PURPOSE: To prevent contamination, external diffusion during thermal diffusion and lower the generation rate of crystal defect by leaving a thin thermal oxide film on the region where the P well may be formed.
CONSTITUTION: An N type Si substrate 11 is oxidized under the moistened condition in order to form an SiO2 film, a resist mask 13 is coated and ions are implanted. Thereafter, a P well 14 is formed under the SiO2 film 12. Next, the SiO2 film 12 is etched until the film thickness becomes about 500°C and the mask 13 is removed. The P well 14 is thermally diffused for about 15hr in the dried O2+N2 ambient at 1,200°C and then for about 15hr in the dried N2 ambient at 1,200°C. Thus, the P well 15 is completed. At this time, the region where the P well may be formed is also oxidized, forming a step between this region and P channel region. This step can be used as the alignment standard of the next photo-etching process. According to this structure, generation rate of crystal defect in the well region is lowered and yield and reliability of product can be improved.
KONDOU TAKEO
SAITOU YASUYUKI
KOBAYASHI KIYOSHI
ADACHI NOBUHIRO
