Method of fabricating a semiconductor device having epitaxial layer

Abstract

There is provided a method of fabricating a semiconductor device, including the steps of forming an insulating film and an electrically conductive film on a silicon substrate, forming a first opening in the insulating film and a second opening in the electrically conductive film, the second opening having a smaller length than the first opening so that tunnel portions are formed in the insulating film below the electrically conductive film, and forming a Si,Ge,base epitaxial layer on the silicon substrate in the first opening of the insulating film, wherein a process gas for growing the Si,Ge,base epitaxial layer includes disilane, an etching gas includes chlorine, a ratio of the chlorine to the disilane is greater than {fraction (1/50)}, and a growth temperature is smaller than 640° C. In accordance with the method, it is possible to form a SiGe base epitaxial film having a greater thickness at opposite ends thereof than a thickness at the center thereof. Hence, even if the SiGe epitaxial film is formed to have a great thickness at opposite ends thereof for making electrical contact with the electrically conductive film, a central portion of the SiGe epitaxial layer acting as a base can have a small thickness. As a result, whereas a SiGe base epitaxial layer occupied about 80% of a thickness of an insulating film in a conventional semiconductor device, the SiGe base epitaxial layer formed in the above-mentioned method merely occupies about 60-3% of a thickness of the insulating film. Thus, the SiGe base epitaxial layer can be formed thinner, which ensures a higher operation rate of a bipolar transistor.