| 摘要 |
Multiple kinds of transistors exhibiting desired characteristics are manufactured in fewer processes. A semiconductor device includes an isolation region reaching a first depth, first and second wells of first conductivity type, a first transistor formed in the first well and having a gate insulating film of a first thickness, and a second transistor formed in the second well and having a gate insulating film of a second thickness less than the first thickness. The first well has a first impurity concentration distribution having an extremum maximum value only at the depth equal to or greater than the first depth. The second well has a second impurity concentration distribution which is superposition of the first impurity concentration distribution, and another impurity concentration distribution which shows an extremum maximum value at a second depth less than the first depth, the superposition shows also an extremum maximum value at the second depth.
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