Semiconductor device

1. A trench MOSFET comprising:

an epitaxial layer;

a body region on the epitaxial layer, the body region and the epitaxial layer forming a first interface;

a trench;

a trench bottom oxide in the trench; and

polysilicon in the trench, the trench bottom oxide and the polysilicon forming a second interface;

wherein the first and second interfaces are substantially aligned or are at substantially the same level, such that an overlap between the body region and the trench bottom oxide is less than about 25 nm;

wherein a surface of the trench bottom oxide which is in contact with polysilicon is convex;

wherein the trench bottom oxide comprises a first trench bottom oxide portion occupying substantially the entire width of the trench, and a second trench bottom oxide portion directly on the first trench bottom oxide portion, the second trench bottom oxide portion occupying substantially less than the entire width of the trench;

wherein the second trench bottom oxide portion occupies a central portion of the trench with respect to the width of the trench; and

wherein the second trench bottom oxide portion extends to the top of the trench.

2. A trench MOSFET according to claim 1 , wherein a laterally outer region of the second interface is at substantially the same level as a region of the first interface.

3. A trench MOSFET according to claim 1 , wherein a region of the second interface which is immediately adjacent a sidewall of the trench is at substantially the same level as a region of the first interface.

4. A trench MOSFET according to claim 1 , wherein the highest point of the second interface is at substantially the same level as a region of the first interface.

5. A trench MOSFET according to claim 1 , wherein there is no overlap between the body region and the trench bottom oxide.

6. A trench MOSFET according to claim 1 , wherein the distance between the body region and the trench bottom oxide along a line defined by the trench side wall is less than about 0.2 μm.

7. A trench MOSFET according to claim 1 , wherein the overlap is an overlap between the body region and the trench bottom oxide along a line defined by the trench side wall.

8. A method of manufacturing a semiconductor device comprising:

forming a first trench bottom oxide portion occupying substantially the entire width of a trench;

forming at least one spacer in the trench and on the first trench bottom oxide portion; and thereafter

forming a second trench bottom oxide portion on the first trench bottom oxide portion, the second trench bottom oxide portion occupying:

substantially less than the entire width of the trench,

a central portion of the trench with respect to the width of the trench,

and extending to the top of the trench; and

using the at least one spacer so as to form the second trench bottom oxide portion in a self-aligned manner.

9. The method according to claim 8 , further comprising:

introducing a conductive material into the trench to form an electrical connection for connecting to a gate electrode;

forming a lightly-doped body region with an implanting process;

forming a highly-doped source region with the opposite type of implant species to that of the body region;

covering the gate electrode with a dielectric layer and depositing a metal layer being in electrical contact with the source region.

10. A trench MOSFET comprising:

an epitaxial layer;

a body region on the epitaxial layer, the body region and the epitaxial layer forming a first interface;

a trench;

a trench bottom oxide in the trench; and

polysilicon in the trench, the trench bottom oxide and the polysilicon forming a second interface;

wherein there is no overlap between the body region and the trench bottom oxide, and the distance between the body region and the trench bottom oxide along a line defined by the trench side wall is less than about 0.2 μm;

wherein a surface of the trench bottom oxide which is in contact with polysilicon is convex;

wherein the trench bottom oxide comprises a first trench bottom oxide portion occupying substantially the entire width of the trench, and a second trench bottom oxide portion directly on the first trench bottom oxide portion, the second trench bottom oxide portion occupying substantially less than the entire width of the trench;

wherein the second trench bottom oxide portion occupies a central portion of the trench with respect to the width of the trench; and

wherein the second trench bottom oxide portion extends to the top of the trench.