PROCEDE DE FABRICATION D'UN CIRCUIT INTEGRE A SEMI-CONDUCTEUR

Method for fabricating a semiconductor integrated circuit structure. Improved control over the number of active base zone impurities, and therefore, over transistor gain, is achieved by ion implanting a buried base zone into an epitaxial layer formed on a substrate containing a collector, and then introducing impurities into the epitaxial layer portion substantially only above the buried base zone to form an emitter zone. Additionally, deep collector contact impurities are implanted through a silicon nitride mask into the epitaxial layer to improve control of series collector resistance. Heating in an oxidizing atmosphere diffuses the implanted collector contact impurities through the epitaxial layer to form a deep collector contact zone and oxidizes the zone's unmasked top surface to form a precisely aligned protective cap.