Method of anisotropically etching silicon

• US 5,501,893 A
• Filed: 08/05/1994
• Issued: 03/26/1996
• Est. Priority Date: 12/05/1992
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Schilp, Andrea, Laermer, Franz
• Primary Examiner(s): CLARK, WILLIAM R H
• Application Number:
  US08/284,490
• Time in Patent Office: 599 Days
• Field of Search: 156/625, 156/635, 156/646, 156/645
• US Class Current: 428/161
• CPC Class Codes: B81C 1/00619 Forming high aspect ratio structures having deep steep walls
• CPC Class Codes: B81C 2201/0112 Bosch process
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/30655 comprising alternated and repeated etching and passivation steps, e.g. Bosch process
• CPC Class Codes: H01L 21/3085 characterised by their behaviour during the process, e.g. soluble masks, redeposited masks
• CPC Class Codes: Y10T 428/24521 with component conforming to contour of nonplanar surface

Abstract

A method of anisotropic plasma etching of silicon to provide laterally defined recess structures therein through an etching mask employing a plasma, the method including anisotropic plasma etching in an etching step a surface of the silicon by contact with a reactive etching gas to removed material from the surface of the silicon and provide exposed surfaces; polymerizing in a polymerizing step at least one polymer former contained in the plasma onto the surface of the silicon during which the surfaces that were exposed in a preceding etching step are covered by a polymer layer thereby forming a temporary etching stop; and alternatingly repeating the etching step and the polymerizing step. The method provides a high mask selectivity simultaneous with a very high anisotropy of the etched structures.

Claims

1. A method of anisotropic plasma etching of silicon to provide laterally defined recess structures therein through an etching mask employing a plasma, the method comprising:

a. anisotropic plasma etching in an etching step a surface of the silicon by contact with a reactive etching gas to removed material from the surface of the silicon and provide exposed surfaces;

b. polymerizing in a polymerizing step at least one polymer former contained in the plasma onto the surface of the silicon during which the surfaces that were exposed in a preceding etching step are covered by a polymer layer thereby forming a temporary etching stop; and

c. alternatingly repeating the etching step and the polymerizing step.

2. The method according to claim 1, wherein the polymerization steps are controlled independently of one another.

3. The method according to claim 1, wherein the etching steps are performed without the presence of polymer formers in the plasma.

4. The method according to claim 1, wherein a polymer layer applied during the polymerization step to the laterally defined recess structures is partially restripped during an immediately subsequent etching step.

5. The method according to claim 1, wherein etching removes material from the surface of the silicon to a preselected etching depth, and wherein the etching steps are performed over a preselected period of time which provides the preselected etching depth.

6. The method according to claim 1, wherein polymerizing polymer formers contained in the plasma onto the surface of the silicon provides a polymer layer having a preselected thickness, and wherein the polymerization steps are performed over a preselected period of time which provides the preselected thickness.

7. The method according to claim 1, wherein the silicon is bombarded by an ionic energy during the etching steps.

8. The method according to claim 1, wherein the silicon is alternatingly bombarded by an ionic energy during the polymerization steps.

9. The method according to claim 1, wherein the silicon is bombarded by an ionic energy during the etching steps, and wherein the ionic energy ranges between 1 and 50 eV during the etching steps.

10. The method according to claim 9, wherein the ionic energy ranges between 5 and 30 eV during the etching steps.

11. The method according to claim 1, wherein the silicon is bombarded by an ionic energy during the polymerization steps, and wherein, during the polymerization steps, the ionic energy ranges between 1 and 10 eV.

12. The method according to claim 11, wherein the ionic energy ranges between 4 and 6 eV.

13. The method according to claim 12, wherein the ionic energy is 5 eV.

14. The method according to claim 1, wherein the reactive etching gas is at least one gas that releases fluorine.

15. The method according to claim 1, wherein the reactive etching gas is a mixture of sulfur hexafluoride, SF₆, and argon, Ar.

16. The method according to claim 1, wherein the at least one polymer former contained in the plasma is at least one hydrofluorocarbon.

17. The method according to claim 16, wherein the at least one hydrofluorocarbon has a low fluorine-to-carbon ratio.

18. The method according to claim 1, wherein the at least one polymer former contained in the plasma is a mixture of trifluoromethane, CHF₃, and argon, Ar.

19. The method according to claim 1, wherein the etching steps and polymerization steps employ the recited respective media have gas flows ranging from 0 to 100 sccm and processing pressures ranging from 10 to 100 μ

bar.

20. The method according to claim 1, wherein the plasma is generated with microwave irradiation at an output ranging between 100 and 1500 W.

21. The method according to claim 1, wherein the plasma is generated with microwave irradiation at an output ranging between 300 and 1200 W.

22. The method according to claim 1, wherein the silicon is cooled during at least one of the etching steps and the polymerization steps.

23. The method according to claim 1, wherein the silicon has a rear side, and wherein the rear side of the silicon is acted upon by a helium gas current.

24. The method according to claim 1, wherein a cooled substrate electrode is provided with a thermal contact material, and wherein the silicon is positioned on the thermal contact material.

25. The method according to claim 1, wherein the etching steps and polymerization steps are preformed with a high plasma density of reactive species and ions.

26. The method according to claim 1, wherein the plasma density and the ionic energy are controlled independently of one another.