Method of depositing high-quality SiGe on SiGe substrates
This invention provides a method of depositing high-quality Si or SiGe epitaxial layers on SiGe substrates. By first depositing a thin Si seed layer on the SiGe substrate, the quality of the seed layer and of the subsequently deposited layers is greatly improved over what is obtained from depositing SiGe directly onto the SiGe substrate. Indeed, whereas the RMS surface roughness of the deposition of SiGe directly on SiGe, as measured by atomic-force microscopy (AFM), was 3–4 nm, it was more than an order of magnitude better when a thin Si seed layer was employed. This work was performed on an ultra-high-vacuum chemical vapor deposition (UHV/CVD) system; however, the same method would apply to other deposition systems such as atmospheric-pressure, low-pressure and rapid-thermal CVD.
1. A method of depositing at least one epitaxial layer of SiGe on to a SiGe substrate comprising firstly depositing on the SiGe substrate a thin Si seed layer and then depositing on the Si seed layer the epitaxial layer of SiGe.
2. A method according to claim 1 , wherein the fraction of Ge, X %, within the SiGe substrate is different from the fraction of Ge, Y %, within the at least one SiGe epitaxial layer.
3. A method according to claim 2 , wherein the seed layer has a thickness 10 A<t<500 A.
4. A method according to claim 3 , wherein t=substantially 100 A.
5. A method according to claim 2 , wherein the SiGe substrate has exposed regions of SiGe and oxide and the seed layer is deposited on the exposed areas of SiGe and oxide.
6. A method according to claim 2 , wherein the SiGe in the SiGe substrate is doped.
7. A method according to claim 2 , wherein the SiGe in the at least one SiGe epitaxial layer is doped.
8. A device formed by the method of claim 2 .
9. A method according to claim 1 , wherein the seed layer has a thickness 10 A<t<500 A.
10. A method according to claim 9 , wherein t=substantially 100 A.
11. A method according to claim 10 , wherein the SiGe substrate has exposed regions of SiGe and oxide and the seed layer is deposited on the exposed areas of SiGe and oxide.
12. A method according to claim 9 , wherein the SiGe substrate has exposed regions of SiGe and oxide and the seed layer is deposited on the exposed areas of SiGe and oxide.
13. A method according to claim 9 , wherein the SiGe in the SiGe substrate is doped.
14. A method according to claim 9 , wherein the SiGe in the at least one SiGe epitaxial layer is doped.
15. A method according to claim 1 , wherein the SiGe substrate has exposed regions of SiGe and oxide and the seed layer is deposited on the exposed areas of SiGe and oxide.
16. A method according to claim l, wherein the SiGe in the SiGe substrate is doped.
17. A method according to claim 1 , wherein the SiGe in the at least one SiGe epitaxial layer is doped.
18. A device formed by the method of claim 1 .
19. A method of depositing at least one Si epitaxial layer onto a SiGe substrate comprising depositing on the SiGe substrate a thin Si seed layer and then depositing on the Si seed layer the at least one Si epitaxial layer.
20. A device formed by the method of claim 19 .