Self-aligned Bi-CMOS device having high operation speed and high integration density

Claim 1

A process for manufacturing a semiconductor device which includes at least one bipolar transistor, one N-channel MOS transistor and one P-channel transistor which are formed in the same semiconductor substrate at the same semiconductor layer level, comprising: preparing a substrate including a bipolar transistor section including a collector region formed in said semiconductor substrate, and a first conduction type well for a first type MOS transistor and a second conduction type well for a second type MOS transistor, the bipolar transistor section, the first conduction type well and the second conduction type well being isolated from each other and covered by a first insulating layer formed on the principal surface of the semiconductor substrate; selectively etching said first insulating layer to expose a portion of said bipolar transistor section and forming a first polycrystalline semiconductor layer on said first insulating layer and said exposed portion of said bipolar transistor section; selectively doping a first impurity to a portion of said first polycrystalline semiconductor layer on said exposed portion of said bipolar transistor section and on said first conduction type well, respectively, and also selectively doping to a second impurity of a conduction type opposite to that of said first impurity, to another portion of said first polycrystalline semiconductor layer on said second conduction type well and on another portion of said bipolar transistor section, respectively; selectively removing a portion of said first polycrystalline semiconductor layer on said first conduction type well, said second conduction type well and on said another portion of said bipolar transistor section so as to partially expose said first insulating layer; forming a second insulating layer on said first polycrystalline semiconductor layer and a portion of said first insulating layer respectively exposed in said first conduction type well, said second conduction type well and said bipolar transistor section; over-etching said exposed portion of said first insulating layer by using said second insulating layer as a mask so that said first insulating layer under said first polycrystalline semiconductor layer is partially removed; filling a polycrystalline semiconductor to a space formed under said first polycrystalline semiconductor layer as the result of said over-etching and then selectively removing said filled polycrystalline semiconductor so as to leave said filled polycrystalline semiconductor under said first polycrystalline semiconductor layer; heating said substrate so that the impurities included in said first polycrystalline semiconductor layer are respectively diffused to said first conduction type well, said second conduction type well and said bipolar transistor section; selectively doping impurity to only a portion of said bipolar transistor section which is not covered by said first polycrystalline semiconductor layer so that a base region is formed; forming an oxide layer on said first conduction type well, said second conduction type well and said bipolar transistor section which are not covered by said first polycrystalline semiconductor layer so that said oxide layer formed on said first conduction type well and said second conduction type well forms a gate insulator; selectively removing only said oxide layer on said bipolar transistor section which is not covered by said first polycrystalline semiconductor layer so that an area within said base region where an emitter region is to be formed is exposed; depositing a second polycrystalline semiconductor layer including a predetermined conduction type of impurity, on said second insulating layer, said gate insualtor on each of said first conduction type well and said second conduction type well, and said emitter formation area in said bipolar transistor section; and heating said substrate to cause said predetermined conduction type of impurity contained in said second polycrystalline semiconductor layer to be diffused to said emitter formation area in said bipolar transistor section so that an emitter region is formed in said bipolar transistor section.