Patent GB-1147205-A (GB)
Title: Improvements in and relating to semiconductor devices
IPC: H01L23/29
Filed: 1966-06-02
Abstract: 1,147,205. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 2 June, 1966 [5 June, 1965], No. 24575/66. Heading H1K. In a semi-conductor arrangement, two surface regions of the same conductivity type and doping concentration and covered with oxide layers are given different electrical properties by providing the overlying oxide layers with different properties. The different electrical properties are achieved by forming the oxide on one of the regions so that it produces an inversion layer in the surface of the region. In a first embodiment, Fig. 1 (not shown), two identical insulated gate FET's are formed in a semi-conductor body by diffusing in the source and drain regions and applying a gate electrode over the insulating layer, the gate insulation of one of the transistors having been treated so that an inversion layer is formed between the source and drain. The untreated device operates in the enhancement mode with zero drain current at zero gate bias while the treated device has an appreciable drain current at zero gate voltage and so can be used in either the depletion or the enhancement mode. In a second embodiment, Fig. 3 (not shown), a bipolar transistor and an FET are manufactured by diffusing two regions into a wafer and then diffusing a region of the opposite type into one of the first regions to form the bipolar transistor and simultaneously diffusing two regions of the opposite type into the other of the first regions to form the source and drain of the FET. The oxide covering the channel of the FET is then treated to form an inversion layer. The invention may be applied to other combinations of semi-conductor devices in which an inversion layer is required over certain areas, the combination of a transistor and a thyristor being mentioned. The devices may be produced by polishing a P-type silicon wafer doped with indium, etching the surface and thermally oxidizing in moist oxygen. The oxide is photomasked and etched to form windows into which phosphorous is diffused by heating in nitrogen containing phosphorous pentoxide and then heating to drive-in the phosphorous. Methods of treating the silicon dioxide layer to produce selectively the inversion layer are described and include; locally removing the phosphorous-containing surface of the oxide layer, produced during the diffusion; locally depositing silicon monoxide, by evaporation in vacuo, on the silicon dioxide layer and heating in dry oxygen; irradiating with X-rays and U.V. radiation; replacing part of the oxide masking layer with an oxide layer produced by heating in oxygen saturated with steam; heating in hydrogen; locally depositing a metal (e.g. aluminium) on the oxide, heating, and then removing the metal; removing the oxide and selectively depositing different oxides such as silicon oxide and lead oxide or silicon oxide and aluminium oxide; applying a temperature gradient between the faces of the wafer; and heating locally using I.R. radiation. The invention may be applied to devices made from germanium and to bodies comprising layers of semi-conductor material on an insulating substrate.