Method of forming multiple gate insulators on a strained semiconductor heterostructure

1. A method of fabricating semiconductor devices, the method comprising the steps of:

(a) providing a substrate;

(b) fabricating a first semiconductor device on the substrate, the device comprising at least one first strained channel region and a first gate insulator having first thickness, the step comprising:

(i) growing an intermediate portion of the first gate insulator on the substrate by thermal oxidation, and

(ii) depositing a predetermined amount of a dielectric material over the intermediate portion of the first gate insulator thereby increasing thickness thereof to the first thickness;

(c) fabricating a second semiconductor device on the substrate, the device comprising and at least one second strained channel region a second gate insulator having second thickness different from the first thickness, the step comprising:

(i) removing the first gate insulator in a first area of the substrate, and

(ii) forming the second gate insulator in the first area thereover,

wherein thickness of at least one of said the first and second strained channel regions is substantially unchanged following the fabrication of the semiconductor devices.

2. The method of claim 1 , wherein substep (c)(ii) comprises at least one of chemical vapor deposition and thermal oxidation.

3. The method of claim 1 , wherein the at least one strained channel region comprises a semiconductor material selected from the group consisting of Si, Ge, and SiGe.

4. The method of claim 3 , wherein thickness of the strained channel region ranges from approximately 50Å to approximately 300 Å.

5. The method of claim 1 , wherein the substrate comprises an insulator layer.

6. The method of claim 1 , wherein the substrate comprises a relaxed semiconductor layer.

7. The method of claim 6 , wherein the relaxed semiconductor layer comprises SiGe, Ge, or GaAs.

8. The method of claim 1 , wherein the first thickness ranges from approximately 20| to approximately 100 Å.

9. The method of claim 1 , wherein the second thickness ranges from approximately 10Å to approximately 20 Å.

10. The method of claim 1 , wherein the dielectric material comprises SiO 2 .

11. The method of claim 1 , wherein thickness of the intermediate portion of the first gate insulator does not exceed approximately 10 Å.