| 摘要 |
A trench MOSFET (30) is formed in a structure which includes a P-type epitaxial layer (34) overlying an N+ substrate (32). An N-type dopant is implanted through the bottom of the trench (35) into the P-epitaxial layer to form a buried layer below the trench, and after a up-diffusion step a N drain-drift region (33) extends between the N+ substrate and the bottom of the trench. The result is a more controllable doping profile of the N-type dopant below the trench. The body region (34A) may also be formed by implanting P-type dopant into the epitaxial layer, in which case the background doping of the epitaxial layer may be either lightly doped P- or N-type. A MOSFET constructed in accordance with this invention can have a reduced threshold voltage and on-resistance and an increased punchthrough breakdown voltage. |
