| 摘要 |
PURPOSE:To increase latch-up withstanding voltage while reducing the number of ions implanted, and to improve productivity by forming a reverse conduction type second well region in a first well region of the same conductive type as a substrate. CONSTITUTION:Phosphorus 21 is implanted to the surface of an N type semiconductor substrate 20 consisting of silicon as an impurity. Phosphorus is driven into the whole through heat treatment in an atmosphere composed of a mixed gas of nitrogen and oxygen, and an N-well as a first well region 22 is formed. A resist film 24, to which a window 23 is bored while corresponding to a P-well forming prearranged region, is shaped on the first well region 22. Boron 25 is implanted as an impurity while using the resist film 24 as a mask. Phosphorus and boron are driven into the whole through test treatment in the atmosphere composed of the mixed gas of nitrogen and oxygen, and a P-well as a second well region 26 is formed in the N-well.
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