Antimony-phosphor buried layer for a MOs FET or like semiconductor device, and method of fabrication

摘要

A composite semiconductor device is disclosed which is a one-piece construction of a metal oxide semiconductor field effect transistor and a bipolar transistor. In order to lower the on-state resistance of the MOS FET without giving an adverse effect to the bipolar transistor, buried layers for the component transistors are formed first by introducing antimony into first and second selected parts (20a and 11a') of a p type semiconductor substrate (1). Phosphor, more diffusive than antimony, is then introduced approximately into the first selected part of the substrate. As an n type epitaxial layer (4) is subsequently grown on the substrate, there are formed for the MOS FET a buried layer (20) in which antimony is higher in concentration than phosphor, and a pair of additional buried layers (21a and 21b) in which phosphor is higher in concentration than antimony. A buried layer (11) for the bipolar transistor is completed simultaneously which includes the preformed second selected part (11a) of the substrate and part (11b) newly formed in the epitaxial layer and which contains antimony only.