Method of etching tungsten or tungsten nitride in semiconductor structures

• US 20030003757A1
• Filed: 05/07/2002
• Published: 01/02/2003
• Est. Priority Date: 07/12/2000
• Status: Active Grant

• Current Assignee: Hakeem Oluseyi, Padmapani Nallan
• Original Assignee: Hakeem Oluseyi, Padmapani Nallan
• Inventors: Oluseyi, Hakeem, Nallan, Padmapani
• Granted Patent: US 6,579,806 B2
• Time in Patent Office: Days
• US Class Current: 438/710
• CPC Class Codes: C23F 4/00 Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
• CPC Class Codes: H01L 21/28079 the final conductor layer next to the insulator being a single metal, e.g. Ta, W, Mo, Al
• CPC Class Codes: H01L 21/28088 the final conductor layer next to the insulator being a composite, e.g. TiN
• CPC Class Codes: H01L 21/28123 Lithography-related aspects, e.g. sub-lithography lengths; Isolation-related aspects, e.g. to solve problems arising at the crossing with the side of the device isolation; Planarisation aspects
• CPC Class Codes: H01L 21/32136 using plasmas

Abstract

The present invention relates to a method of etching tungsten or tungsten nitride in semiconductor structures, and particularly to the etching of gate electrodes which require precise control over the etching process. We have discovered a method of etching tungsten or tungsten nitride which permits precise etch profile control while providing excellent selectivity, of at least 175:1, for example, in favor of etching tungsten or tungsten nitride rather than an adjacent oxide layer. Typically, the oxide is selected from silicon oxide, silicon oxynitride, tantalum pentoxide, zirconium oxide, and combinations thereof. The method appears to be applicable to tungsten or tungsten nitride, whether deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD). In particular, an initial etch chemistry, used during the majority of the tungsten or tungsten nitride etching process (the main etch), employs the use of a plasma source gas where the chemically functional etchant species are generated from a combination of sulfur hexafluoride (SF₆) and nitrogen (N₂), or in the alternative, from a combination of nitrogen trifluoride (NF₃), chlorine (Cl₂), and carbon tetrafluoride (CF₄). Toward the end of the main etching process, a second chemistry is used in which the chemically functional etchant species are generated from Cl₂ and O₂. This final portion of the etch process may be referred to as an “overetch” process, since etching is carried out to at least the surface underlying the tungsten or tungsten nitride. However, this second etch chemistry may optionally be divided into two steps, where the plasma source gas oxygen content and plasma source power are increased in the second step.

Claims

1. A method of plasma etching tungsten or tungsten nitride, wherein an etch selectivity of greater than about 75:

1 is obtained relative to an adjacent silicon oxide layer by using a plasma source gas comprising chemically functional etchant species which are generated from Cl₂ and O₂, wherein the volumetric percentage of O₂ in said plasma source gas is at least 35%, and wherein a plasma density is at least 1.6×

10¹¹ e⁻

/cm³.

2. The method of claim 1, wherein said plasma density is obtained by applying a source power of at least 1600 W.

3. The method of claim 1, wherein said etch selectivity is greater than about 100:

1, said volumetric percentage of O₂ is at least 40%, and said plasma density is at least 1.65×

10¹¹ e⁻

/cm³.

4. The method of claim 3, wherein said plasma density is obtained by applying a source power of at least 1650 W.

5. The method of claim 1, wherein said etch selectivity is greater than about 175:

1, said volumetric percentage of O₂ is at least 45%, and said plasma density is at least 1.8×

10¹¹ e⁻

/cm³.

6. The method of claim 5, wherein said plasma density is obtained by applying a source power of at least 1800 W.

7. A method of selectively etching tungsten or tungsten nitride relative to an underlying oxide layer in semiconductor structures, comprising:

plasma etching a first majority portion of said tungsten or tungsten nitride using a first plasma source gas comprising at least one halogen-based chemically functional etchant species; and

plasma etching a remaining portion of said tungsten or tungsten nitride using a second plasma source gas comprising chemically functional etchant species generated from Cl₂ and O₂.

8. The method of claim 7, wherein said underlying oxide is selected from the group consisting of silicon oxide, silicon oxynitride, tantalum pentoxide, zirconium oxide, and combinations thereof.

9. The method of claim 8, wherein said halogen is selected from the group consisting of fluorine, chlorine, and combinations thereof.

10. The method of claim 9, wherein said first majority portion of said plasma etching is carried out using a first plasma source gas selected from the group consisting of a combination of SF₆ and N₂, and a combination of NF₃, Cl₂, and CF₄.

11. The method of claim 9, wherein said underlying oxide comprises silicon oxide, and wherein a volumetric percentage of O₂ in said second plasma source gas is greater than 20% by volume.

