| 摘要 |
PURPOSE:To achieve the formation of a graft base region having a submicron width by a method wherein, when a polycrystalline semiconductor layer is wet-etched by making use of a side wall as a mask, in undercut part is formed at the polycrystalline semiconductor layer located under the side wall. CONSTITUTION:After a polycrystalline Si layer 7 undoped with an impurity has been formed on the whole surface by a CVD method, an SiO2 layer doped with boron is formed on the surface of this layer by a CVD method. After that, by etching the whole surface by an RIE method, a side wall 9 of SiO2, acting as an etching mask layer, is formed on the side wall of recessed part 8 at the Si layer 7 formed by an opening 6. Then, the Si layer 7 is etched by KOH by making use of side wall 9 as a mask. The etching process is stopped on the substrate 1 due to the selectively of the KOH. In order to keep a distance from a P<+> type graft base region 13 and an N<+> type emitter region 15 which are to be formed later, an undercut part 10 is formed by overetching the Si layer 7.
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