement. Similar films deposited on aluminium, beryllium, gallium, zirconium, bismuth and silicon show no such effect. The increase in capacitance with decrease in PD for films of the first category is attributed to proton space charge within the film. D A Vermilyea, J Phys Chem Solids, 26 (I), Jan 1965, 133-142.

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30 : 37 : 4! 456. Evaporation of elements from 80/20 nickel-chromium during vacuum induction melting. (USA) Fifteen kilogram melts of 80 per cent nickel-20 per cent chromium, containing approximately 0.1 per cent of the element under study, were held under a vacuum of 10 -3 to 10 -2 torr, at 2850°F for times up to two hours. Samples were periodically taken and subsequently analyzed. The results are presented as a semi-logarithmic plot of concentration versus time for the elements lead, bismuth, tin, arsenic, antimony, selenium, and copper, while the concentration of arsenic, tin, and antimony in the melt remained constant. The melts to which arsenic or antimony had been added showed a large negative deviation from Raoult's law. The melt to which copper had been added showed a positive deviation from ideality. (USA) P P Tnrillon, Trans 6 Vac Metall Conf, American Vacuum Society, 1964, 88-102. 3O 457. Sputtering mechanisms. (USA) The current state of knowledge of sputtering mechanisms is indicated through a discussion of several important aspects of sputtering phenomena currently being investigated in our laboratory. The main topics considered are (1) sputtering thresholds, (2) sputtered atom ejection patterns and velocities, (3) the sputtering of compounds, and (4) sputtered thin films. Recent experimental and theoretical approaches to sputtering are also discussed. S P Wolsky, Trans IO A VS Nat Vac Syrup, MacMillan & Cop 1963, p 309. 3O 458. Some properties of sputtered sulphide films. (USA) Sulphide films of cadmium, lead, copper, tin and molybdenum have been deposited by reactive sputtering. Stable, uniform films, over 50 cm 2 in area, have been formed in this manner. Cadmium sulphide films were studied extensively. Typical dark resistivity was 10-~-10 8 ohm cm. On doping the films during deposition a high degree of photoconductivity was induced. Wide variations in film properties were also produced by varying the stoichiometry of the sulphide during film formation. Photovoltaic elements were formed by providing the CdS film with a metal contact. Temperature coefficients of photo resistance, spectral transmittance, and photovaltaic spectral response were measured. The absorption edge was found to lie around 5000/k. T K Lakshmanan and J M Mitchell, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963,p 335. 30 : 10 459. A high capacity vacuum sputtering machine. (USA) The design objective for this machine was to be able to sputter tantalum uniformly onto large area glass substrates (36 sq in. each), and to be able to process a large number of substrates with one pump-down of the vacuum system. This machine is intermediate in production capacity between that reported by (1) Altman and (2) Isaak, and that reported by (3) Charschan and Westgard. The ultimate vacuum obtainable is 5 × 10 9 torr within a chamber containing 540 sq in. of glass substrates. Higher sputtering rates and better uniformity are achieved than have been reported previously. J G Needham, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963, p 402. 30 : 26 460. Vacuum techniques for fabricating integrated cryoelectrie computer devices. (USA) The fabrication requirements for integrated multilayer cryoelectric and magnetic computer devices are becoming difficult to meet by conventional approaches. This paper describes some unusual techniques particularly suited to making these more difficult devices. A high precision twelve-position mask changer is detailed that includes crystal film thickness monitoring for all positions and accurate alignment of the masks and substrate. The masks are mounted on frames and tested for accurate alignment before installation in the vacuum chamber. A special procedure is used to prevent pinholes in insulation layers the details of which will be described. G W Leek, Trans I0 A VS Nat Vac Syrup, MacMillan & Co, 1963, p 397. 30 : 56 461. Vacuum evaporator for ultra-high vacuum fabrication of multilayer devices. (USA)

