Trench-gate semiconductor devices

Abstract

A trench-gate MOSFET or ACCUFET has its gate ( ) in a first trench ( ) that extends through a channel-accommodating body region ( ) to a drain region ( ). Within the transistor cells, a second trench ( ) comprising deposited highly-doped semiconductor material ( ) extends to the drain region ( ). This highly-doped material ( ) is of opposite conductivity type to the drain region ( ) and, together with a possible out-diffusion profile ( ), forms a localized region ( ) that is separated from the first trench ( ) by the body region A source electrode ( ) contacts the source region ( ) and the whole top area of the localized region ( ). In a MOSFET, the localized region ( ) provides protection against turning on of the cell's parasitic bipolar transistor. In an ACCUFET (FIG. ), the localized region ( ) depletes the channel-accommodating body region ( A). In both devices the localized region ( ) is well-defined and can be narrow to enable a small transistor cell size. Furthermore, before filling the second trench ( ) with its semiconductor material ( ), the drain region ( ) can be readily provided with an avalanche-breakdown region ( ) at the bottom of the second trench ( ), for example by implanting dopant ions ( ) of the same conductivity type as the drain region ( ). This avalanche-breakdown region ( ) improves the ruggedness of the device. It can also aid current spreading ( ) in the drain region ( ) in the conductive state of the transistor.