INSULATED GATE SEMICONDUCTOR DEVICE AND ITS MANUFACTURING METHOD

PROBLEM TO BE SOLVED: To solve a problem in the conventional case wherein a gate oxide film in a channel region is thinned in a power MOSFET of a trench type so that a gate oxide film in a bottom part of a trench is also thinned, and large feedback capacitance is caused between a gate and a drain which capacitance becomes a large factor of deteriorating switching speed and performance of a transistor in the power MOSFET. SOLUTION: A thick oxide film is formed in the bottom part of the trench while the gate oxide film in the channel region is thin as it is, so that a merit that feedback capacitance can be made almost one-third the conventional case is obtained. As a result, a merit that switching speed of the trench type power MOSFET is improved and performance of a transistor is remarkably improved is obtained.