Patent GB-732891-A (GB)
Title: Improvements in and relating to the production of thin layers of chemical compounds on surfaces
IPC: C23C14/00
Filed: 1949-03-25
Abstract: 732,891. Coating by vapour deposition. MEGATRON, Ltd., VESZI, G. A., and MARKUS, P. March 22, 1950 [March 25, 1949], No. 8191/49. Class 82 (2). [Also in Groups XI, XV, XX, XXXVI and XL (a)] A process for the production upon a support, such as glass, of a transparent and strongly adnerent layer of at least one chemical compound containing a metal comprises subjecting the surface of the support to a discharge between a cathode and an anode, the support being placed on the anode and the cathode being composed of a material including the metal, and the discharge taking place in an atmosphere including a gas of high sputtering speed and a gas which reacts with the metal to produce the compound, the concentration of the reactive gas being controlled so as substantially to avoid the deposit in the compound of the free metal. A metallic layer may be afterwards deposited upon the layer of the compound. The gas of high sputtering speed may be one of the rare gases such as argon, forming not less than 5 per cent and not more than 95 per cent of the atmosphere in which the discharge takes place. A mixture of 6 per cent by volume of oxygen and 94 per cent of argon is referred to in the Provisional Specification. The reactive component of the atmosphere may be an element such as oxygen or a compound such as water vapour, sulphuretted hydrogen or an oxide of nitrogen, or air. The presence of nitrogen in the gas mixture will slow down the sputtering process if present in a high concentration. The cathode may be subjected to a preliminary discharge in an atmosphere which includes a reactive gas such as air or water vapour before the compound is deposited on the support, which atmosphere may contain a greater proportion of reactive gas and a lesser proportion, which may be negligible, of the gas of high sputtering speed than the atmosphere in which the second discharge takes place. Both atmospheres may contain the same reactive gas. The cathode may be formed of, or from, a substantially pure metallic element such as cadmium. There may be produced upon the support, in addition to the metal compound, a further metal or a further metal compound, the cathode being composed of an alloy of the metals or built up of parts of the metals. Cathodes of tin, antimony, bismuth or alloys or composite structures thereof are referred to. The cathode may have a surface composed of a chemical compound, a mixture of compounds or a mixture thereof with an element or elements. The process can be carried out by the apparatus shown in the drawing which comprises an opentop sputtering chamber 10 with a removable lid 11, both being of steel and having engaging surfaces which are carefully lapped so that with moderate greasing adequate vacuum sealing can be obtained. The chamber is double-walled to provide a water jacket. Insulatedly supported from the lid 11 is the sputtering cathode assembly 15 comprising a water-cooled hollow steel body 15a and a metal disc 15b. The lid 11 and the cathode assembly 15 are preferably mounted on a spring-balanced lever or on counter-weights to facilitate removal. A plate 18 on which are placed articles to be treated has apertures 19 which lead to an exhaust conduit 20 connected to a two-stage vacuum pump through a stop-cock 21. The pipe assembly shown on the right is connected to the atmosphere and to supplies for the requisite gases. A high-voltage direct-current source is connected between the cathode assembly 15 and the earthed plate 18 through the rectified circuit shown. Various applications of supports treated in the above manner are referred to.