| 摘要 |
PURPOSE:To minimize the number of increasing processed for forming transistors having different current amplification factors, by forming the base region of a transistor, thereafter selectively forming a thermal oxide film on said base region, and differentiating base widths. CONSTITUTION:An N-type epitaxial layer, which is formed on a P-type silicon substrate 1, is isolated into islands by P<+> type isolating diffused regions 3, and N-type epitaxial island regions 4 and 5 are formed. P<+> type base regions 6 and 7 are formed therein. Thereafter, only a silicon dioxide film on the P<+> type base region 7 is removed. Heat treatment is performed in an oxidizing atmosphere. Silicon in the surface of the P<+> type base region is also oxidized. Since the surface is covered with a thick oxide film before heat treatment, the amount is very small. The depths from the silicon surfaces in the P<+> base regions 6 and 7 are different. Namely, by the heat treatment in the oxidizing atmosphere, two kinds of transistors having the different current amplification factors can be formed on the single semiconductor substrate. |
