| 摘要 |
PURPOSE:To suppress a software error due to alpha-rays and to realize high integration by forming a well for forming a transistor to form an FF shallower than a well for forming a transfer gate and a peripheral circuit or in high impurity density. CONSTITUTION:A p-well 11 of an FF of a memory cell, a transfer gate,and a p-well 12 of a peripheral circuit are formed in an n-type Si substrate 1. The well 11 is formed in higher density and/or shallower than the well 12. N-channel transistors are formed in the wells 11, 12. When the well 11 is shallow, the alpha-ray passing distance in the well is shortened to suppress a software error due to the alpha-ray of the memory cell. The area of the memory cell can be reduced to raise the integration. If the well 12 is deep, it can suppress a latchup phenomenon due to a parasitic thyristor of P-N-P-N structure formed in the substrate. If the density of the well 11 is high, information is hardly inverted. When the well 12 is further low in density, its turning OFF operation is accelerated to accelerate the device. |
