Implant isolated devices and method for forming the same

1. A method comprising:

forming a gate dielectric layer over a semiconductor substrate;

forming a first gate electrode layer over the gate dielectric layer;

forming a hardmask layer over the first gate electrode layer;

forming an opening in the hardmask layer to expose the first gate electrode layer;

implanting an impurity, wherein the impurity penetrates through the gate dielectric layer to form an implant isolation region in the semiconductor substrate surrounding an active region of the semiconductor substrate;

etching the first gate electrode layer in the opening to expose the gate dielectric layer;

filling the opening with a dielectric material; and,

removing the hardmask layer and dielectric material above the first gate electrode layer.

2. The method of claim 1 , further comprising forming a second gate electrode layer over the first gate electrode layer and patterning a gate electrode.

3. The method of claim 1 , wherein the forming an opening in the hardmask layer comprises removing a portion of the first gate electrode layer at a bottom of the opening in the hardmask layer.

4. The method of claim 1 , wherein the removing the hardmask layer and dielectric material comprises planarizing and wet etching.

5. The method of claim 1 , further comprising depositing a conformal dielectric layer in the opening before implanting an impurity.

6. The method of claim 1 , wherein the hardmask layer and the dielectric material are a same material.

7. The method of claim 1 , wherein the first gate electrode layer is polysilicon.

8. The method of claim 1 , further comprising:

forming a source and a drain region in the active region; and

forming a source contact and a drain contact overlapping the source and the drain regions, respectively.

9. The method of claim 1 , further comprising:

forming a photodiode in the active region.

10. The method of claim 1 , wherein the active region comprises a plurality of active regions, and the implant isolation region comprises a plurality of implant isolation regions, wherein each of the plurality of active regions is surrounded by one of the plurality implant isolation regions and the plurality of active regions are connected to form an image sensor.

11. The method of claim 1 , wherein the implanting an impurity comprises implanting at an implantation energy greater than about 50 keV.

12. A method comprising:

forming over a semiconductor substrate a gate stack comprising a gate dielectric and a first gate electrode layer;

forming a patterned hardmask over the gate stack;

removing an upper portion of the gate stack to form an opening therein, while leaving remaining a lower portion of the gate stack;

implanting an impurity through the remaining lower portion of the gate stack;

filling the opening with a dielectric material on the remaining lower portion of the gate stack; and

removing any remaining hardmask layer and dielectric material above the gate stack, while leaving the dielectric material in the opening; and

forming over the first gate electrode layer and over the dielectric material in the opening, a second gate electrode layer.

13. The method of claim 12 , wherein the first gate electrode layer overlies the gate dielectric and the step of removing an upper portion of the gate stack to form an opening therein, while leaving remaining a lower portion of the gate stack includes etching through the first gate electrode layer, while leaving the gate dielectric remaining.

14. The method of claim 12 , wherein the first gate electrode layer overlies the gate dielectric and the step of removing an upper portion of the gate stack to form an opening therein, while leaving remaining a lower portion of the gate stack includes etching through the first gate electrode and partially through the gate dielectric, while leaving a portion of the gate dielectric remaining.

15. The method of claim 12 , wherein the first gate electrode layer overlies the gate dielectric and the step of removing an upper portion of the gate stack to form an opening therein, while leaving remaining a lower portion of the gate stack includes etching partially through the first gate electrode while leaving a portion of the first gate electrode layer remaining and while leaving the gate dielectric remaining.

16. The method of claim 15 , further comprising removing the portion of the first gate electrode layer remaining after the step of implanting an impurity through the remaining lower portion of the gate stack.

17. The method of claim 15 wherein the step of implanting an impurity through the remaining lower portion of the gate stack forms an implant isolation region in the semiconductor substrate surrounding an active region of the semiconductor substrate.

18. A method comprising:

forming a gate stack over a substrate, the gate stack including a first gate electrode layer;

forming a trench that extends from a topmost surface of the gate stack into the gate stack;

implanting an impurity into the substrate using the gate stack and the trench as a mask, the impurity being implanted into the substrate beneath a bottom of the trench and not beneath the topmost surface of the gate stack;

completely filling the trench with a dielectric material; and

forming a second gate electrode layer over the dielectric material and the first gate electrode layer.

19. The method of claim 18 , wherein the step of forming a trench that extends from a topmost surface of the gate stack into the gate stack includes forming the trench through the first gate electrode layer.

20. The method of claim 18 , wherein the step of forming a trench that extends from a topmost surface of the gate stack into the gate stack includes forming the trench through the first gate electrode layer and at least partially through a gate dielectric underlying the first gate electrode layer.