Fabrication of devices having different interfacial oxide thickness via lateral oxidation

1. A method for forming a semiconductor device, the method comprising:

forming a first field effect transistor (FET) and a second FET on a substrate, the first FET comprising a first interfacial oxide layer, and the second FET comprising a second interfacial oxide layer;

encapsulating the first interfacial oxide layer of the first FET; and

performing lateral oxidation of the second interfacial oxide layer of the second FET, wherein the lateral oxidation of the second interfacial oxide layer of the second FET converts a portion of the substrate located underneath the second FET into additional interfacial oxide.

2. The method of claim 1 , wherein the first and second interfacial oxide layers comprise one of silicon oxide and silicon oxynitride.

3. The method of claim 1 , wherein the substrate comprises one of silicon and silicon germanium.

4. The method of claim 1 , wherein the lateral oxidation is performed at a temperature from about 400° C. to about 800° C.

5. The method of claim 4 , wherein the lateral oxidation is performed at a temperature of about 700° C.

6. The method of claim 1 , wherein the lateral oxidation is performed for a lateral oxidation time period that is determined based on a gate length of the second FET.

7. The method of claim 1 , wherein encapsulating the first interfacial oxide layer of the first FET comprises depositing an oxidation-resistant material over the first FET.

8. The method of claim 7 , wherein the oxidation-resistant material comprises silicon nitride.

9. The method of claim 1 , further comprising:

forming an oxide liner over the first FET and the second FET;

removing the oxide liner from the first FET;

forming first oxidation-resistant material over the first FET, wherein forming the first oxidation-resistant material over the first FET comprises encapsulating the first interfacial oxide layer of the first FET, and forming second oxidation-resistant material over the oxide liner on the second FET; and

removing a portion of the oxide liner from the second FET to expose the second interfacial oxide layer of the second FET.

10. The method of claim 1 , wherein the lateral oxidation of the second interfacial oxide layer of the second FET further converts a portion of the substrate located adjacent to the second FET in the substrate into excess oxide.

11. The method of claim 10 , further comprising removing the excess oxide from the substrate after the lateral oxidation to form a recess in the substrate adjacent to the second FET.

12. The method of claim 11 , further comprising forming gate and source/drain silicide for the first and second FETs after performing lateral oxidation of the second interfacial oxide layer of the second FET, wherein the source/drain silicide for the second FET is formed in the recess in the substrate adjacent to the second FET.

13. The method of claim 1 , wherein the first FET comprises the first interfacial oxide layer located on the substrate, a first high-k dielectric layer located on the first interfacial oxide layer, and a first gate metal layer located on the first high-k dielectric layer; and

wherein the second FET comprises the second interfacial oxide layer located on the substrate, a second high-k dielectric layer located on the second interfacial oxide layer, and a second gate metal layer located on the second high-k dielectric layer.

14. The method of claim 13 , wherein the first FET further comprises a first gate silicon layer located over the first gate metal layer, and the second FET further comprises a second gate silicon layer located over the second gate metal layer, and further comprising:

siliciding the first and second gate silicon layers after performing lateral oxidation of the second interfacial oxide layer of the second FET.