| 摘要 |
PURPOSE:To keep high frequency characteristic excellent by preventing oxidization of a gate electrode made of Mo which is apt to be oxidized during protective film formation period. CONSTITUTION:An Mo gate 3 is formed on a p-type Si substrate 1 to have a gate oxide film 2 between them. Formation of n<+>-type source and drain layers 4, 5 is done by diffusing impurity with this gate 3 utilized as a mask. Next thereto a polycrystalline Si film 6 which is formed without diffusion of impurity is fabricated on the surface of the Mo gate, and PSG7 is formed to cover them inclusively on the gate. PSG7 is perforated and Al wiring layers 8, 9 are provided. This constitution makes the Mo gate free from oxidization due to contact with the PSG since it is covered with polycrystalline Si film, and resistivity of it is kept unchanged. And in addition the polycrystalline Si layer does not work as a gate since it has no impurity, and input capacitance does not increase, and thus high frequency characteristic is kept unchanged. And threshold voltage is kept unchanged since P diffusion to the poly-Si layer from PSG is kept to be very small. |
