| 摘要 |
PROBLEM TO BE SOLVED: To reduce dispersion of threshold voltage by forming an element isolating film on a well region, and then, removing the element isolating region having the second level of threshold voltage, and forming a transistor. SOLUTION: After formation of a well region 1 on a substrate, an element isolating region 2 is made, and an element isolating region 7 to form a transistor having a second level of threshold voltage. Then, a gate oxide film 5, a gate electrode 4, and a source and drain region 3 are formed, thus two kinds of transistors having a difference in threshold voltage are made. A necessity of taking the dispersion of the implanted impurity ions by an ion implanter and the dispersion of quantity of implanted impurity ions to a well region caused by the dispersion of gate oxide films into consideration vanishes for a transistor where impurity ions are to be implanted into the well region after formation of the gate oxide film. As a result, the dispersion of threshold can be reduced.
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