SiGe rectification process
View Patent ↗A method for forming strain-relaxed SiGe films comprises depositing a graded strained SiGe layer on a substrate in which the concentration of Ge is greater at the interface with the substrate than at the top of the layer. The strained SiGe film is subsequently oxidized, producing a strain-relaxed SiGe film with a substantially uniform Ge concentration across the thickness of the film. The relaxed SiGe layer may be used to form a strained silicon layer on a substrate.
1. A method for forming a strain-relaxed SiGe layer on a substrate comprising:
depositing a reverse graded strained SiGe layer onto a substrate, the reverse graded SiGe layer having a lower surface in contact with the substrate and an upper surface, wherein a first Ge concentration at the lower surface is greater than a second Ge concentration at the upper surface; and
oxidizing the reverse graded SiGe film to produce a strain-relaxed SiGe layer.
2. The method of claim 1 , wherein the substrate comprises a single-crystal silicon substrate.
3. The method of claim 2 , wherein the substrate further comprises an epitaxial silicon layer.
4. The method of claim 1 , wherein the substrate is an SOI substrate.
5. The method of claim 1 , wherein the first Ge concentration is in the range of about 20 atomic % to about 50 atomic % prior to oxidizing.
6. The method of claim 5 , wherein the first Ge concentration is about 40 atomic % prior to oxidizing.
7. The method of claim 1 , wherein the second Ge concentration is in the range of about 0 atomic % to about 10 atomic % prior to oxidizing.
8. The method of claim 7 , wherein the second Ge concentration is about 0 atomic % prior to oxidizing.
9. The method of claim 1 , wherein after oxidizing the Ge concentration in the strain-relaxed SiGe layer varies by less than about 5% between the lower surface and the upper surface.
10. The method of claim 1 , wherein oxidizing comprises exposing the reverse graded SiGe film to an oxidizing agent.
11. The method of claim 10 , wherein the oxidizing agent is selected from the group consisting of water and oxygen.
12. A method of forming a strained silicon layer on a substrate comprising:
depositing a strained SiGe layer comprising a top and a bottom on the substrate, wherein the SiGe layer comprises a reverse graded Ge concentration;
oxidizing the strained SiGe layer thereby forming a silicon oxide layer over a strain-relaxed SiGe layer;
removing the oxide; and
depositing a strained silicon layer over the strain relaxed SiGe layer.
13. The method of claim 12 , wherein the substrate is a bulk silicon wafer.
14. The method of claim 13 , wherein the substrate further comprises an epitaxial silicon layer.
15. The method of claim 12 , wherein the substrate is an SOI substrate.
16. The method of claim 12 , wherein the Ge concentration increases from the top to the bottom prior to oxidizing.
17. The method of claim 12 , wherein oxidizing comprises exposing the substrate to an oxidizing agent.
18. The method of claim 17 , wherein the substrate is exposed to an oxidizing agent at a temperature between about 850° C. and about 1150° C.
19. The method of claim 17 , wherein the substrate is exposed to an oxidizing agent at a temperature greater than about 1000° C.
20. The method of claim 17 , wherein the oxidizing agent is selected from the group consisting of water and oxygen.
21. The method of claim 12 , wherein oxidizing comprises dry oxidation.
22. The method of claim 12 , wherein oxidizing comprises wet oxidation.
23. The method of claim 12 , wherein removing the oxide comprises wet etching.
24. A method for forming a strain-relaxed SiGe layer on a substrate comprising:
depositing a strained SiGe layer onto a substrate, the SiGe layer having a lower surface in contact with the substrate and an upper surface, wherein a first Ge concentration at the lower surface is greater than a second Ge concentration at the upper surface; and
oxidizing the SiGe film to produce a strain-relaxed SiGe layer wherein the concentration of Ge is highest at the lower surface.
25. The method of claim 24 , wherein the Ge concentration decreases linearly from the first concentration to the second concentration prior to oxidizing.