12. The method of claim 11, wherein said O₂ volumetric percentage ranges from greater than 20% to about 45%.

13. The method of claim 9, wherein said underlying oxide comprises silicon oxide, and wherein a plasma density of said etchant plasma is at least 8.0×

10¹⁰ e⁻

/cm³.

14. The method of claim 13, wherein said plasma density ranges from about 8.0×

10¹⁰ e⁻

/cm³ to about 3.0×

10¹¹ e⁻

/cm³.

15. The method of claim 14, wherein said plasma density ranges from about 8.0×

10¹⁰ e⁻

/cm³ to about 2.0×

10¹¹ e⁻

/cm³.

16. The method of claim 13, wherein a plasma source power ranges from about 800 W to about 3000 W.

17. The method of claim 16, wherein said plasma source power ranges from about 800 W to about 2000 W.

18. The method of claim 9, wherein said underlying oxide comprises silicon oxide, and wherein said etching which is carried out using said plasma source gas comprising said chemically functional etchant species generated from Cl₂ and O₂ is carried out in two steps, wherein a volumetric concentration of O₂ in a first step ranges from greater than 20% by volume to about 35% by volume, and wherein a volumetric concentration of O₂ in a second step ranges from greater than about 35% by volume to about 45% by volume.

19. The method of claim 9, wherein said underlying oxide comprises tantalum pentoxide, and wherein a volumetric percentage of O₂ in said second plasma source gas ranges from about 20% to about 50%.

20. The method of claim 19, wherein said underlying oxide comprises tantalum pentoxide, and wherein a plasma density of said etchant plasma ranges from about 2.0×

10¹⁰ e⁻

/cm³ to about 1.8×

10¹¹ e⁻

/cm³.

21. The method of claim 20, wherein a plasma source power ranges from about 200 W to about 1800 W.

22. The method of claim 19, wherein said underlying oxide comprises tantalum pentoxide, and a substrate bias power ranges from about 60 W to about 300 W.

24. The method of claim 23, wherein said underlying oxide is selected from the group consisting of silicon oxide, silicon oxynitride, tantalum pentoxide, zirconium oxide, and combinations thereof.

25. The method of claim 24, wherein said first majority portion of said plasma etching is carried out using a first plasma source gas selected from the group consisting of a combination of SF₆ and N₂, and a combination of NF₃, Cl₂, and CF₄.

26. The method of claim 25, wherein said first plasma source gas comprises SF₆ and N₂, and wherein a volumetric ratio of SF₆:

N₂ in said first plasma source gas ranges from about 2;

5 to about 6;

1.

27. The method of claim 24, or claim 25, or claim 26, wherein said underlying oxide comprises silicon oxide, and wherein a volumetric percentage of O₂ in said second plasma source gas is greater than 20% by volume.

28. The method of claim 27, wherein said O₂ volumetric percentage ranges from greater than 20% to about 45%.

29. The method of claim 27, wherein a plasma density of said etchant plasma is at least 8.0×

10¹⁰ e⁻

/cm³.

30. The method of claim 29, wherein said plasma density ranges from about 8.0×

10¹⁰ e⁻

/cm³ to about 3.0×

10¹¹ e⁻

/cm³.

31. The method of claim 30, wherein said plasma density ranges from about 8.0×

10¹⁰ e⁻

/cm³ to about 2.0×

10¹¹ e⁻

/cm³.

32. The method of claim 27, wherein a plasma source power ranges from about 800 W to about 3000 W.

33. The method of claim 32, wherein said plasma source power ranges from about 800 W to about 2000 W.

34. The method of claim 28, wherein a plasma density of said etchant plasma is at least 8.0×

10¹⁰ e⁻

/cm³.

35. The method of claim 34, wherein said plasma density ranges from about 8.0×

10¹⁰ e⁻

/cm³ to about 3.0×

10¹¹ e⁻

/cm³.

36. The method of claim 34, wherein a plasma source power ranges from about 800 W to about 3000 W.

37. The method of claim 24, wherein said underlying oxide comprises silicon oxide, and wherein said etching which is carried out using said plasma source gas comprising chemically functional etchant species generated from Cl₂ and O₂ is carried out in two steps, wherein a volumetric concentration of O₂ in a first step ranges from greater than 20% by volume to about 35% by volume, and wherein the volumetric concentration of O₂ in a second step ranges from greater than about 35% by volume to about 45% by volume.

38. The method of claim 37, wherein a plasma density during said first step ranges from about 8×

10¹⁰ e⁻

/cm³ to about 1.6×

10¹¹ e⁻

/cm³, and wherein a plasma density during said second step ranges from about 1.6×

10¹¹ e⁻

/cm³ to about 3.0×

10¹¹ e⁻

/cm³.

