| 摘要 |
PROBLEM TO BE SOLVED: To reduce the difference in the level between the wells of a semiconductor element having a twin well structure, by forming a p-well region in the lower position than an n-well region, and performing the compensation of difference in the level caused by the capacitor made in a p-well region, in advance. SOLUTION: Exposed silicon is oxidized by performing a heat treatment, and an insolation film 116, 5000Åthick is grown in a field region, and a section A becomes the structure of element isolation by a silicon field (buffered). Since the n-well region 110 in the peripheral circuit region is made higher by a difference d" in level than the p-well region 112 in the cell region, the difference in the level caused by the capacitor in the cell region can be compensated in advance as the structure of the well. Formation process of a well in condition that the element isolation is completed, with a silicon nitride film 114, a thermal oxide film 102, and a polysilicon film 104 removed, is finished, Hereby, the low step difference problem of the n-well lying in a DRAM cell can be solved.
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