Self-aligned bipolar transistor with very thin dielectric layer interfacing between poly and active area

A bipolar transistor structure, comprising:

• a semiconductor substrate having an active area;
• a doped emitter having outer edges and a doped collector in said active area;
• a doped intrinsic base below said emitter;
• a doped extrinsic base lateral to said intrinsic base;
• an emitter contact contacting a portion of the upper surface of said emitter that is spaced inward from the emitter's outer edges;
• dielectric walls extending upward from said emitter lateral to said emitter contact, said dielectric walls having outer surfaces vertically aligned with the emitter's outer edges;
• a doped contact layer over said extrinsic base, said doped contact layer extending to said dielectric walls on either side of the emitter and having inner edges vertically aligned with the emitter's outer edges;
• a thin dielectric film about 10-20 Angstroms thick between said extrinsic base and said contact layer, said dielectric film extending to said dielectric walls on either side of the emitter and having inner edges vertically aligned with the emitter's outer edges;
• and
• collector and extrinsic base contacts.