| 摘要 |
PURPOSE:To form MOS transistors in different operational characteristics by a method wherein a dual well structure formed of a well in the same conductivity as that of a substrate in the other well in the inverse conductivity to the former conductivity formed on the semiconductor substrate is used. CONSTITUTION:Firstly, a P well 2 is formed on an N type substrate, then a P well 2 is overlapped with an N well 31 to form N wells 3, 31. These wells can be simultaneously formed by ion implantation process. At this time, the N type substrate 1 and the N well 31 can be electrically isolated from each other by forming the N well 31 shallower than the P well 2 to be enclosed by the P well 2. For example, assuming a voltage V3 to be fed to the P well 2 as the ground potential, the N type substrate 1 and the N well 31 can be impressed with different voltages e.g., V1 and V2 respectively. At this time, the impressed voltage on the N type substrate 1, the N well 31 and P well 2 shall be set up as the voltages not to be impressed on as a PN junction diode. |
