Thin low defect relaxed silicon germanium layers on bulk silicon substrates
A strain relaxed silicon germanium layer that has a low defect density is formed on a surface of a silicon substrate without causing wafer bowing. The strain relaxed silicon germanium layer is formed using multiple epitaxial growing, bonding and transferring steps. In the present application, a thick silicon germanium layer having a low defect density is grown on a transferred portion of a topmost silicon germanium sub-layer of an initial strain relaxed silicon germanium graded buffer layer and then bonded to a silicon substrate. A portion of the thick silicon germanium layer is then transferred to the silicon substrate. Additional steps of growing a thick silicon germanium layer having a low defect density, bonding and layer transfer may be performed as necessary.
1. A method of forming a semiconductor structure, said method comprising:
forming a silicon germanium graded buffer layer having a first thickness on a surface of a first silicon substrate, wherein said silicon germanium graded buffer layer includes a plurality of silicon germanium sub-layers in which the content of germanium in each of said sub-layers increases from bottom to top;
bonding a topmost silicon germanium sub-layer of said silicon germanium graded buffer layer to a second silicon substrate;
transferring a portion of said topmost silicon germanium sub-layer to said second silicon substrate;
epitaxially growing a silicon germanium layer having a second thickness that is greater than said first thickness on said transferred portion of said topmost silicon germanium sub-layer;
bonding said silicon germanium layer having said second thickness to a third silicon substrate; and
transferring a portion of said silicon germanium layer having said second thickness to said third silicon substrate.
2. The method of claim 1 , further comprising:
epitaxially growing a silicon germanium layer having a third thickness on said transferred portion of said silicon germanium layer having said second thickness;
bonding said silicon germanium layer having said third thickness to a fourth silicon substrate; and
transferring a portion of said silicon germanium layer having said third thickness to said fourth silicon substrate.
3. The method of claim 1 , wherein said forming said silicon germanium graded buffer layer comprises epitaxial growth of said plurality of silicon germanium sub-layers.
4. The method of claim 1 , wherein said topmost silicon germanium sub-layer of said silicon germanium graded buffer layer has a germanium content from 20 atomic percent germanium to 25 atomic percent germanium, and a thickness from 2 micrometers to 4.5 micrometers.
5. The method of claim 3 , wherein said silicon germanium layer of said second thickness has a germanium content from 20 atomic percent germanium to 25 atomic percent germanium.
6. The method of claim 1 , wherein said transferred portion of said silicon germanium layer having said second thickness is from 50 nm to 1000 nm thick.
7. The method of claim 6 , wherein said transferred portion of said silicon germanium layer having said second thickness has a defect density of less than 100 defect atoms/cm 2 .
8. The method of claim 6 , wherein said transferred portion of said silicon germanium layer having said second thickness is void of threading dislocation defects.
9. The method of claim 1 , wherein said transferring said portion of said topmost silicon germanium sub-layer comprises forming a weakened or bubble region in said topmost silicon germanium sub-layer by ion implantation.
10. The method of claim 1 , wherein said transferring said portion of said topmost silicon germanium sub-layer comprises a material removal process.
11. The method of claim 1 , wherein said transferring said portion of said silicon germanium layer having said second thickness comprises forming a weakened or bubble region in said silicon germanium layer having said second thickness by ion implantation.
12. The method of claim 1 , wherein said transferring said portion of said silicon germanium layer having said second thickness comprises a material removal process.
13. The method of claim 2 , wherein said silicon germanium layer of said third thickness has a germanium content from 20 atomic percent germanium to 25 atomic percent germanium.
14. The method of claim 13 , wherein said transferred portion of said silicon germanium layer having said third thickness is from 50 nm to 1000 nm thick.