MANUFACTURE OF SEMICONDUCTOR ELEMENT HAVING TRIPLE WELL

PROBLEM TO BE SOLVED: To simplify processes and obtain stable characteristics, by forming a triple well with two masks when a transistor of a memory element is formed, in the case of manufacturing a semiconductor element having a triple well. SOLUTION: An element isolating mask is formed on the upper part of a silicon substrate 1, and N-type impurities are ion-implanted in the substrate by using an N-well mask. The N-well mask is eliminated, a field oxide film 7 is formed in a thermally oxidizing process, the N-type impurities are diffused in the substrate, and an N-well 8 is formed. That is, a drive-in process for forming an N-well is not separately performed, bit the N-well is formed. After a P-well mask 18 is formed, P-type impurities are implanted in the substrate with different concentration and ion implantation energy, and a P-well and a triple well wherein a P-well is arranged in the N-well region are formed on the silicon substrate.