IE33405B1 - Semiconductor wafers sub-dividable into pellets and methods of fabricating same - Google Patents

Abstract

1293807 Semi-conductor device GENERAL ELECTRIC CO 24 Nov 1969 [9 Dec 1968] 57442/69 Heading H1K [Also in Division C7] A junction containing semi-conductor wafer is passivated by covering at least one of the surfaces with insulation to leave certain areas exposed, removing material from these areas to below a junction and electrophoretically depositing a passivating material, e.g. glass or plastics, into the grooves so formed. Typically a silicon wafer with several junctions is surface oxidized in steam, has registering grids cut in the oxide on opposite faces by etching through a photo-resist or wax mask and is then treated in an etchant to form intersecting sets of grooves extending through the junctions nearest to each face. The oxide overhanging the grooves may be left or removed by brushing or immersion in an ultrasonically agitated inert fluid. An oxide layer up to 500 Š thick is next formed on the groove walls preferably by treatment with an oxidizing agent such as hydrogen peroxide of strong nitric acid. This treatment improves adhesion of the glass electrophoretically deposited in the next step, in which a number or wafers are treated sequentially in an apparatus, operation of which is described in detail. If the oxide overhang was removed the glass increases in thickness towards the base of the grooves, while if it is left on the reverse is true. After firing to coalesce the glass particles electrodes are provided, either before or after sub-division, e.g. by scribing along the grooves, in apertures grit blasted or etched through the oxide. In the completed controlled rectifier shown in Fig. 8 in which the electrodes consist of superposed vapour deposited layers of chromium, nickel and silver, one electrode is soldered to heat sink 804. The wafer is then coated with resilient silicone rubber 814 and a rigid silicone casing 812 injection moulded around it. The invention is also described applied in PN, PIN, PNP and NPN structures with the grooves sometimes limited to one face. [GB1293807A]