1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, for instance, which is used for a nonvolatile semiconductor memory.
2. Description of the Related Art
In some of the semiconductor integrated circuits, voltages (except for 0V) are used in one chip (referring to Jpn. Pat. Appln. KOKAI Publication No. 2003-37250).
For instance, in a flash memory, for high-speed operation, at the time of erasing, a voltage of not less than 15V and not more than 40V is applied to a well, while at the time of reading/writing, its well voltage is made zero. Further, a peripheral circuit for switching the voltage of the well is driven with a voltage of not less than 1V and not more than 5V applied for low power consumption.
For this reason, it becomes necessary for the flash memory to be provided with a high-voltage transistor in which the voltage of not less than 15V is applied to its gate, and a low-voltage transistor in which the voltage of not less than 1V and not more than 5V is applied to its gate.
However, when such plural transistors with plural voltages are formed in one chip, the manufacturing process is complicated; accordingly, problems of variations of a threshold voltage or deterioration of a short channel effect by the manufacturing process occur.