Method of fabricating a high-frequency bipolar transistor

Abstract

A bipolar transistor with improved high-frequency performance is invented. The improvement is attained by eliminating a parasitic base-collector capacitance. The invented transistor is constructed upon a semi-insulating substrate, and wherein a region which underlies an extrinsic base region is semi-insulative such that the extrinsic base region does not substantially overlap the collector contact region and the collector region when viewed in the direction perpendicular to the substrate. Here, it's worthwhile to point out that a portion under the extrinsic base region is made completely semi-insulative down to the substrate. As a result, the transistor has substantially no parasitic base-collector capacitance. Also, a novel method, utilizing a self-align technique which uses a 'first mask' for defining a collector contact region and a collector region, a 'second mask' for defining an extrinsic base region, and a 'third mask' determined by self-alignment using the first and the second mask for defining an emitter region, is disclosed to fabricate the bipolar transistor mentioned above.