| 摘要 |
PURPOSE:To dispense with a mask-alignment margin and to form finely an element by a method wherein an oxide film is formed on a prescribed region of a first base, an impurity under this oxide film is surrounded with a base region, the concentration of the impurity in the base region is reduced, a second base is formed and the first and second bases, whose impurity concentrations are different from each other, are formed by self alignment. CONSTITUTION:The bottom of an opening part 7a is oxidized and an oxide film 8 is formed. Impurities existing under the lower part of the film 8 in a p<+> base region 6 are taken in this film 8 and the concentration of the impurity in this region is reduced and a p<-> base 6b is formed. As a result, a p<+> base 6a and the p<-> base 6b are formed by self alignment. After that, the film 8 is removed by wet etching and an emitter polysilicon electrode 9 is formed on the surface. Arsenic ions, for example, are implanted and diffused in this electrode 9 as impurity ions and an emitter layer 10 is formed. Thereby, an N-P-N bipolar transistor is formed.
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