Fabrication of strained heterojunction structures

• US 20060134893A1
• Filed: 12/16/2004
• Published: 06/22/2006
• Est. Priority Date: 12/16/2004
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Lagally, Max G., Savage, Donald E., Roberts, Michelle M.
• Granted Patent: US 7,229,901 B2
• Time in Patent Office: Days
• US Class Current: 438/483
• CPC Class Codes: H01L 21/6835 using temporarily an auxiliary support
• CPC Class Codes: H01L 21/76256 using silicon etch back techniques, e.g. BESOI, ELTRAN
• CPC Class Codes: H01L 21/84 the substrate being other than a semiconductor body, e.g. being an insulating body
• CPC Class Codes: H01L 2221/6835 used as a support during build up manufacturing of active devices
• CPC Class Codes: H01L 29/0657 characterised by the shape of the body

Abstract

Growth of multilayer films is carried out in a manner which allows close control of the strain in the grown layers and complete release of the grown films to allow mounting of the released multilayer structures on selected substrates. A layer of material, such as silicon-germanium, is grown onto a template layer, such as silicon, of a substrate having a sacrificial layer on which the template layer is formed. The grown layer has a lattice mismatch with the template layer so that it is strained as deposited. A top layer of crystalline material, such as silicon, is grown on the alloy layer to form a multilayer structure with the grown layer and the template layer. The sacrificial layer is preferentially etched away to release the multilayer structure from the sacrificial layer, relaxing the grown layer and straining the crystalline layers interfaced with it.

Claims

1. A method of forming a strained crystalline layer on which devices may be formed comprising:

(a) growing a layer of material on a side of a crystalline template layer to form a multilayer structure, the template layer supported on its other side by a sacrificial layer of a substrate having a handle layer, the grown layer and the template layer having a lattice mismatch so that the grown layer is strained as it is grown;

(b) patterning and etching material adjacent to a side of the sacrificial layer to expose areas of the sacrificial layer; and

(c) preferentially etching the sacrificial layer at the exposed areas of the sacrificial layer to release the multilayer structure such that the strain in the grown layer is relaxed and the crystalline template layer is strained as the grown layer relaxes.

2. The method of claim 1 wherein the step of patterning and etching is carried out through the multilayer structure to the sacrificial layer using lithographic patterning and etching.

3. The method of claim 2 wherein the patterning isolates discrete sections of the multilayer structure so that the preferential etching of the sacrificial layer releases the multilayer structure in multiple individual sections.

4. The method of claim 2 wherein the patterning is carried out to form isolated openings so that preferentially etching the sacrificial layer releases the multilayer structure as a continuous mesh film with openings therein.

5. The method of claim 1 further including growing a top layer of crystalline material on the grown layer to form part of the multilayer structure before patterning and etching.

6. The method of claim 5 including growing another layer of material over the top crystalline layer before carrying out patterning and etching.

7. The method of claim 1 wherein patterning and etching is carried out through the substrate handle layer to the sacrificial layer using lithographic patterning and etching.

8. The method of claim 1 further including mounting the released multilayer structure onto a substrate.

9. The method of claim 1 wherein the template layer is less than 100 nm in thickness.

10. The method of claim 1 wherein the grown layer is grown epitaxially to a thickness below an effective critical thickness at which the grown layer will start to relax plastically and generate dislocations.

11. The method of claim 1 wherein the step of preferentially etching the sacrificial layer is carried out using a liquid etchant.

12. The method of claim 1 wherein the step of preferentially etching the sacrificial layer is carried out using a vapor phase etchant.

13. The method of claim 1 further including mounting the released multilayer structure onto the surface of a second sacrificial layer carried on an underlying handle layer, depositing a second layer of material on the exposed top crystalline layer of the multilayer structure, depositing crystalline material on the second alloy layer to form a multilayer laminate, patterning and etching the multilayer laminate to the second sacrificial layer, and preferentially etching the sacrificial layer to release the laminate.

