MOS devices with reduced recess on substrate surface

1. A semiconductor device comprising:

a substrate;

a gate structure overlying the substrate, the gate structure comprising a gate dielectric over the substrate and a gate electrode over the gate dielectric;

a lightly doped drain/source (LDD) region substantially aligned with an edge of the gate structure;

a sidewall spacer on a sidewall of the gate structure;

a doped source/drain region formed into the substrate spaced apart from the sidewall spacer having a depth into the substrate substantially greater than about 30 nanometers;

a recessed region having a recess depth of substantially less than about 30 Å in the substrate, wherein at least a portion of the recessed region is under the sidewall spacer; and

a silicon alloy region extending into and contained by the doped source/drain region and adjacent the recessed region, wherein the silicon alloy region has a substantially greater lattice constant than the substrate, and a thickness of substantially greater than about 30 nm;

wherein the silicon alloy region is spaced apart from the LDD region by a portion of the doped source/drain region.

2. The semiconductor device of claim 1 , wherein the gate spacer covers a portion of the silicon alloy region.

3. The semiconductor device of claim 1 , wherein the gate dielectric has a k value of greater than about 3.9.

4. The semiconductor device of claim 1 , wherein the gate electrode comprises a metal silicide.

5. The semiconductor device of claim 1 , wherein the silicon alloy region comprises a p-type impurity.

6. The semiconductor device of claim 1 , wherein the silicon alloy region comprises SiGe.

7. The semiconductor device of claim 1 , wherein the silicon alloy region comprises a portion above a top surface of the substrate.

8. A semiconductor structure comprising:

a substrate;

a first gate structure of a first transistor overlying the substrate, the first transistor being of a first conductivity type, the first gate structure comprising a gate dielectric overlying the substrate and a gate electrode overlying the gate dielectric;

a lightly doped source/drain (LDD) region substantially aligned with an edge of the gate structure;

a first gate spacer on a sidewall of the first gate structure;

a first recessed region of the substrate having a first recess depth of substantially less than about 30 Å, wherein the first recessed region has a top surface adjoining a bottom surface of the first gate spacer;

a first source/drain doped region in the substrate spaced from the sidewall of the first gate structure, the first source/drain region comprising and entirely containing a silicon alloy region having a substantially greater lattice constant than the substrate, wherein the silicon alloy region is spaced apart from the LDD region by a portion of the first source/drain doped region;

a second gate structure of a second transistor overlying the substrate, the second transistor being of a second conductivity type opposite the first conductivity type;

a second source/drain doped region in the substrate and formed in alignment to a sidewall of the second gate structure;

a second gate spacer on a sidewall of the second gate structure; and

a second recessed region comprising at least a portion of the second source/drain doped region, wherein a portion of the second recessed region has a second recess depth of substantially less than about 30 Å, and wherein the portion of the second recessed region has a top surface adjoining a bottom surface of the second gate spacer.

9. The semiconductor structure of claim 8 , wherein the first conductivity type is p-type and the second conductivity type is n-type.

10. The semiconductor structure of claim 8 , wherein the silicon alloy region comprises a portion substantially higher than a top surface of the substrate.

11. The semiconductor structure of claim 8 , wherein the silicon alloy region comprises SiGe.

12. The semiconductor structure of claim 8 , wherein the first source/drain doped region is of p-type, and the second source/drain doped region is of n-type, and wherein the first recessed region has a width of between about 100 Å and about 300 Å, and wherein the second recessed region has a width of greater than about 300 Å.