Methods for forming high gain tunable bipolar transistors

A method for forming a bipolar transistor, comprising:

• forming, in a semiconductor substrate, an emitter region having a first emitter portion of a first emitter thickness and a second emitter portion of a second emitter thickness, located laterally outboard of the first emitter portion, wherein the second emitter thickness exceeds the first emitter thickness;
• forming, in the semiconductor substrate, a base region having portions of varying lateral base widths underlying the emitter region, wherein a lateral base width is a dimension perpendicular to an upper surface of the bipolar transistor;
• and
• forming, in the semiconductor substrate, a collector region having a portion underlying the base region.

A method for forming a bipolar transistor, comprising:

• forming, in a semiconductor substrate, an emitter region comprising a first emitter portion of a first thickness and a second emitter portion of a second thickness larger than the first thickness;
• forming, in the semiconductor substrate, a base region comprising a first base portion of a first base width and a first lateral extent, a second base portion of a second base width different than the first base width and having a second lateral extent, and a third base portion lying laterally between the first base portion and the second base portion and having a third base width and a third lateral extent wherein the third base width is larger than the first base width;
• and
• forming, in the semiconductor substrate, a collector region comprising a buried layer region underlying the base region and a second collector portion extending from the buried layer region to a collector contact region and a third collector region lying above the buried layer region and underlying the first base portion of the base region.