Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, comprising:

• successively laminating a buffer insulation film, an oxidation-resistant insulation film and a first conductor film containing an impurity of a second conductivity type on a semiconductor layer having a collector region of a first conductivity type;
• forming a first protective insulation film by a deposition method on the first conductor film;
• forming an opening portion exposing the oxidation-resistant insulation film by selectively etching the protective insulation film and the first conductor film, an emitter diffusion region being formed later blow said opening portion;
• forming a second protective insulation film to cover the surface of the first conductor film exposed at a side wall of the opening portion;
• etching the oxidation-resistant insulation film exposed at the bottom of the opening portion using the first and second protective insulation films as an etching mask so as to expose the buffer insulation film, a predetermined size of a bore being formed by side etching below the conductor film;
• etching the exposed buffer insulation film to expose a surface of the collector region of the semiconductor layer;
• burying in the bore a second conductor film capable of an insulation film formation by surface oxidation and also capable of an impurity diffusion;
• applying a heat treatment under an oxidative atmosphere to form a thermal oxide film covering the exposed surface of the collector region and the surface of the second conductor film buried in the bore and to diffuse the impurity of the second conductivity type contained in the first conductor film into the collector region through the second conductor film so as to form an outer base region of the second conductivity type;
• doping the collector region with an impurity of the second conductivity type through the opening portion so as to form an inner base region of the second conductivity type;
• removing the thermal oxide film covering the bottom surface of the opening portion by anisotropic etching to expose a surface of the inner base region;
• forming a poly-Si film containing an impurity of the first conductivity type on the entire surface of the structure;
• forming an emitter region of the first conductivity type by thermal diffusion using as a diffusion source the poly-Si film containing an impurity of the first conductivity type;
• successively laminating a buffer layer and an aluminum film on the poly-Si film, the buffer layer acting as a barrier to mutual diffusion of poly-Si and aluminum;
• and
• forming an emitter electrode in ohmic contact with the emitter region by selectively etching and patterning the poly-Si film, buffer layer and aluminum film;
• wherein laminating the aluminum film comprises sputtering at 470.degree. C. to 520.degree. C. under conditions in which the deposited aluminum is fluidized and fills a recess in the opening portion above the emitter region.