A semiconductor device including a transistor having an SOI structure the operating speed of which is not affected is provided. A MOS transistor having the SOI structure is formed which satisfies RCf<1 where C is a gate capacitance (F), R is a body resistance (.OMEGA.), f is a clock operating frequency (Hz), and f.gtoreq.500 MHz.
A semiconductor device including a SRAM section and a logic circuit section includes: a first n-type MIS transistor including a first n-type gate electrode formed with a first gate insulating film interposed on a first element formation region of a semiconductor substrate in the SRAM section; and a second n-type MIS transistor including a second n-type gate electrode formed with a second gate insulating film interposed on a second element formation region of the semiconductor substrate in the logic circuit section. A first impurity concentration of a first n-type impurity in the first n-type gate electrode is lower than a second impurity concentration of a second n-type impurity in the second n-type gate electrode.
Silicon-on-insulator (SOI) devices with reduced polysilicon loading on an active area uses at least one dielectric layer resistant to silicidation to separate at least one body contact region from source/drain regions, thus reducing gate capacitance and improving device performance. The SOI devices may be used in full depletion type transistors or partial depletion type transistors.
