. . . "Still further, referring to FIG. 5C, an oxide film 320 is formed on the surface of the n-type third silicon substrate 142 using a thermal oxidation process or the like, and then a p-type dopant, for example boron (B) with a dopant concentration of about 5???1016 cm???3, is doped from the side of the oxide film 320 into the third silicon substrate 142 in order to form a p-type region." .