Classified abstracts 462--469 A n evaporator has been built for use in a bakeable, oil free, ultrahigh vacuum chamber which permits multilayer thin-film devices of three metals and one dielectric to be made. Problems due to high friction in the clean chamber are circumvented through the use of bellows which allow movement and registration fixtures to be exterior to the vacuum chamber. These fixtures may be removed during bake and lubricated while in use. Currently, four substrates (3/4 in. × 3/4 in.) and four different evaporation masks are being used. However, with smaller substrates masks may be employed. Cross contamination of evaporation sources is minimized through the use of removable covers and evaporation rates are controlled with an ionization gauge monitor. Results on trapped flux in lead films obtained on devices fabricated in this system are also discussed. H L Caswell, Trans 10 A V S Nat Vac Symp, MacMillan & Co, 1963, p 393. 30 : 41 462. The microstrueture and some related electrical properties of tantalum films. (USA) Examination of tantalum films by electron microscopy showed the presence of particles with dimensions which were sensitive to the deposition temperature. Particles of 100-200/~, diameter condensed initially. Further clustering occurred as film thickness increased. Higher substrate temperatures ultimately resulted in the formation of coarse crystalline agglomerates with diameters of the order of one micron. Corresponding changes in electrical properties were observed. A relation between particle size and electrical properties was demonstrated, System pressures ranging from 10 -7 to 10 -1° torr were employed. Mass spectrometric analyses were made to study composition of the residual atmosphere as a function of working pressure and heating surfaces. N J Maskalick et al, Trans 10 A V S Nat Vac Syrup, MacMillan & Co, 1963, p 503. 30 : 56 " 41 463. The preparation and properties of silicon monoxide capacitors on passivated silicon substrates. (USA) The compatibility of silicon monoxide capacitors with the small geometry, processing requirements, and packaging requirements characteristic to the fabrication of the silicon integrated circuit has been explored and processes have been developed to produce reliable, low leakage units in the 0.12/zF/in. ~ range to predetermined value. The electron emission mechanism in the dielectric has been found to be primarily Schottky. The process reproducibility, along with the statistical distribution of the dissipation factor, leakage current, capacitance, and process yield, is presented. The results of load life evaluation at elevated temperatures and voltage stress are summarized. E R Dean, Trans IOA VS Nat Vac Syrup, MacMillan &Co, 1963,p485. 30 : 41 464. Thickness and composition of nickel-chromium films. (USA) Thin films of nickel-chromium were deposited on planar glass substrates by vacuum evaporation of the alloy "Nichrome V" with a nominal bulk composition: Ni 80 per cent-Cr 20 per cent. The nickel chromium ratio of deposited films was determined by chemical microanalysis (using spectrophotometric methods), the thickness by optical interferometry. The interdependencies of thickness t, composition ratio r, sheet resistivity P,, temperature coefficient of resistance a, film density 6, and other film parameters were investigated or derived and the interrelations of these variables are discussed. It is shown quantitatively how under constant evaporation and deposition conditions, the nickel-chromium composition ratio varies with the sheet resistivity r (p~) and how, on the other hand, the sheet resistivity varies with the thickness of those films, Ps(t). H J Degenhart and I H Pratt, Trans I0 A V S Nat Vac Syrup, MacMillan & Co, 1963, p 480. 30 465. Recent advances in vacuum evaporation of metals. (USA) Self-supporting films of A, Cu and Be up to 20 mils in thickness have been produced, which generally are ductile reproductions of the base on which they are deposited. Evaporation rates of the order of 0.5-1 gm per min per sq. in. of melt surface are possible. Refractory metals are best evaporated with the help of an electron beam. The tube between target and cathode is subdivided into a series of compartments which communicate through suitable

apertures. Each of the chambers can be separately pumped and it is thus possible to maintain a pressure of 10 -e torr at the cathode and 10 -1 torr at the target. By this technique metals such as molybdenum, tantalum, tungsten or palladium can be skull melted and vaporized without contaminating the melt with crucible components. A special facility was designed for the evaporation and handling of Be products on account of their toxic nature. Another area of study is concerned with the production of ultra-fine metal powders by evaporation and condensation at 10 tort. The powders are packaged in plastic bags and the purity of the commercial product is over 98 per cent. P J Clough and R W Steeves, Trans 6 Vac Metall Conf, American Vacuum Society, 1964, 167-175. 30 466. Vapour phase deposition of metals. ( U S A ) Vapour deposition methods are now being used commercially to produce semi-conductor grade silicon, elemental boron, hafnium crystal bar, nickel powder and shot and research quantities of high purity metals and compounds. The most noteworthy recent applications are the production of epitaxial diodes and of pyrolitic graphite parts. There has also been considerable development work on the coating of rocket nozzles with various refractory metals. The author discusses the basic principles involved in vapour deposition and considers in some detail the preparation of high purity metals and the tungsten coating of graphite rocket nozzles. R F Packard, Trans 6 Vac Metall Conf, American Vacuum Society, 1964, 176-185. 3O 467. The production of monocrystalline germanium films by evaporation in vacuum. (USSR) p-type germanium heated to 1100-1300 °C on a tungsten wire in a vacuum of 10 -5 torr was deposited on a substrate consisting of n-type germanium kept at a temperature of 400-650 °C. The films do not show up in a microscope and their presence is only detected by the change of sign of the thermo-electromotive force passing from substrate to film. X-ray analysis of the films revealed weak Debye lines of germanium in addition to the Laue spots characteristic of monoerystals. Optimum rate of deposition was found to be of the order of one micron per minute, with a final thickness of 3-15 microns. L G Lavrenteva and I K Kovalev, Papers o f the scientific-technical conference on Radio-Day, Tomsk University Publication, 1964, 3-6, (in Russian). 30 : 41 468. A bridging phenomenon in growth of evaporated metal films. (USA) Single crystal films of the fcc metals gold, copper, silver and nickel have been prepared by evaporation onto cleavage planes of NaC1 formed by cleaving salt crystals in vacuum at 200-400°C. During the early stages of growth, when muclei are 50-100/~ in size, many of the muclei become interconnected by bridges of metal, which often span distances as large as 100/~. The bridges constitute a mechanism of intergrowth of muclei before the stage at which actual contact of the muclei would occur. The bridging mechanism is believed to be related to decreased mobility of atoms and clusters on this type of substrate, and is highly dependent on substrate surface condition and temperature, and evaporation rate. R F Adamsky and R E LeBlanc, Trans 10 A V S Nat Vac Symp, MacMillan & Co, 1963, p 453. 30 : 56 469. Low leakage thin film capacitors. ( U S A ) One aspect in the microminiaturization of analog computer circuits is the low dc leakage current levels required of thin film capacitive components. To achieve leakage levels less than a nanoampere at the desired operating conditions, dielectric materials other than SiO were investigated. These materials included MgF2, and Alz08. Considerations such as fabrication ease, number of shorted units, and other electrical parameters led to the use of SiO in conjunction with a thinner film of the lower vapour pressure materials. The properties of these various film combinations are given including engineering data on SiO-SiOz evaporated film capacitors. R A Rossmeisl and F M Uno, Trans 10 A VS Nat Vac Symp, MacMillan & Co, 1963,p 449.

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