Method of forming a high voltage device

1. A method of forming a device comprising:

providing a substrate prepared with an active device region, wherein the active device region includes gate stack layers of a gate stack comprising at least a gate electrode layer over a gate dielectric layer;

forming an implant mask on the substrate with a mask opening exposing a portion of a top of the gate stack, the mask opening having first and second opposing edges;

implanting ions through the mask opening and gate stack layers into the substrate to form a channel well in the substrate, wherein a first channel edge of the channel well extends beyond the first mask opening edge, wherein a first portion of the channel well is between the first channel edge and the first mask opening edge, the first portion defines a channel with a length L of a device; and

wherein the channel of the device is disposed under a mask portion and a second portion of the channel well is disposed below the mask opening.

2. The method of claim 1 wherein a top layer of the gate stack layers comprises the gate electrode layer.

3. The method of claim 2 wherein the gate electrode layer comprises silicon, including amorphous or polysilicon.

4. The method of claim 2 comprises:

patterning the gate stack layers to form a first gate edge of the gate stack; and

further comprises patterning the gate stack layers to form a second gate edge of the gate stack after forming the first gate edge.

5. The method of claim 4 wherein the first gate edge corresponds to a source edge of the gate of the device and the second gate edge corresponds to the drain edge of the gate of the device.

6. The method of claim 1 further comprises patterning the gate stack to at least remove a portion of the gate electrode layer after forming a first gate edge of the gate to form a second gate edge of the gate.

7. The method of claim 6 wherein the first gate edge corresponds to a source edge of the gate of the device and the second gate edge corresponds to the drain edge of the gate of the device.

8. The method of claim 1 wherein patterning the gate stack layers leaves the gate dielectric layer remaining on the substrate.

9. The method of claim 1 wherein:

the gate stack layers comprise a hard mask layer over the gate electrode layer; and

patterning the hard mask using the implant mask to remove a portion of the hard mask layer to expose the gate electrode layer; and

implanting ions to form the channel well after patterning the hard mask.

10. The method of claim 9 wherein the hard mask is further patterned to serve as an etch mask of a gate.

11. The method of claim 10 further comprises patterning the gate stack layers with the patterned hard mask to form a gate with first and second gate edges.

12. The method of claim 11 wherein patterning the gate stack layers leaves the gate dielectric layer remaining on the substrate.

13. The method of claim 1 wherein implanting ions comprises a tilt angle implant.

14. The method of claim 1 wherein a tilt angle of the implant is about 1-45°.

15. The method of claim 1 wherein implanting ions comprises multiple tilt angle implants which are rotated about a plane of the substrate.

16. The method of claim 15 wherein a tilt angle of the implant is about 1-45°.

17. The method of claim 1 wherein implanting ions comprises a quad tilt angle implant which is rotated about a plane of the substrate.

18. A method of forming a device comprising:

providing a substrate prepared with an active device region which includes a doped drift well in a first portion of the active device region and gate stack layers of a gate stack comprising at least a gate electrode layer over a gate dielectric layer on the surface of the substrate;

forming an implant mask on the substrate with a mask opening exposing a portion of a top of the gate stack, the mask opening having first and second opposing edges;

implanting ions through the mask opening and gate stack layers into the substrate to form a channel well in the substrate, wherein a first channel edge of the channel well extends beyond the first mask opening edge, wherein a first portion of the channel well is between the first channel edge and the first mask opening edge, the first portion defines a channel with a length L of a device; and

wherein the channel of the device is disposed under a mask portion and a second portion of the channel well is disposed below the mask opening.

19. The method of claim 18 wherein the substrate comprises:

a drift isolation region in the doped drift well; and

a doped deep well in the substrate of the active device region encompassing the doped drift well.

20. A method of forming a device comprising:

providing a substrate prepared with an active device region which includes a doped drift well in a first portion of the active device region and gate stack layers of a gate stack comprising at least a gate electrode layer over a gate dielectric layer on the surface of the substrate;

forming an implant mask on the substrate with a mask opening exposing a portion of a top of the gate stack, the mask opening having first and second opposing edges;

implanting ions through the mask opening and gate stack layers into the substrate to form a channel well in the substrate in a second portion of the active region, wherein a first channel edge of the channel well extends beyond the first mask opening edge, wherein a first portion of the channel well is between the first channel edge and the first mask opening edge, the first portion defines a channel with a length L of a device; and

wherein the channel of the device is disposed under a mask portion and a second portion of the channel well is disposed below the mask opening.

21. The method of claim 20 wherein the doped drift well in the first portion of the active region is contiguous with the doped channel well in the second portion of the active region.

22. The method of claim 20 wherein the doped drift well in the first portion of the active region is separated from the doped channel well in the second portion of the active region by a third portion.