39. The method of claim 37, wherein a plasma source power during said first step ranges from about 800 W to about 1600 W, and wherein a plasma source power during said second step ranges from about 1600 W to about 3000 W.

40. The method of claim 24, wherein said underlying oxide comprises tantalum pentoxide, and wherein a volumetric percentage of O₂ in said second plasma source gas ranges from about 20% to about 50%.

41. The method of claim 40, wherein said underlying oxide comprises tantalum pentoxide, and wherein a plasma density of said etchant plasma ranges from about 2.0×

10¹⁰ e⁻

/cm³ to about 1.8×

10¹¹ e⁻

/cm³.

42. The method of claim 41, wherein a plasma source power ranges from about 200 W to about 1800 W.

43. The method of claim 40, wherein said underlying oxide comprises tantalum pentoxide, and a substrate bias power ranges from about 60 W to about 300 W.

23. A method of selectively etching tungsten or tungsten nitride relative to an underlying oxide layer in semiconductor structures, comprising:

plasma etching a first majority portion of said tungsten or tungsten nitride using a first plasma source gas comprising fluorine species; and

plasma etching a remaining portion of said tungsten or tungsten nitride using a second plasma source gas comprising chemically functional etchant species generated from Cl₂ and O₂.

44. A method of selectively etching tungsten nitride relative to silicon oxide during the etching of semiconductor structures, comprising:

plasma etching a majority portion of said tungsten nitride using a plasma source gas comprising fluorine species; and

plasma etching a remaining portion of said tungsten nitride using a second plasma source gas comprising chemically functional etchant species generated from Cl₂ and O₂, wherein said O₂ concentration is about 35% by volume or greater, and wherein a plasma density of said etchant plasma is about 1.6×

10¹¹ e⁻

/cm³ or greater.

45. The method of claim 44, wherein said first majority portion of said plasma etching is carried out using a first plasma source gas selected from the group consisting of a combination of SF₆ and N₂, and a combination of NF₃, Cl₂, and CF₄.

46. The method of claim 44, wherein said plasma density is created by application of a plasma source power of 1600 W or greater.

47. The method of claim 44, wherein said O₂ concentration is about 40% by volume or greater, and wherein a plasma density of said etchant plasma is about 1.8×

10¹¹ e⁻

/cm³ or greater.

48. The method of claim 47, wherein said plasma density is created by application of a plasma source power of 1800 W or greater.

50. The method of claim 49, wherein said plasma density is obtained by applying a source power within the range of about 200 W to about 1800 W.

51. The method of claim 49, wherein a substrate bias power ranges from about 60 W to about 300 W.

52. The method of claim 51, wherein a substrate bias power ranges from about 60 W to about 200 W.

53. The method of claim 52, wherein a substrate bias power ranges from about 100 W to about 200 W.

58. The method of claim 51, wherein a substrate bias power ranges from about 60 W to about 200 W.

59. The method of claim 52, wherein a substrate bias power ranges from about 100 W to about 200 W.

49. A method of plasma etching tungsten or tungsten nitride, wherein an etch selectivity of greater than about 75:

1 is obtained relative to an adjacent tantalum pentoxide layer by using a plasma source gas comprising chemically functional etchant species which are generated from Cl₂ and O₂, wherein the volumetric percentage of O₂ in said plasma source gas ranges from about 20% to about 50%, and wherein a plasma density ranges from about 2.0×

10¹⁰ e⁻

/cm³ to about 1.8×

10¹¹ e⁻

/cm³.

54. A method of selectively etching tungsten nitride relative to tantalum pentoxide during the etching of semiconductor structures, comprising:

plasma etching a majority portion of said tungsten nitride using a plasma source gas comprising fluorine species; and

plasma etching a remaining portion of said tungsten nitride using a second plasma source gas comprising chemically functional etchant species generated from Cl₂ and O₂, wherein said O₂ concentration ranges from about 20% to about 50% by volume, and wherein a plasma density of said etchant plasma ranges from about 2.0×

10¹⁰ e⁻

/cm³ to about 1.8×

10¹¹ e⁻

/cm³.

55. The method of claim 54, wherein said first majority portion of said plasma etching is carried out using a first plasma source gas selected from the group consisting of a combination of SF₆ and N₂, and a combination of NF₃, Cl₂, and CF₄.

56. The method of claim 54, wherein said plasma density is obtained by applying a source power within the range of about 200 W to about 1800 W.

57. The method of claim 54, wherein a substrate bias power ranges from about 60 W to about 200 W.

60. A semiconductor gate structure comprising a layer of tungsten and an underlying layer of tantalum pentoxide, deposited on a silicon substrate, wherein said tantalum pentoxide layer has thickness of less than about 100 Å

.

61. The semiconductor gate structure of claim 60, wherein said tantalum pentoxide layer has a thickness within the range of about 30 Å

to about 50 Å

.