Trench MOSFET and method for fabricating the same

1. A method for fabricating a trench MOSFET, comprising:

providing a substrate having a body of a first conductivity type and an epitaxy layer of said first conductivity type on said body;

forming a trench by etching said epitaxy layer;

depositing a first insulating layer and a first polysilicon layer successively on said epitaxy layer, said first polysilicon layer filling said trench;

forming a first gate in said trench by etching said first polysilicon layer;

etching off an exposed portion of said first insulating layer, and depositing a second insulating layer and a second polysilicon layer successively, said second polysilicon layer filling said trench;

forming a second gate in said trench by etching said second polysilicon layer;

forming a well of a second conductivity type by performing a first ion implanting after etching off an exposed portion of said second insulting layer to expose said epitaxy layer;

forming a source region of said first conductivity type by performing a second ion implanting at said surface of said well;

depositing a third insulating layer on said source region and over said trench;

forming a gate opening and a source opening by etching, said gate opening extending through said third insulating layer, said second gate, said second insulating layer and into said first gate, and said source opening extending through said third insulating layer, said source region and into said well; and

forming metal plugs by filling a metal layer in said gate opening and in said source opening, respectively.

2. The method according to claim 1 , further comprising forming a gate metal and a source metal by extending said metal plugs above said third insulating layer when said metal plugs are formed.

3. The method according to claim 2 , further comprising depositing a drain metal on a back surface of said body after forming said gate metal and said source metal.

4. The method according to claim 3 , wherein said third insulating layer is an oxide layer.

5. The method according to claim 4 , wherein said metal plugs, said gate metal, said source metal and said drain metal are each made of aluminum alloy or copper, and are lined with a barrier metal stack of Ti/TiN, Co/TiN or Ta/TiN.

6. The method according to claim 1 , wherein said epitaxy layer has a doping concentration smaller than that of said body.

7. The method according to claim 1 , further comprising:

depositing a hard mask layer on said epitaxy layer before forming said trench; and

forming an etching opening by etching said hard mask layer.

8. The method according to claim 7 , wherein said hard mask layer is an oxide layer having a thickness of about 0.1 micrometer to about 1 micrometer.

9. The method according to claim 8 , wherein said etching opening has a width of about 0.5 micrometer to about 5 micrometers.

10. The method according to claim 1 , wherein said trench has a depth of about 0.5 micrometer to about 50 micrometers.

11. The method according to claim 1 , wherein said first insulating layer is an oxide layer having a thickness of about 0.1 micrometer to about 2 micrometers.

12. The method according to claim 11 , wherein a sum of a thickness of said first polysilicon layer and a thickness of said first insulating layer is larger than one half of a width of said trench.

13. The method according to claim 12 , wherein an upper surface of said first gate is about 0.1 micrometer to about 1 micrometer below an upper surface of said epitaxy layer.

14. The method according to claim 1 , wherein said second insulating layer has a thickness smaller than that of said first insulating layer.

15. The method according to claim 14 , wherein said second insulating layer is a gate oxide layer.

16. The method according to claim 15 , wherein an upper surface of said second gate is about 0 micrometer to about 0.1 micrometer below an upper surface of said epitaxy layer.

17. A trench MOSFET fabricated by said method according to claim 1 comprising:

a substrate having a body of a first conductivity type and an epitaxy layer of said first conductivity type on said body;

a trench extending into said epitaxy layer from an upper surface of said epitaxy layer;

a first insulating layer at a lower portion of an inner surface of said trench;

a first gate in said trench and having a lower portion surrounded by said first insulating layer;

a second insulating layer at an upper portion of said inner surface of said trench and covering said first gate, said first insulating layer and said second insulating layer together surrounding said first gate;

a second gate at an upper portion of said trench and surrounded by said second insulating layer, said second gate having an upper surface below an upper surface of said epitaxy layer;

a well of said second conductivity type at a surface portion of said epitaxy layer at both sides of said trench;

a source region of said first conductivity type at a surface portion of said well at both sides of said trench;

a third insulating layer at the top surface of said source region and over said trench;

a gate opening extending through said third insulating layer, said second gate, said second insulating layer and into said first gate;

a source opening extending through said third insulating layer, said source region and into said first gate; and

metal plugs in said gate opening and in said source opening, respectively.