Heterojunction bipolar transistor and method of making heterojunction bipolar transistor

Abstract

A method of making a heterojunction bipolar transistor comprises the steps of: forming a mask layer on a compound semiconductor film by using a photomask for forming an emitter; and forming the emitter by wet-etching the compound semiconductor film by using the mask layer. The photomask has a pattern thereon for forming the emitter. The pattern is defined by a first area R associated with the shape of the emitter to be formed, and a plurality of second areas T1 to T4. Each of the second areas T1 to T4 includes first and second sides S1 and S2 meeting each other to form an acute angle therebetween, and a third side S3 in contact with the first area R. In each of the second areas T1 to T4, one side S3 of the two sides meeting each other to form a right angle therebetween is in contact with one side of the area R, whereas the other side S1 is connected to another side of the first area R to form a line segment. Using this photomask, an etching mask is arranged such that a side S11 of the first area R is oriented in [001] direction of the emitter crystal film. When the emitter crystal film is etched by use of the etching mask, a rectangular emitter is obtained.

Dependencies are inferred from the claim text.