| 摘要 |
PROBLEM TO BE SOLVED: To reduce man-hours in a production process by forming the same conductivity wells forming a plurality of MOS transistors on a silicon substrate with impurity of substantially the same concentration, and ion-implanting the reverse conductivity impurity to the impurity in the wafer in gate-through. SOLUTION: A field isolation region film 12 is formed on a silicon substrate 10, a protective through-oxide film is formed thereon for ion-implantation, and photoresists 13 for forming a 1.8 V n-well and a 3.3 V n-well are patterned. The patterned photoresists 13 are used as masks to implant phosphorus three times continuously under a specified condition, and As is then implanted under a specified condition to form an n-well 16 for a 1.8 V-pMOS and a well 17 for a 3.3 V-pMOS. Phosphorus is ion-implanted as impurity for each of wells 16 and 17 through As having the reverse conductivity in gate-through.
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