High breakdown voltage semiconductor device

Claim 1

A semiconductor device having a semiconductor body comprising a surface-adjoining semiconductor layer of a first conductivity type which is situated on a substrate region of the second opposite conductivity type and forms a p-n junction therewith, a separation region which extends from the surface over substantially the whole thickness of the semiconductor layer and surrounds an island-shaped region of the semiconductor layer, within which island-shaped region are present an active zone of the second conductivity type belonging to a semiconductor circuit element and a juxtaposed contact zone of the first conductivity type having a higher doping concentration than the semiconductor layer, the active zone and the contact zone both adjoining the surface and at least the contact zone being further surrounded entirely by the island-shaped region, the thickness and the doping concentration of the island-shaped region being so small that upon applying a voltage in the reverse direction across the p-n junction, the depletion zone extends up to the surface at a voltage which is lower than the breakdown voltage of the p-n junction, characterized in that between the semiconductor layer and the substrate region a buried layer of the first conductivity type is present having a higher doping concentration than the semiconductor layer and extending at least below at least a portion of the said active zone and is separated from the active zone by the island-shaped region, in which, in projection, the distance in μm between the edge of the buried layer and the edge of the contact zone is at least equal to 2V.sub.B /E.sub.c wherein E c is the critical field strength in volts per μm above which avalanche multiplication occurs in the semi-conductor layer, and V B is the breakdown voltage in volts of the p-n junction.