14. The method of claim 13 wherein the steps of claim 13 are carried out two or more times.

15. The method of claim 1 wherein before the step of growing a layer of material the template layer is in strain.

16. The method of claim 15 wherein the template layer is the top layer of a strained-silicon-on-insulator substrate.

17. A method of forming a strained crystalline silicon layer on which devices may be formed comprising:

(a) growing a layer of silicon-germanium alloy on a side of a silicon template layer of a silicon-on-insulator substrate to form a multilayer structure, the silicon-on-insulator substrate including the silicon template layer supported on its other side on a sacrificial layer of silicon dioxide formed over a silicon handle layer, such that the silicon-germanium alloy layer is in compressive strain as it is grown;

(b) patterning and etching material adjacent to a side of the sacrificial layer to expose areas of the sacrificial layer; and

(c) preferentially etching the silicon dioxide sacrificial layer to release the multilayer structure such that strain in the silicon-germanium layer is relaxed and the silicon template layer is strained as the silicon-germanium layer relaxes.

18. The method of claim 17 wherein the step of patterning and etching is carried out through the multilayer structure to the silicon dioxide sacrificial layer using lithographic patterning and etching.

19. The method of claim 18 wherein the patterning isolates discrete sections of the multilayer structure so that the preferential etching of the silicon dioxide layer releases the multilayer structure in multiple individual sections.

20. The method of claim 18 wherein the patterning is carried out to form isolated openings so that preferentially etching the silicon dioxide layer releases the multilayer structure as a continuous mesh film with openings therein.

21. The method of claim 18 further including growing a top layer of crystalline silicon on the layer of silicon-germanium to form a multilayer semiconductor structure with the silicon-germanium layer and the silicon template layer.

22. The method of claim 17 further including depositing another layer of silicon-germanium over the top silicon layer before carrying out patterning and etching.

23. The method of claim 17 wherein patterning and etching is carried out through the substrate handle layer to the sacrificial layer using lithographic patterning and etching.

24. The method of claim 17 further including mounting the released multilayer structure onto a substrate.

25. The method of claim 17 wherein the silicon template layer is less than 100 nm in thickness.

26. The method of claim 17 wherein the silicon-germanium layer deposited on the silicon template layer is grown epitaxially to a thickness below an effective critical thickness at which the silicon-germanium layer will start to relax plastically and generate dislocations.

27. The method of claim 17 wherein silicon template layer is initially unstrained and the silicon-germanium layer has a germanium content of up to about 18%.

28. The method of claim 17 wherein the step of preferentially etching the silicon dioxide layer is carried out using a liquid etchant.

29. The method of claim 28 wherein the liquid etchant is HF.

30. The method of claim 17 wherein the step of preferentially etching the silicon dioxide layer is carried out using a vapor phase etchant.

31. The method of claim 30 wherein the vapor phase etchant is HF vapor.

32. The method of claim 17 wherein the deposit of the silicon-germanium layer is carried out by molecular beam epitaxy, chemical vapor deposition, or sputter deposition, and wherein the step of depositing the top silicon layer on the silicon-germanium layer is carried out by molecular beam epitaxy, chemical vapor deposition, or sputter deposition.

33. The method of claim 17 wherein the silicon-on-insulator substrate comprises a crystalline silicon handle layer, the silicon dioxide sacrificial layer on the silicon handle layer, and the silicon template layer on the silicon dioxide sacrificial layer.

34. The method of claim 17 further including mounting the released multilayer structure including a first silicon-germanium layer onto the surface of a silicon dioxide sacrificial layer carried on an underlying handle layer, depositing a second layer of silicon-germanium on the top silicon layer of the multilayer structure, depositing crystalline silicon on the second silicon-germanium layer to form a multilayer laminate, and preferentially etching the silicon dioxide sacrificial layer to release the laminate.

35. The method of claim 34 wherein the second silicon-germanium layer has a higher germanium content than the first silicon-germanium layer.

36. The method of claim 34 wherein the steps of claim 34 are carried two or more times.

37. The method of claim 36 wherein each subsequently deposited silicon-germanium layer has a higher germanium content than any previously deposited silicon-germanium layer.

38. The method of claim 17 wherein before the step of growing a layer of silicon-germanium alloy, the silicon template layer is in tensile strain.

39. The method of claim 38 wherein the silicon-germanium layer has a germanium content of at least 18%.

40. A strained multilayer semiconductor structure comprising:

(a) a bottom layer of tensilely strained crystalline silicon;

(b) a layer of partially compressive-strain relaxed silicon-germanium alloy on the bottom silicon layer; and

(c) a top layer of tensilely strained crystalline silicon on the silicon-germanium layer.

