Bicmos process with low base recombination current bipolar transistors

Abstract

A process for manufacturing both field effect and bipolar transistors provides, in one embodiment, a polycide film over the gate and field oxides on the surface of the semiconductor substrate is patterned such that a protective structure of gate material is formed on top the base region of the bipolar transistor while the gate of the FET is formed. The channel region of the FET is defined by the gate, which also serves as a mask for etching away the gate oxide from the source and drain regions. The protective structure of gate material in the active region of the bipolar transistor is removed just before implantation to form the base of the bipolar transistor. In a second embodiment a silicon nitride oxidation mask for formation of filed oxide regions over the bipolar transistor and the FET active regions is formed and portions of the nitride oxidation mask is removed only from the FET active regions after field oxide regions are formed. The portion of the nitride oxidation mask is left intact through formation of the gate regions of the FET, formation of the oxide spacers of the FET active regions, and the formation of source and drain regions. The nitride oxidation mask over the bipolar active region is removed prior to the base implant step. With the nitride oxidation mask over the bipolar transistor active region, a VT implant into the FET active region is performed.