Vertical semiconductor device and method of manufacturing the same

DETAILED DESCRIPTION In the light of the above problems, it is an object of the present invention to provide an accumulation type field-effect transistor which has a high withstand voltage and suffers from a reduced leakage current.
The above object may be accomplished according to the principle of the present invention, which provides a vertical semiconductor device comprising: a semiconductor laminar structure including a semiconductor substrate of a first conductive type having a first impurity concentration, a first semiconductor layer of the first conductive type laminated on the semiconductor substrate and having a second impurity concentration lower than the first impurity concentration, and a second semiconductor layer of the first conductive type laminated on the first semiconductor layer and having a third impurity concentration lower than the second impurity concentration, the semiconductor laminar structure having a trench extending from a surface thereof through the second semiconductor layer to reach the first semiconductor layer; a source region of the first conductive type formed in a surface layer of the second semiconductor layer and having a fourth impurity concentration higher than the third impurity concentration; a gate electrode filling the trench through a gate oxide film; an insulating film formed on the gate electrode; a source electrode formed on a surface of the source region of the first conductive type; and a drain electrode formed on a rear surface of the semiconductor substrate of the first conductive type.
In the semiconductor device constructed as described above according to the present invention, the trench extends from the surface of the semiconductor laminar structure into the first semiconductor layer through the second semiconductor layer.
In this arrangement, the first semiconductor layer carries a part of the voltage applied between the source and drain electrodes, thereby reducing a voltage to be carried by the gate oxide film.
This eventually leads to an improved withstand voltage of the device