Process for etching tungsten silicide overlying polysilicon particularly in a flash memory

• US 7,754,610 B2
• Filed: 06/02/2006
• Issued: 07/13/2010
• Est. Priority Date: 06/02/2006
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Deshmukh, Shashank C., Lee, Kyeong-Tae, Yu, Jae Bum, Choi, Jinhan, Lill, Thorsten B., Jang, Bi, Shen, Meihua
• Primary Examiner(s): OLSEN, ALLAN W
• Application Number:
  US11/445,709
• Publication Number:
  US 20070281477A1
• Time in Patent Office: 1,502 Days
• Field of Search: 216/68, 216/71, 216/75, 216/79, 438/719, 438/721, 438/734
• US Class Current: 438/689
• CPC Class Codes: H01L 21/32136 using plasmas
• CPC Class Codes: H01L 21/32137 of silicon-containing layers
• CPC Class Codes: H01L 29/40114 the electrodes comprising a conductor-insulator-conductor-insulator-semiconductor structure

Abstract

A method of plasma etching tungsten silicide over polysilicon particularly useful in fabricating flash memory having both a densely packed area and an open (iso) area requiring a long over etch due to microloading. Wafer biasing is decreased in the over etch. The principal etchant include NF₃ and Cl₂. Argon is added to prevent undercutting at the dense/iso interface. Oxygen and nitrogen oxidize any exposed silicon to increase etch selectivity and straightens the etch profile. SiCl₄ may be added for additional selectivity.

Claims

1. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:

placing onto an electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon;

a first step of flowing into the chamber a first gas mixture comprising an etching gas comprising NF₃ and Cl₂ and an oxidizing gas comprising oxygen gas and nitrogen gas;

biasing the electrode with a first level of RF power;

applying a second level of RF power to excite the first gas mixture into a first plasma to thereby etch at least the tungsten-containing layer sufficiently that at least some of the silicon layer is exposed;

a subsequent second step of flowing into the chamber a second gas mixture comprising the etching gas having a smaller fraction of NF₃ than in the first step and the oxidizing gas having a larger fraction of nitrogen gas than in the first step;

biasing the electrode with a third level of RF power greater than the first level; and

applying a fourth level of RF power to excite the second gas mixture into a second plasma to thereby etch possibly remaining portions of the tungsten-containing layer remaining before the second gas mixture had been excited into the second plasma.

2. The method of claim 1, wherein the first step further comprises flowing a noble gas selected from the group consisting of helium and argon into the chamber.

3. The method of claim 1, wherein a ratio of the nitrogen gas to the oxygen gas is at least 4.

4. The method of claim 1, wherein a ratio of the fourth level to the third level of RF powers is between 4 and 8.

5. The method of claim 1, further comprising the steps of:

a subsequent third step of flowing a third gas mixture into the chamber comprising the etching gas and the oxidizing gas, wherein a ratio of the nitrogen gas to the oxygen gas is greater than in the second step;

biasing the electrode with a fifth level of RF power less than the third level; and

applying a sixth level of RF power to excite the third gas into a plasma.

6. The method of claim 1, wherein the first gas mixture additionally comprises a passivating gas comprising silicon and chlorine constituents.

7. The method of claim 1, wherein the tungsten-containing layer and the silicon layer are included in a flash memory structure including an ONO layer comprising a first oxide layer, a nitride layer, and a second oxide layer overlying a gate structure formed in a silicon substrate.

8. The method of claim 1, wherein a ratio of the second level to the first level is between 4 and 8.

9. The method of claim 1, wherein the second gas mixture additionally comprises a passivating gas comprising silicon and chlorine constituents.

10. The method of claim 9, wherein the passivating gas comprises silicon tetrachloride.

11. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:

placing onto an electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon;

a first step of flowing into the chamber a first gas mixture comprising an etching gas comprising chorine and fluorine, an oxidizing gas comprising oxygen gas and nitrogen gas, and a passivating gas comprising silicon tetrachloride;

biasing the electrode with a first level of RF power;

applying a second level of RF power to excite the first gas mixture into a plasma to thereby selectively etch relative to the silicon layer at least the tungsten-containing layer sufficiently that at least some of the silicon layer is exposed.

12. The method of claim 11, wherein a ratio of the second level to the first level is between 4 and 8.

13. A method of etching a tungsten-containing layer comprising tungsten and silicon and overlying a silicon layer, comprising the steps of:

placing within a plasma reaction chamber a substrate containing the tungsten-containing layer;

flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising a chlorine- and fluorine-containing gas and a passivating gas comprising a silo-chloro compound; and

exciting the first gas mixture into a plasma to thereby etch the tungsten-containing layer selectively to the silicon layer.

14. The method of claim 13, wherein the silo-chloro compound comprises silicon tetrachloride.

15. The method of claim 13, wherein the chlorine- and fluorine-containing gas comprises nitrogen trifluoride and chlorine gas.

16. The method of claim 13, wherein the first gas mixture further includes a gas chosen from the group consisting of oxygen gas and nitrogen gas.

17. The method of claim 13, wherein the exciting step includes applying RF power to an inductive coil associated with the chamber and further including supplying RF power through a capacitive coupling circuit to an electrode supporting the substrate.