41. The semiconductor structure of claim 40 further including a layer of silicon-germanium on the top silicon layer.

42. The semiconductor structure of claim 40 further including a substrate on which the bottom silicon layer is supported.

43. The semiconductor structure of claim 42 wherein the substrate is crystalline silicon.

44. The semiconductor structure of claim 40 wherein the silicon-germanium layer is at least 50 nm thick.

45. The semiconductor structure of claim 40 wherein the silicon-germanium layer has a germanium content of between 5% and 18%.

46. The semiconductor structure of claim 40 wherein the silicon-germanium layer is free of dislocations and has a germanium content greater than 18%.

47. The semiconductor structure of claim 40 including a second partially compressive strain relaxed silicon-germanium alloy layer on the top silicon layer and a second tensilely strained layer of silicon on the second silicon-germanium layer, wherein the germanium content of the second silicon-germanium layer is higher than that of the first silicon-germanium layer.

48. A strained multilayer semiconductor structure comprising:

(a) a bottom layer of tensilely strained crystalline silicon;

(b) a first layer of partially compressive strain relaxed silicon-germanium alloy on the bottom silicon layer;

(c) a second layer of tensilely strained crystalline silicon on the first silicon-germanium layer;

(d) a second layer of partially compressive strain relaxed silicon-germanium alloy on the second layer of tensilely strained silicon, wherein the Ge content in the second silicon-germanium alloy layer is the same as or higher than that in the first silicon-germanium alloy layer; and

(e) a layer of tensilely strained crystalline silicon on the second silicon-germanium alloy layer.

49. A method of forming a strained crystalline layer on which devices may be formed comprising:

(a) growing a first layer of material epitaxially on a side of a crystalline template layer to a thickness below an effective critical thickness at which the grown layer will start to relax plastically and generate dislocations, the template layer supported on its other side by a sacrificial layer of a substrate having a handle layer, the first grown layer and the template layer having a lattice mismatch so that the grown layer is compressively strained as it is grown;

(b) growing a top layer of material epitaxially over the first grown layer to a thickness below an effective thickness at which the top layer will start to relax plastically and generate dislocations, the first and top layers forming a multilayer structure with the template layer;

(c) patterning and etching material adjacent to a side of the sacrificial layer to expose areas of the sacrificial layer; and

(d) preferentially etching the sacrificial layer at the exposed areas of the sacrificial layer to release the multilayer structure such that the strain in the first grown layer is relaxed and the crystalline template layer and top layer are strained as the first grown layer relaxes.

50. The method of claim 49 wherein the step of patterning and etching is carried out through the multilayer structure to the sacrificial layer using lithographic patterning and etching.

51. The method of claim 50 wherein the patterning isolates discrete sections of the multilayer structure so that the preferential etching of the sacrificial layer releases the multilayer structure in multiple individual sections.

52. The method of claim 50 wherein the patterning is carried out to form isolated openings so that preferentially etching the sacrificial layer releases the multilayer structure as a continuous mesh film with openings therein.

53. The method of claim 49 including epitaxially growing another layer of material over the top crystalline layer before carrying out patterning and etching.

54. The method of claim 49 wherein patterning and etching is carried out through the substrate handle layer to the sacrificial layer using lithographic patterning and etching.

55. The method of claim 49 further including mounting the released multilayer structure onto a substrate.

56. The method of claim 49 wherein the step of preferentially etching the sacrificial layer is carried out using a liquid etchant.

57. The method of claim 49 wherein the step of preferentially etching the sacrificial layer is carried out using a vapor phase etchant.

58. The method of claim 49 further including mounting the released multilayer structure onto the surface of a second sacrificial layer carried on an underlying handle layer, depositing a second layer of material on the exposed top crystalline layer of the multilayer structure, depositing crystalline material on the second layer to form a multilayer laminate, patterning and etching the multilayer laminate to the second sacrificial layer, and preferentially etching the sacrificial layer to release the laminate.

59. The method of claim 58 wherein the steps of claim 58 are carried out two or more times.

60. The method of claim 49 wherein the template layer is crystalline silicon supported on a silicon dioxide sacrificial layer on a silicon handle layer, the first grown layer is silicon-germanium, and the top layer is crystalline silicon.