TRENCH-GATE SEMICONDUCTOR DEVICES AND THEIR MANUFACTURE

摘要

In a trench-gate semiconductor device, for example a cellular power MOSFET, the gate (11) is present in a trench (20) that extends through the channel-accommodating region (15) of the device. An underlying body portion (16) that carries a high voltage in an off state of the device is present adjacent to a side wall of a lower part (20b) of the trench (20). Instead of being a single high-resistivity region, this body portion (16) comprises first regions (61) of a first conductivity type interposed with second regions (62) of the opposite second conductivity type. In the conducting state of the device, the first regions (61) provide parallel current paths through the thick body portion (16), from the conduction channel (12) in the channel-accommodating region (15). In an off-state of the device, the body portion (16) carries a depletion layer (50). The first region (61) of this body portion (16) is present between the second region (62) and the side wall (22) of the lower part (20b) of the trench (20) 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 (62). A balanced space charge is nonetheless obtained by depletion of the first and second regions (61, 62), because the width (W1) of the first region (61) is made smaller than the width (W2) of the lower-doped second region (62). 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 (20b) into the lower-doped second region (62) to form the first region (61).