Anisotropic polysilicon plasma etch using fluorine gases

• US 5,453,156 A
• Filed: 11/01/1994
• Issued: 09/26/1995
• Est. Priority Date: 11/01/1994
• Status: Expired due to Term

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: Cher, Ming-Shry, Shan, Chung-Hsing
• Primary Examiner(s): DANG, THI D
• Application Number:
  US08/332,907
• Time in Patent Office: 329 Days
• Field of Search: 156/651.1, 156/646.1, 156/643.1, 156/662.1
• US Class Current: 438/695
• CPC Class Codes: H01L 21/32137 of silicon-containing layers

Abstract

A process for dry etching a polysilicon layer or gate structure of an integrated circuit is achieved. More particularly, a process for overetching a polysilicon layer using, in place of a conventional chloride gas (e.g., CCl₄), a fluorine gas, such as C₂ F₆ or CF₄ is disclosed. After the main etch step, a passivation formation step is performed where a mixture of helium and fluorine gases is flowed into a plasma etch chamber. Next, an overetch is performed by flowing a mixture of helium and chlorine gas. This process eliminates the need to use CCl₄ or other harmful ozone containing gases in the overetch step. Moreover, an acceptable polysilicon sidewall profile is achieved and no undercutting of the polysilicon layer is experienced using this process.

Claims

1. The process of etching a polysilicon gate on a suitable substrate through a patterned resist layer which will not undercut the polysilicon layer which process comprises:

etching said polysilicon layer with a first flow of helium and fluorine containing gases into a plasma reactive etching chamber containing said semiconductor substrate;

etching said polysilicon layer with a second flow of helium and chlorine gases into the plasma reactive etching chamber containing said semiconductor substrate;

detecting the endpoint of the completion of etching of the polysilicon layer and stopping the flow of said chlorine gas;

etching said polysilicon layer with a third flow of mixture of fluorine containing gas and helium gases into the plasma reactive etching chamber containing said semiconductor substrate; and

etching said polysilicon layer with a fourth flow of helium and chlorine gases into the plasma reactive etching chamber containing said semiconductor substrate to thereby etch and pattern portions of the polysilicon layer forming the polysilicon gate.

2. The process of claim 1 wherein said substrate is a silicon wafer having an overlying oxide layer with a thickness of approximately 100 Å

.

3. The process of claim 1 wherein during the first flow of fluoride and helium gases the flow rate of the fluorine gas is between about 170 to 180 sccm and the flow rate of the helium gas is between about 145 to 155 sccm.

4. The process of claim 1 wherein during the first flow of fluorine and helium gases the radio frequency power applied is about 325 watts.

5. The process of claim 1 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said first flow of fluorine and helium gases has a vacuum of about 600 mTorr and a temperature of about 120°

C.

6. The process of claim 1 wherein during the second flow of chlorine and helium gases the flow rate of the chlorine gas is between about 125 to 135 sccm and the flow rate of the helium gas is between about 65 to 75 sccm.

7. The process of claim 1 wherein during the second flow of chlorine and helium gases the radio frequency power applied is about 200 watts.

8. The process of claim 1 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said second flow of chlorine and helium gases has a vacuum of about 200 mTorr and a temperature of about 120°

C.

9. The process of claim 1 wherein during the third flow of fluoride and helium gases the flow rate of the chlorine gas is between about 95 to 105 sccm and the flow rate of the helium gas is between about 95 to 105 sccm.

10. The process of claim 1 wherein during the third flow of fluorine and helium gases the radio frequency power applied is about 225 watts.

11. The process of claim 1 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said third flow of fluorine and helium gases has a vacuum of about 900 mTorr and a temperature of about 120°

C.

12. The process of claim 1 wherein during the third flow of fluorine and helium gases said fluorine gas is a gas selected from the group consisting of C₂ F₆, and CF₄.

13. The process of claim 1 wherein during the fourth flow of chlorine and helium gases the flow rate of the chlorine gas is between about 125 to 135 sccm and the flow rate of the helium gas is between about 65 to 75 sccm.

14. The process of claim 1 wherein during the fourth flow of chlorine and helium gases the radio frequency power applied is about 200 watts.

15. The process of claim 1 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said fourth flow of chlorine and helium gases has a vacuum of about 200 mTorr and a temperature of about 120°

C.

16. The process of etching a polysilicon gate from a polysilicon layer on a suitable substrate through a patterned resist layer that exposes portions of the polysilicon layer in a plasma reactive etch chamber which minimizes undercutting of the polysilicon layer, which process comprises:

etching said polysilicon layer so to remove the majority of the exposed polysilicon layer;

etching said polysilicon layer with a passivation formation etch step with the use of an etch gas comprising a mixture of fluorine containing gas and helium gases in the plasma reactive etching chamber containing said semiconductor wafer; and

etching said polysilicon layer with an overetch step with the use of an etch gas comprising helium and chlorine gases in the plasma reactive etching chamber containing said semiconductor wafer.

17. The process of claim 16 wherein said substrate is a silicon wafer having an overlying native oxide layer with a thickness of approximately 100 Å

.

18. The process of claim 16 wherein during the passivation formation etch step the flow rate of the fluorine gas is between about 95 to 105 sccm and the flow rate of the helium gas is between about 95 to 105 sccm.

19. The process of claim 16 wherein during the passivation formation etch step the radio frequency power applied is about 225 watts.

20. The process of claim 16 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said passivation formation etch step has a vacuum of about 900 mTorr and a temperature of about 120°

C.

21. The process of claim 16 wherein during the passivation formation etch step said fluorine gas is a gas selected from the group consisting of C₂ F₆, and CF₄.

22. The process of claim 16 wherein during the overetch step the flow rate of the chlorine gas is between about 125 to 135 sccm and the flow rate of the helium gas is between about 65 to 75 sccm.

23. The process of claim 16 wherein during the overetch step the radio frequency power applied is about 200 watts.

24. The process of claim 16 wherein said etch chamber is a vacuum chamber and the vacuum chamber during said overetch step has a vacuum of about 200 mTorr and a temperature of about 120°

C.