| 摘要 |
Multiple kinds of transistors exhibiting desired characteristics are manufactured in fewer process steps. A semiconductor device includes an element 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 isolation film of a first thickness, source/drain regions of second conductivity type and a gate electrode, and a second transistor formed in the second well and having a gate isolation film of a second thickness less than the first thickness, source/drain regions of the second conductivity type and a gate electrode. The first well has a first impunity concentration distribution which shows a maximum value only at the depth equal to or greater than the first depth. The second well has a second impurity concentration distribution which shows a maximum value also at the second depth. The second impurity concentration distribution is superposition of an impurity concentration distribution which shows a maximum value at a second depth less than the first depth on the first impurity concentration distribution.
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