Method of manufacturing MOSFET and structure thereof

A MOSFET, comprising:

• a substrate having a trench formed therein and a shallow trench isolation region enclosing the trench;
• an insulating layer at a bottom of the trench;
• a spacer on a side-wall of the trench;
• a doped semiconductive layer disposed over the trench and on the substrate, wherein the doped semiconductive layer partially covers the trench, and the shallow trench isolation region encloses the trench and the doped semiconductive layer;
• a gate dielectric layer comprising a first portion and a second portion, wherein the first portion is formed on and fully covers a top surface of the doped semiconductive layer and the second portion is formed on and partially covers a bottom surface of the doped semiconductive layer;
• a gate comprising a first portion formed on the first portion of the gate dielectric layer, so that the first portion of the gate is disposed above the trench, and a second portion formed on the second portion of the gate dielectric layer, so that the second portion of the gate is disposed in the trench, wherein the first and second portions of the gate formed on the first and second portions of the gate dielectric layer enclose a portion of the doped semiconductive layer that is over the trench;
• and
• a source/drain region in the substrate under the doped semiconductive layer and formed on either side of the gate by ion implantation or diffusion doping using the gate as a mask, wherein the shallow trench isolation region abuts the source/drain region.