18. A multi-step method of etching tungsten silicide over silicon, comprising the steps of:

placing a substrate containing a tungsten silicide layer overlying a silicon layer onto an electrode in a plasma reaction chamber;

a first flowing step of flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising nitrogen trifluoride and chlorine gas, an oxidizing gas comprising oxygen gas and nitrogen gas, and argon;

a first exciting step of exciting the first gas mixture into a first plasma to etch through the tungsten silicide layer in at least a portion of the substrate while biasing the electrode with a first level of RF power;

a second flowing step of flowing into the plasma reaction chamber a second gas mixture comprising the etching gas and the oxidizing gas while biasing the electrode with a second level of RF power lower than the first level; and

a second exciting step of exciting the second gas mixture into a second plasma while biasing the electrode with a second level of RF power lower than the first level to etch possibly remaining portions of the tungsten silicide layer remaining at the conclusion of the first flowing step.

19. The method of claim 18, wherein less nitrogen trifluoride is flowed into the chamber in the second step than in the first step.

20. A method of etching a tungsten silicide layer, comprising the steps of:

placing within a plasma reaction chamber a substrate containing a tungsten silicide layer;

flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising a chlorine- and fluorine-containing gas and a passivating gas comprising constituents including silicon and chlorine; and

exciting the first gas mixture into a plasma to thereby etch the tungsten silicide layer.

21. The method of claim 20, wherein the passivating gas comprises silicon tetrachloride.

22. The method of claim 20, wherein the etching gas comprises nitrogen trifluoride and chlorine gas.

23. The method of claim 20, wherein the first gas mixture further includes a gas chosen from the group consisting of oxygen gas and nitrogen gas.

24. The method of claim 20, wherein the exciting step includes applying RF power to an inductive coil associated with the chamber and further including supplying RF power through a capacitive coupling circuit to a pedestal electrode supporting the substrate.

25. A multi-step method of etching tungsten silicide over silicon, comprising the steps of:

placing a substrate containing a tungsten silicide layer of tungsten overlying a silicon layer onto a pedestal electrode in a plasma reaction chamber;

a first step of flowing into the plasma reaction chamber a first gas mixture comprising an etching gas comprising nitrogen trifluoride and chlorine gas, a first gas comprising oxygen gas and nitrogen gas, and argon;

exciting the first gas mixture into a first plasma to etch through the tungsten silicide layer in at least a portion of the substrate while biasing the pedestal electrode with a first level of RF power;

a subsequent second step of flowing into the plasma reaction chamber a second gas mixture comprising the etching gas, the first gas, and a passivating gas comprising constituents including silicon and chlorine and exciting the second gas mixture into a second plasma while biasing the pedestal electrode with a second level of RF power greater than the first level to thereby etch possibly remaining portions of the tungsten silicide layer remaining before the second gas mixture had been excited into the second plasma.

26. The method of claim 25, wherein the step of exciting the first gas mixture includes applying RF power to an inductive coil associated with the chamber.

27. The method of claim 25, wherein the passivating gas comprises silicon tetrachloride.

28. A method of etching a tungsten-containing layer overlying a silicon layer, comprising the steps of:

placing onto a pedestal electrode in a plasma reaction chamber a substrate containing the tungsten-containing layer, the silicon layer, and an etching mask overlying the tungsten-containing layer, wherein the silicon layer consists principally of silicon;

a first step of flowing into the chamber a first gas mixture comprising a first gas comprising chlorine and NF₃ and a second gas comprising oxygen gas and nitrogen gas;

biasing the pedestal electrode with a first level of RF power;

applying a second level of RF power to excite the first gas mixture into a first plasma to thereby etch at least the tungsten-containing layer sufficiently that at least some of the silicon layer is exposed, wherein a ratio of the second level to the first level is between 4 and 8;

a subsequent second step of flowing into the chamber a second gas mixture comprising the first gas having a smaller fraction of NF₃ than in the first step, the second gas having a larger fraction of nitrogen gas than in the first step, and a passivating gas comprising silicon and chlorine constituents;

biasing the pedestal electrode with a third level of RF power greater than the first level; and

applying a fourth level of RF power to excite the second gas mixture into a second plasma to thereby etch possibly remaining portions of the tungsten-containing layer remaining before the second gas mixture had been excited into the second plasma.

29. The method of claim 28, wherein the passivating gas comprises silicon tetrachloride.

30. The method of claim 28, wherein the first step further comprises flowing a noble gas selected from the group consisting of helium and argon into the chamber.

31. The method of claim 28, wherein a ratio of the nitrogen gas to the oxygen gas in the first step is at least 4.

32. The method of claim 28, wherein the second level of RF power is applied to an inductive coil associated with the chamber.

33. The method of claim 28, wherein a ratio of the fourth level to the third level of RF powers is between 4 and 8.

34. The method of claim 28, further comprising the steps of:

a subsequent third step of flowing a third gas mixture into the chamber comprising the first gas and the second gas, wherein a ratio of the nitrogen gas to the oxygen gas is greater in the third step than in the second step;

biasing the pedestal electrode with a fifth level of RF power less than the third level; and

applying a sixth level of RF power to excite the third gas mixture into a plasma.

35. The method of claim 28, wherein during the second step the plasma of the second gas mixture acts on exposed portions of the silicon layer and etches any remaining portions of the tungsten-containing layer.