Method of making a semiconductor device having a semiconductor material on a relaxed semiconductor including replacing a strained, selective etchable material, with a low density dielectric in a cavity

1. A method of making a semiconductor device comprising:

applying a mask material to a first region on a substrate, wherein the substrate comprises a crystalline material;

removing substrate from the unmasked substrate adjacent to the first region to form a recessed region;

forming a strained, selectively etchable material in the recessed region;

removing the mask material from the first region;

forming a semiconductor on the selectively etchable material and first region to produce a strained semiconductor layer;

applying mask material to the strained semiconductor layer; forming a trench in the strained semiconductor layer at a distance from the first region wherein the trench extends through the selectively etchable material to the substrate;

removing the selectively etchable material after forming the trench to form a continuous cavity comprising the trench and the area resulting from the removed selectively etchable material;

filling the continuous cavity with low density dielectric;

annealing the strained semiconductor layer and low density electric to produce a relaxed semiconductor; and

forming an additional semiconductor material on the relaxed semiconductor.

2. The method of claim 1 , wherein the selectively etchable material has a thickness of 1 to 5 nanometers.

3. The method of claim 1 , wherein the low density dielectric comprises silicon dioxide having a density of 1.5 g/cm 3 to 3 g/cm 3 .

4. The method of claim 1 , wherein annealing occurs for 1 second to 3 hours at a temperature of 500 to 1300° C.

5. The method of claim 1 , wherein the relaxed semiconductor is silicon germanium having 20 to 25 mole % germanium and the additional semiconductor is silicon germanium having 40 to 50 mole % germanium.

6. The method of claim 1 , wherein the selectively etchable material comprises germanium.

7. The method of claim 1 , further comprising:

applying a mask material to a second region on the substrate;

removing substrate from the unmasked substrate adjacent to the second region to form a second recessed region;

forming the strained, selectively etchable material in the second recessed region;

removing the mask material from the second region;

forming the semiconductor on the selectively etchable material and second region;

applying mask material to the strained semiconductor layer; forming a trench in the strained semiconductor layer at a distance from the first region and the second region wherein the trench extends through the selectively etchable material to the substrate;

removing the selectively etchable material after forming the trench to form a continuous cavity comprising the trench and the area resulting from the removed selectively etchable material;

filling the continuous cavity with low density dielectric;

annealing the strained semiconductor layer and low density electric to produce a relaxed semiconductor; and

forming a second additional semiconductor material on the relaxed semiconductor.

8. A method of making a semiconductor device comprising:

applying a mask material to a first region on a substrate comprising silicon;

removing substrate from the unmasked substrate adjacent to the first region to form a recessed region;

forming a strained, germanium layer in the recessed region; removing the mask material from the first region;

forming silicon germanium on the strained germanium layer and first region to produce a strained silicon germanium layer;

applying mask material to the strained silicon germanium layer;

forming a trench in the strained silicon germanium layer at a distance from the first region wherein the trench extends through the strained germanium region to the substrate;

removing strained germanium after forming the trench to form a continuous cavity area comprising the trench and the area resulting from the removed strained germanium;

filling the continuous cavity with low density silicon oxide; annealing the low density oxide and strained silicon germanium to produce a relaxed silicon germanium; and

forming a semiconductor material on the relaxed silicon germanium.

9. The method of claim 8 , wherein the germanium layer has a thickness of 1 to 2 nanometers.

10. The method of claim 8 , wherein the low density silicon dioxide has a density of 1.5 g/cm 3 to 3 g/cm 3 .

11. The method of claim 8 , wherein annealing occurs for 1 second to 3 hours at a temperature of 500 to 1300° C.

12. The method of claim 8 , wherein the relaxed silicon germanium has a germanium content of 20 to 25 mole %.

13. The method of claim 8 , wherein the semiconductor material comprises silicon germanium having a germanium content of 40 to 50 mole %.

14. The method of claim 8 , wherein the semiconductor material comprises silicon.