Method for etching metal silicide with high selectivity to polysilicon

• US 5,880,033 A
• Filed: 06/17/1996
• Issued: 03/09/1999
• Est. Priority Date: 06/17/1996
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Tsai, Hui-Ing
• Primary Examiner(s): Chapman, Mark
• Application Number:
  US08/664,576
• Time in Patent Office: 995 Days
• Field of Search: 438/710, 438/714, 438/719, 438/721, 216/67, 216/72
• US Class Current: 438/710
• CPC Class Codes: H01L 21/32137 of silicon-containing layers

Abstract

A method for etching metal silicide layers 22a, 22b and polysilicon layers 24a, 24b on a substrate 20 with high etching selectivity, and anisotropic etching properties, is described. In the method, the substrate 20 is placed in a plasma zone 55, and process gas comprising Cl₂, O₂, and N₂, is introduced into the plasma zone. A plasma is formed from the process gas to selectively etch the metal silicide layer 22 at a first etch rate that is higher than a second rate of etching of the polysilicon layer 24, while providing substantially anisotropic etching of the metal silicide and polysilicon layers. Preferably, the plasma is formed using combined inductive and capacitive plasma sources.

Claims

1. A method for etching a substrate comprising metal silicide and polysilicon layers, the method comprising the steps of:

(a) placing the substrate in a plasma zone;

(b) introducing into the plasma zone, a process gas comprising Cl₂, O₂ and N₂ and forming a plasma from the process gas, wherein the volumetric flow ratio of Cl₂, O₂, and N₂ is selected to etch the metal silicide layer at a first etch rate that is at least 1.2 times higher than a second rate of etching of the polysilicon layer, while providing substantially anisotropic etching of the metal silicide and polysilicon layers.

2. The method of claim 1, wherein the volumetric flow ratio of Cl₂, O₂, and N₂ is selected to etch the metal silicide and polysilicon layers to form etched features that have sidewalls that form angles of at least about 88°

with a surface of the substrate.

3. The method of claim 1, wherein the volumetric flow ratio of O₂ :

N₂ is from about 0.25;

1 to about 5;

1.

4. The method of claim 3, wherein the volumetric flow ratio of O₂ :

N₂ is from about 0.5;

1 to about 3;

1.

5. The method of claim 1, wherein the ratio of the volumetric flow of Cl₂ to the combined volumetric flow of O₂ and N₂ is from about 5:

1 to about 20;

1.

6. The method of claim 5, wherein the ratio of the volumetric flow of Cl₂ to the combined volumetric flow of O₂ and N₂ is from about 7:

1 to about 15;

1.

7. The method of claim 1, wherein the process gas consists essentially of Cl₂, O₂, and N₂.

8. The method of claim 1, wherein the flow rate of Cl₂ is from about 20 to about 800 sccm.

9. The method of claim 1, wherein the flow rate of N₂ is from about 4 to about 60 sccm.

10. The method of claim 1, wherein the flow rate of O₂ is from about 0.1 to about 40 sccm.

11. The method of claim 1, wherein in step (b), the plasma is formed by applying a current at a power level of about 200 to 2000 Watts to an inductor coil adjacent to the plasma zone.

12. The method of claim 1, wherein in step (b), the plasma is attracted to the substrate by applying a voltage at a power level of about 5 to 500 Watts to process electrodes in the plasma zone.

13. The method of claim 1, wherein the plasma zone is maintained at a pressure 0.1 to 100 mTorr.

14. A method of etching a substrate comprising metal silicide and polysilicon layers, the method comprising the steps of:

(a) placing the substrate in a process chamber comprising (i) process electrodes therein, and (ii) an inductor coil adjacent to the process chamber;

(b) introducing into the process chamber, process gas comprising Cl₂, O₂, and N₂ ; and

(c) ionizing the process gas to form plasma ions that energetically impinge on the substrate by (i) applying RF current at a first power level to the inductor coil, and (ii) applying a RF voltage at a second power level to the process electrodes,

wherein the volumetric ratio of Cl₂, O₂, and N₂, and a power ratio P_r of the first power level to the second power level are selected so that the metal silicide layer is etched at a first etch rate that is at least 1.2 times higher than a second rate of etching of the polysilicon layer, while providing substantially anisotropic etching of the metal silicide and polysilicon layers.

15. The method of claim 14, wherein the volumetric flow ratio of O₂ :

N₂ is from about 0.25;

1 to about 5;

1.

16. The method of claim 15, wherein the volumetric flow ratio of O₂ :

N₂ is from about 0.5;

1 to about 3;

1.

17. The method of claim 14, wherein the ratio of the volumetric flow of Cl₂ to the combined volumetric flow of O₂ and N₂ is from about 5:

1 to about 20;

1.

18. The method of claim 17, wherein the ratio of the volumetric flow of Cl₂ to the combined volumetric flow of O₂ and N₂ is from about 7:

1 to about 15;

1.

19. The method of claim 14, wherein the power ratio P_r of the first power level to the second power level is from about 0.1:

1 to about 100;

1.

20. The method of claim 14, wherein the first power level is from about 200 to about 2000 Watts.

21. The method of claim 14, wherein the second power level is about 5 to about 500 Watts.

22. A method of etching a substrate surface comprising metal silicide and polysilicon layers, the method comprising the steps of:

(a) placing the substrate surface facing a plasma zone comprising a ceiling having an apex with a height H of about 100 mm to about 175 mm above the substrate surface, the plasma zone having process electrodes and an inductor coil for energizing a plasma; and

(b) energizing a quasi-remote plasma in the plasma zone by introducing into the plasma zone, a process gas comprising Cl₂, O₂, and N₂, and applying RF current at a first power level to the inductor coil and RF voltage at a second power level to the process electrodes,

wherein the volumetric ratio of Cl₂, O₂, and N₂, and the power ratio P_r of the first power level to the second power level are selected to form a quasi-remote plasma for anisotropically etching the metal silicide layer at a first etch rate that is at least 1.2 times higher than a second rate of etching of the polysilicon layer.

23. The method of claim 22 wherein the ratio of the volumetric flow of Cl₂ to the combined volumetric flow of O₂ and N₂ is from about 5:

1 to about 20;

1.

24. The method of claim 23 wherein the volumetric flow ratio of O₂ :

N₂ is from about 0.25;

1 to about 5;

1.

25. The method of claim 22 wherein the process gas consists essentially of Cl₂, O₂, and N₂.

26. The method of claim 25 wherein the plasma zone comprises a volume of about 10,000 to about 50,000 cm³, and wherein the flow rate of Cl₂ is from about 20 to about 800 sccm, the flow rate of N₂ is from about 4 to about 60 sccm, and the flow rate of O₂ is from about 0.1 to about 40 sccm.

27. The method of claim 22 wherein the plasma is energized by applying a current at a power level of about 200 to about 2000 Watts to the inductor coil, and applying a voltage at a power level of about 5 Watts to about 500 Watts to the process electrodes.

28. The method of claim 22 wherein the plasma zone comprises a multi-radius dome ceiling and the quasi-remote plasma is formed between the substrate surface and the dome ceiling to provide a uniform distribution of plasma ions across the substrate surface.