Method of producing a metal-oxide semiconductor device

Claim 1

In a method for producing a metal-oxide semiconductor device comprising a semiconductor substrate of a first conductivity type with high-impurity density, which substrate functions as a drain layer, a transistor element disposed on a surface of the substrate, which transistor element comprises a low-impurity density region of the first conductivity type having a lifetime-reducing agent diffused therein, a base region of a second conductivity type embedded within the low-impurity density region of the first conductivity type and extending to a first surface of the transistor element, a high-impurity density region of the second conductivity type embedded within the base region and extending to the first surface of the transistor element, and a source region of the first conductivity type with high-impurity density embedded at the interface between the base region and the high-impurity density region of the second conductivity type, which source region extends to the first surface of the transistor element, whereby the first surface of the transistor element has the high-impurity density region, which is surrounded by the source region, which source region is in turn surrounded by the base region, which region is surrounded by the low-resistance layer, and a second surface of the transistor element, which surface is disposed toward the substrate, is the high-resistance material, and a gate electrode disposed over a gate-insulating film, which is in turn disposed over all of the base region and the low-resistance material portion of the first surface of the transistor element but not over the high-impurity density region of the second conductivity type, the improvement comprising of forming the low-impurity density region of the first conductivity type as two sub-layers, a first sub-layer disposed proximately to the substrate having high resistance and a second sub-layer with a resistance about one half the resistance of the first sub-layer, the two sub-layers together forming a single region of low-impurity density prior to diffusion of the lifetime-reducing agent.