GB908846A - Method of passivating a silicon semiconductor surface - Google Patents

Abstract

908,846. Semi-conductor devices. PACIFIC SEMICONDUCTORS Inc. Oct. 27, 1960 [Jan. 4, 1960], No. 36995/60. Class 37. A silicon semi-conductor body is protected from moisture and undesirable impurities by forming an oxide layer on its surface and then treating the oxide layer with an esterifying agent. Particularly suitable esterifying agents suggested are methyl and ethyl alcohols, trimethylmethoxysilane, triethylethoxysilane, and trivinylethoxysilane but many others are mentioned. Diodes protected in this way are made by the following steps. Boron is first diffused into one surface of a 40 ohm. cm. N-type silicon wafer to form a junction therein. The diffused surface is masked, a grid of lines scribed through the masking, and the surface exposed to an etch until the lines extend through the junction to provide a series of discrete P-type mesas. After removal of the masking the wafer is heated at 1000‹ C. for 2 hours in oxygen at ¥ of an atmosphere pressure to produce a silicon dioxide film 1000-10,000 Š thick. After removal of the film from the upper and lower surfaces the wafer is broken up along the lines into separate PN elements to which gold-plated nickel ribbons 40, 41 (Fig. 6) are then welded. The elements are next placed on quartz wool 51 in tube 50 which is evacuated via tube 55. During this process the methylmethoxysilane is frozen in container 62 by liquid nitrogen 66. The liquid nitrogen is moved to surround base of tube 50 so that the silane distils over to form pool 70. The tube is then sealed off at 72, mounted in an autoclave containing the silane to equalize the internal and external pressures on the tube and heated to 250‹ C. for 16 hours, during which the pressure in the tube is 200- 350 p.s.i. The final protective layer 90 (Fig. 6) is subsequently formed by the method described in U.S.A. Specification 2,913,358. As an alternative the oxide film is formed by a process identical to that used in the esterification step except that deionized water is used in place of the silane. A theoretical explanation of the esterification process is given in terms of the reaction with hydroxyl ions of water atoms trapped on the surface.