GB1177320A - Improvements in or relating to the Production of Planar Semiconductor Components - Google Patents

Abstract

1,177,320. Semi-conductor devices. SIEMENS A.G. 20 Dec., 1968 [21 Dec., 1967], No. 60546/68. Heading H1K. A boron-oxide glass layer, produced during the diffusion of boron into a silicon wafer by a planar process, is heat treated in a moist atmosphere at a temperature of 300‹ to 900‹ C. to make it easier to etch and the treated glass layer is then completely or partially etched away. The glass layer may be covered with an oxide layer to prevent out diffusion of boron during the heat treatment. A diode, Figs. 1 and 2 (not shown), is produced by oxidizing the surface of an N-type silicon wafer, etching a window and diffusing-in boron to produce a P-type region. The boronoxide glass layer which forms during the diffusion is covered with a silicon dioxide layer by pyrolysis of tetraethoxysilane and the wafer is then heated in a stream of moist nitrogen. The surface is photo-resist masked and etched with hydrofluoric acid buffered with ammonium fluoride to expose areas of the diffused region and the substrate. A metal is then deposited in the windows to form electrodes which may be alloyed to the wafer. A PNP planar transistor, Fig. 3 (not shown), is produced by forming an N-type base layer at the upper face of a P-type silicon wafer by diffusion, oxidizing the surface, forming a window, and diffusing-in boron to produce a P-type emitter region. A layer of silicon dioxide is deposited over the boron-oxide glass layer formed during the diffusion, and the wafer is heated in a moist atmosphere. The surface is photo-masked and etched to expose part of the base region into which phosphorus is diffused to produce an N+ type base contact region. The high temperature phosphorus diffusion step reduces the etchability of the glass layer so that a second heat treatment in a moist atmosphere is necessary before masking and etching away the oxide and glass over the emitter region. Metal contacts are deposited on the exposed areas of the emitter and base regions and the collector contact is applied to the lower face of the body. Argon or oxygen may be used instead of nitrogen in the moist atmosphere.