Method for manufacturing a bicmos semiconductor device

Abstract

In a method for manufacturing a BiCMOS semiconductor device including bipolar transistors and MOS transistors, a thin gate oxide film is formed on a principal surface of a semiconductor substrate, and a first polysilicon film is formed on the thin gate oxide film. This first polysilicon film is selectively removed from a bipolar transistor formation area, and impurities are introduced into a principal surface region of a semiconductor substrate through only the thin gate oxide film so that a collector region is formed in the semiconductor substrate in the bipolar transistor formation area, and a base region is formed in the collector region, Therefore, a second polysilicon film is formed on the whole surface, and the second polysilicon film and the underlying thin gate oxide film are removed from an emitter formation area within the base region. A third polysilicon film having a high impurity concentration is formed on the whole surface, and thereafter, the polysilicon layers are patterned to form a gate composed of the first, second and third polysilicon films, and an emitter composed of the second and third polysilicon films. The impurity included in the third polysilicon is thermally diffused in the base region so that an emitter region is formed in the base region. Thus, without increasing the number of masks, and without giving an adverse influence to the MOS transistor, the performance of the bipolar transistor can be elevated, and the stable yield of production can be realized. In addition, the microminiaturization of the bipolar transistor becomes possible