Multi-metal dipole doping to offer multi-threshold voltage pairs without channel doping for highly scaling CMOS device

1. A method for fabricating a semiconductor device including multiple pairs of threshold voltage (Vt) devices, comprising:

forming a stack on a base structure having a first region corresponding to a first pair of Vt devices, a second region corresponding to a second pair of Vt devices and a third region corresponding to a third pair of Vt devices, the stack including a first dipole layer, a first sacrificial layer formed on the first dipole layer, a second sacrificial layer formed on the first sacrificial layer, and a third sacrificial layer formed on the second sacrificial layer;

exposing the base structure in the third region; and

forming a second dipole layer different from the first dipole layer.

2. The method of claim 1 , wherein the base structure includes a dielectric layer formed on an interfacial layer.

3. The method of claim 1 , wherein the sacrificial layers include a material selected based at least in part on etch resistance properties of materials included in the first dipole layer and the second sacrificial layer.

4. The method of claim 3 , wherein the dipole layers include different materials, or a same material having different thicknesses.

5. The method of claim 1 , wherein exposing the base structure in the third region further includes:

performing a first patterning process, including forming a first resist in the second region;

removing the third sacrificial layer and the first resist from the second region after removing material up to the base structure from the first and third regions;

forming a fourth sacrificial layer;

performing a second patterning process, including forming a second resist on the fourth sacrificial layer in the first region and a third resist on the fourth sacrificial layer in the third region;

removing the second and third resists after removing material up to the first sacrificial layer from the second region;

forming a fifth sacrificial layer and a sixth sacrificial layer on the fifth sacrificial layer;

performing a third patterning process, including forming a fourth resist; and

removing the fourth resist and the sixth sacrificial layer from the first and second regions after removing material up to the base structure from the third region, wherein the second dipole layer is formed on the fifth sacrificial layer.

6. The method of claim 5 , further comprising:

forming a seventh sacrificial layer on the second dipole layer; and

performing a fourth patterning process, including forming a fifth resist on the third region.

7. The method of claim 6 , further comprising:

forming a semiconductor layer and performing a drive-in anneal process after removing the fifth resist;

performing a wet strip; and

forming a set of work function metal layers in each of the regions and a gate electrode on the sets of work function metal layers.

8. The method of claim 7 , wherein the semiconductor layer includes amorphous silicon (a-Si).

9. The method of claim 5 , wherein the base structure further includes a fourth region corresponding to a fourth Vt device, and further comprising:

forming a seventh sacrificial layer on the second dipole layer;

performing a fourth patterning process, including forming a fifth resist on the third region;

forming an eighth sacrificial layer and a ninth sacrificial layer after removing the fifth resist;

performing a fifth patterning process, including forming a sixth resist in the first, second and third regions;

removing material up to the dielectric layer in the fourth region, and the sixth resist and the ninth sacrificial layer from the first, second and third regions; and

forming a third dipole layer different from the first and second dipole layers.

10. The method of claim 9 , further comprising:

forming a tenth sacrificial layer on the third dipole layer;

performing a sixth patterning process, including forming a seventh resist in the fourth region;

removing the tenth sacrificial layer, the eighth sacrificial layer and the seventh resist;

forming a semiconductor layer and performing a drive-in anneal process;

performing a wet strip; and

forming a set of work function metal layers in each of the regions and a gate electrode on the sets of work function metal layers.

11. The method of claim 10 , wherein the semiconductor layer includes amorphous silicon (a-Si).