Patent ID: 6703292
Filing Date: 2004-03-09
Classification: H01L

Abstract:
A method of fabricating a semiconductor wafer of a depletable multiple-region semiconductor material in the form of alternating p-type and n-type regions which together provide a voltage-sustaining space-charge zone when depleted, the method including the steps of:(a) providing a p-type silicon body having an acceptor doping concentration extending through the thickness of the body between opposite major surfaces of the body, which acceptor doping concentration corresponds to that required for the p-type regions of the material, (b) providing a neutron-absorbing mask over one of the major surfaces to mask areas of the silicon body where the p-type regions are to be left, the mask having window areas where the n-type regions are desired, the window areas alternating with the masking areas; (c) subjecting the silicon body to irradiation with collimated beams of thermal neutrons at the window areas in the mask so as to form the donor dopant concentration for the n-type regions by transmutation of silicon atoms into phosphorus, which donor dopant concentration extends across the thickness of the body between the opposite major surfaces of the body so that p-n junctions formed between the alternating p-type and n-type regions terminate at the opposite major surfaces of the body; and (d) wherein the neutron irradiation is continued until the resulting n-type regions with a width w2 have a donor dopant concentration Nd that is correspondingly higher than the acceptor doping concentration Na to satisfy, to within Â±10%, a net charge balance relationship Na.w1=Nd.w2 between the alternating p-type and n-type regions, where w1 is the width of the p-type regions, and the width w2 is less than the width w1.