Trench-gate field-effect transistors with low gate-drain capacitance and their manufacture

Abstract

Trench-gate field-effect transistors, for example power MOSFETs, are disclosed having trenched electrode configurations ( ) that permit fast switching of the transistor, while also providing over-voltage protection for the gate dielectric ( ) and facilitating manufacture. The gate electrode ( ) comprising a semiconductor material of one conductivity type (n) is present in an upper part of a deeper insulated trench ( ) that extends into a drain region ( ) of the transistor. A lower electrode ( ) connected to a source ( ) of the transistor is present in the lower part of the trench. This lower electrode ( ) comprises a semiconductor material of opposite conductivity type (p) that adjoins the semiconductor material of the gate electrode ( ) to form a p-n junction ( ) between the gate electrode ( ) and the lower electrode ( ). The p-n junction ( ) provides a protection diode (D) between the gate electrode ( ) and the source ( ). The gate electrode ( ) is shielded from most of the drain region by the lower electrode ( ), so reducing the gate-drain capacitance and improving the switching speed of the transistor.