Semiconductor device and method of manufacturing said device

Claim 1

A planar semiconductor device containing a thyristor, said device comprising a semiconductor substrate, a first epitaxial layer on the semiconductor substrate and a second epitaxial layer on the first epitaxial layer, said first and second epitaxial layers both being of a first conductivity type and the substrate being of a second conductivity type, a first buried layer of the first conductivity type and having a lower resistivity than that of the substrate and of both epitaxial layers and located at the interface between the substrate and the first epitaxial layer, a second buried layer of the second conductivity type and having a lower resistivity than that of both epitaxial layers and located at the interface of the first and second epitaxial layers, a first surface zone of the first conductivity type in the second epitaxial layer and over both buried layers, a second surface zone of the second conductivity type in the second epitaxial layer and fully surrounding the first zone and over both buried layers, a surface connection zone of the second conductivity type extending down to the second buried layer, said second zone being spaced from the second buried layer and its connection zone by a middle region of the first conductivity type of the material of the second epitaxial layer, a surface connection to the first zone and forming one of the thyristor cathode or anode, a surface connection to the second zone and forming the thyristor control electrode, and a surface connection via the connection zone to the second buried layer and forming the other of the thyristor cathode or anode, said first buried layer extending underneath and spaced from the second buried layer in order to reduce the gain of the parasitic transistor formed by the second buried layer, the first epitaxial layer and the substrate. CM,2Vice as set forth in claim 1 wherein isolation walls of the second conductivity type extend from the surface through both epitaxial layers to the substrate, said isolation walls being spaced from the second surface zone, and both buried layers