Process for preparing semiconductor device having active base region implanted therein using walled emitter opening and the edge of dielectric isolation zone

Claim 1

In a method of preparing a semiconductor device having a walled emitter structure covering at least one side surface with a dielectric layer for separation of a plurality of said devices wherein a collector is formed in a substrate by doping through the use of one of thermal diffusion and implantation of ions and wherein a surface oxide layer covering said collector and said substrate is removed with a epitaxial layer being grown on said collector and whereby said layer for separating each of a plurality of said devices is formed by selective oxidation and wherein a collector wall is formed by implantation of phosphorus ions through a first resist mask having an opening for forming said collector wall, the improved method comprising the steps of: forming a base by implantation of ions with a second resist mask with an opening to obtain a base; forming an emitter area by implantation of ions with a third resist mask having an emitter-opening portion and a collector-opening portion; forming an active base just below said emitter by implantation of ions through said emitter-opening portion and an edge of said separating oxide layer through the use of a fourth resist mask which is an over-size mask.