Process for making a lateral bipolar transistor in a standard CSAG process

摘要

A method of forming a lateral bipolar transistor in a semiconductor substrate of a second conductivity type by an MOS or CMOS process which includes growing a thin insulating layer over the substrate and diffusing a tank region of a first type of conductivity into the semiconductor substrate of a polarity opposite to that of the second conductivity type. A strip of polysilicon is deposited around a region between the emitter area and collector area on a face of the substrate over said oxide. Next an emitter region having the form of a band enclosing an undiffused central region within the polysilicon strip and a collector region located outside of the strip are diffused into the tank. The polysilicon prevents diffusion of implanted impurity into the tank region over which is superimposed the polysilicon. An electrically conducting layer is formed over the emitter and a portion of the polysilicon. By using a strip of polysilicon to limit diffusion of the emitter and collector regions and by forming the emitter contact over both the emitter and polysilicon it is possible to achieve a smaller emitter geometry than is otherwise possible.