GB1249812A - Improvements relating to semiconductor devices - Google Patents

Abstract

1,249,812. Semi-conductor devices. FERRANTI Ltd. 13 May, 1970 [29 May, 1969], No. 27138/69. Heading H1K. A transistor 10 formed in a Si wafer of N conductivity material comprises a N conductivity collector 11, a P conductivity base 12 adjacent a major surface 13, and a N conductivity emitter 14 extending to the surface; the base and emitter being formed by diffusion through a Si oxide mask 15. The collector, base, and emitter base junctions comprise depletion layers 16, 17, and the oxide mask also passivates the surface portions of the junctions. Annular and circular apertures 18, 19 for base and emitter contacts are etched through the oxide layer, and a gold collector electrode 20 is provided on opposite face 21. The oxide layer 15 tends to lower the resistivity of the surface of annular portion 22 of the collector, and to diminish the thickness of the surface portions of the collector-base junction depletion layer, but base contact 23 in aperture 18 is connected to a field electrode 24 on the oxide layer overlying the collector portions 22, which is maintained at a potential difference thereto, producing an electric field across the oxide layer and counteracting the reduction in thickness of the depletion layer. This increases the breakdown value of the collector-base junction. The base and emitter contacts 23, 25 in apertures 18, 19 and the field electrode 24 are formed by selectively etching an aluminium layer deposited on the apertured oxide layer 15, and the field electrode 24 is connected to base contact 23 by a narrow aluminium neck or a small diameter wire 26 spanning a minor part of the surface of the depletion layer of PN junction 16, to avoid instability thereof.