GB814527A - Improvements in or relating to processes for the production of electrodes on semi-conductor surfaces, and semi-conductor arrangements produced by such processes - Google Patents

Abstract

814,527. Semi-conductor devices. SIEMENS & HALSKE A.G. June 23, 1955 [Sept. 15, 1954 (2); June 23, 1954; Dec. 17, 1954], No. 18196/55. Drawings to Specification. Class 37. An electrode is provided on a semi-conductor body by first chemically etching part of the surface of the body, providing a pure homogeneous foreign layer on that part by oxidisation of the body or deposition of a semi-conductor layer and then depositing a metallic layer by an electrolytic or chemical process. The erosion may be effected by means of an anhydrous flux at a raised temperature. The metal layer may consist of an alloy or compound of two metals which may be used to promote deposition or to influence the impurity centre characteristics in the semi-conductor, which may be effected by heat treatment after the metallizing process is completed. The erosion and the metallizing processes may be assisted by employing ultrasonic vibrations. In one example, the opposite surfaces of a silicon crystal which is intended to serve as a transistor are treated with hot caustic soda and then irradiated with ultra-violet light in oxygen to produce an oxide layer. Potassium - copper cyanide (K 3 CuCN 4 ) is applied so that thin layers of copper are provided by ion exchange which is thickened electrolytically. In a second example the surface of a silicon crystal is treated with a mixture of 40 per cent hydrofluoric acid and fuming nitric acid, irradiated with X-rays in air and then dipped into a flux of alkali halide and electrolytically coated with aluminium, indium or gallium. In an alternative arrangement, a very thin (<SP>1</SP>/ 100 Á, or a few molecules) P-type or insulating layer is provided between the N-type semi-conductor body and the metallizing, by subjecting the surface to a liquid or gaseous medium, or irradiation by ultra-violet or X-rays, in an oxygen atmosphere. The additional layer may consist of titanium dioxide, or a mixture of oxides or chalcogenides, and may be of N-type material if associated with a P-type semi-conductor. The layer should be thick enough to be coherent but thin enough to allow charge carriers to penetrate it. The metallized electrode may consist of gold, silver or copper. The eroding agents and associated materials should be of extremely high purity and pure caustic soda for use with silicon may be prepared by lengthy electrolysis with pure silicon electrodes. The semi-conductor material may consist of silicon, germanium, compounds of elements of the 3rd and 5th, or of the 2nd and 6th groups of the Periodic Table, or multiple compounds or alloys thereof. Specification 694,021 is referred to.