Trench-gate semiconductor devices and their manufacture

Abstract

In a trench-gate semiconductor device, for example a cellular power MOSFET, the gate ( ) is present in a trench ( ) that extends through the channel-accommodating region ( ) of the device. An underlying body portion ( ) that carries a high voltage in an off state of the device is present adjacent to a side wall of a lower part ( ) of the trench ( ). Instead of being a single high-resistivity region, this body portion ( ) comprises first regions ( ) of a first conductivity type interposed with second regions ( ) of the opposite second conductivity type. In the conducting state of the device, the first regions ( ) provide parallel current paths through the thick body portion ( ), from the conduction channel ( ) in the channel-accommodating region ( ). In an off-state of the device, the body portion ( ) carries a depletion layer ( ). The first region ( ) of this body portion ( ) is present between the second region ( ) and the side wall ( ) of the lower part ( ) of the trench ( ) and has a doping concentration (Nd) of the first conductivity type that is higher than the doping concentration (Na) of the second conductivity type of the second region ( ). A balanced space charge is nonetheless obtained by depletion of the first and second regions ( ), because the width (W ) of the first region ( ) is made smaller than the width (W ) of the lower-doped second region ( ). This device structure can have a low on-resistance and high breakdown voltage, while also permitting its commercial manufacture using dopant out-diffusion from the lower trench part ( ) into the lower-doped second region ( ) to form the first region ( ).