Complementary npn/pnp structure for monolithic integrated circuits

Claim 1

A semiconductor structure comprising a layer of semiconductor material of one conductivity type and having a principal surface, the layer divided into a plurality of semiconductor areas electrically isolated from each other; a layer of protective material overlying selected portions of the principal surface; a vertical, double-diffused, NPN transistor located in one of the semiconductor areas, a vertical PNP transistor having a first region of opposite conductivity type located in another of the semiconductor areas, the region forming a first PN junction with the layer, the junction extending to have an edge at the principal surface; an epitaxial layer of semiconductor material of one conductivity type located along a portion of the principal surface over an exposed portion of the first region, the impurity concentration of the epitaxial layer away from the principal surface being less than 1016 dopant atoms per cubic centimeter; a second protective layer overlying selected portions of the epitaxial layer; a layer of conductive metal overlying portions of the second protective layer and extending therethrough to an exposed portion of the epitaxial layer where the impurity concentration is less than 1016 dopant atoms per cubic centimeter, the metal layer alloyed to the epitaxial layer to form a Schottky-barrier collector-base junction; a second region of one conductivity type located within the first region and interposed between the first region and the epitaxial layer, the second region forming a second PN junction with the first region that extends to have an edge at the principal surface, the second region having a relatively high impurity concentration, the epitaxial layer having a relatively low impurity concentration.