| 摘要 |
PURPOSE:To stabilize a Zener voltage without an additional diffusion process by a method wherein an N-type epitaxial layer is formed on a P-type semiconductor substrate and a P<+> type buried layer, P<+> type diffused regions, a P<+> type first region and an N<+> type second region, which has a larger aperture than the first region and is formed slightly overlapping the first region, are formed in the bottom part and the surface parts of the N-type epitaxial layer by the lower side separating diffusion and the upper side separating diffusion respectively. CONSTITUTION:An N-type epitaxial layer 3 which is formed on a P-type semiconductor substrate 1, a P<+> type buried layer 15 which is formed in the bottom part of the epitaxial layer 3 by the lower side separating diffusion, P<+> type diffused region 16 and 18 and a P<+> type first region 17 which are formed in the surface part of the epitaxial layer 3 so as to reach the buried layer 15 by the upper side separating diffusion and an N<+> type second region 19 which is formed by the upper side separating diffusion and has a larger aperture than the first region 17 and is formed slightly overlapping the first region 17 are provided. In an island region 5 obtained with this constitution, a Zener diode which has the second region 19 as a cathode and the first region 17 as an anode is formed. With this structure, a breakdown voltage is determined only by the second region 19 and the first region 17. Therefore, a variation of an impurity concentration is completely eliminated and a stable Zener voltage can be obtained.
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