Two step copper electroplating process with anneal for uniform across wafer deposition and void free filling on ruthenium coated wafers

• US 7,964,506 B1
• Filed: 03/06/2008
• Issued: 06/21/2011
• Est. Priority Date: 03/06/2008
• Status: Active Grant

• Current Assignee: Novellus Systems Incorporated (LAM Research Corporation)
• Original Assignee: Novellus Systems Incorporated (LAM Research Corporation)
• Inventors: Mayer, Steve, Sukamto, John, Ponnuswamy, Thomas, Reid, Jonathan
• Primary Examiner(s): Landau; Matthew C
• Assistant Examiner(s): MCCALL SHEPARD, SONYA D
• Application Number:
  US12/075,023
• Time in Patent Office: 1,202 Days
• Field of Search: 438584-688, 438694-703, 257/E21.586
• US Class Current: 438/687
• CPC Class Codes: C25D 17/001 Apparatus specially adapted for electrolytic coating of wafers, e.g. semiconductors or solar cells
• CPC Class Codes: C25D 3/38 of copper
• CPC Class Codes: C25D 5/18 Electroplating using modulated, pulsed or reversing current
• CPC Class Codes: C25D 5/50 by heat-treatment
• CPC Class Codes: C25D 7/123 Semiconductors first coated with a seed layer or a conductive layer
• CPC Class Codes: H01L 21/2885 using an external electrical current, i.e. electro-deposition
• CPC Class Codes: H01L 21/76843 formed in openings in a dielectric
• CPC Class Codes: H01L 21/76864 Thermal treatment
• CPC Class Codes: H01L 21/76873 for electroplating
• CPC Class Codes: H01L 2221/1089 Stacks of seed layers

Abstract

A two-step semiconductor electroplating process deposits copper onto wafers coated with a semi-noble metal in manner that is uniform across the wafer and free of voids after a post electrofill anneal. A seed-layer plating bath nucleates copper uniformly and conformably at a high density in a very thin film using a unique pulsed waveform. The wafer is then annealed before a second bath fills the features. The seed-layer anneal improves adhesion and stability of the semi-noble to copper interface, and the resulting copper interconnect stays void-free after a post electrofill anneal.

Claims

1. A semiconductor processing method for depositing copper comprising:

providing a semiconductor wafer having a semi-noble metal layer thereon;

depositing a seed layer of copper onto the metal layer using an electroplating process with a first electrolyte comprising a copper salt and a copper complexing agent, wherein the resistivity of the first electrolyte is at least about 200 ohms cm, thereby promoting a generally uniform deposition rate across a plating surface of the wafer, and wherein depositing the seed layer comprises applying a current waveform, comprising;

a first step of applying a forward direct current for a first duration,

a second step of alternating forward and reverse current pulses for a second duration, and

a third step of applying a forward direct current for a third duration, wherein substantially all of the copper seed layer is deposited during the third step;

annealing the seed layer; and

depositing a bulk-layer of copper onto the annealed seed layer of copper using an electroplating process employing a second electrolyte.

2. The method of claim 1, wherein the annealing is performed in the presence of forming gas, plasma, or other reducing atmosphere.

3. The method of claim 1, wherein the annealing temperature is about 100 to 400°

C.

4. The method of claim 1, wherein the annealing temperature is about 100 to 200°

C.

5. The method of claim 1, wherein the annealing temperature is about 150°

C.

6. The method of claim 1, wherein the wafer is annealed for a period of between about 10 and 1000 seconds.

7. The method of claim 1, wherein the wafer is annealed for a period of between about 300 and 900 seconds.

8. The method of claim 1, wherein the wafer is annealed for a period of about 120 seconds.

9. The method of claim 1, further comprising:

pretreating the semi-noble metal layer by annealing.

10. The method of claim 1, wherein the resistivity of the first electrolyte is about 1000-2000 ohms cm.

11. The method of claim 1, wherein the complexing agent in the first electrolyte is EDTA, citrate, pyrophosphate, oxalate, triethanolamine, dimercaptosuccinic acid, nitrilotriacetate, dimercaprol, desfuroxamine mesylate or combinations thereof.

12. The method of claim 1, wherein the copper salt is copper citrate, copper pyrophosphate, or copper oxalate.

13. The method of claim 1, wherein the first electrolyte causes a copper plating reaction to occur at a potential of about −

0.8 to −

2.0 volts.

14. The method of claim 1, wherein the first electrolyte causes a copper plating reaction to occur at a potential that is about 200-1000 millivolts more cathodic than would occur in a conventional copper-plating electrolyte.

15. The method of claim 1, wherein the seed layer of copper deposited has a thickness of about 15-60 angstroms.

16. The method of claim 1, wherein the reverse current pulse strips off substantially all of the copper deposited during the forward current pulse of the second step.

17. The method of claim 1, wherein the forward direct current of the first step is between about 0.6-1.0 amps for a period of about 0.5-2 seconds.

18. The method of claim 1, wherein the forward direct current of the third step is between about 0.6-1.0 amps, and the third duration is about 10-22 seconds to deposit a 30-70 angstrom seed layer.

19. The method of claim 1, wherein the semi-noble metal is ruthenium, palladium, rhodium, iridium, osmium, cobalt, or nickel.

20. The method of claim 1, wherein the semi-noble metal layer serves as at least a portion of a diffusion barrier.

21. The method of claim 1, wherein the depositing a seed layer operation is performed in a first electroplating module and the depositing a bulk-layer operation is performed in a second electroplating module.

22. The method of claim 1 wherein the copper salt in the first electrolyte is different from a copper salt of the second electrolyte.

23. The method of claim 16, wherein based on a 300 mm wafer, the forward current pulse of the second step is between about 0.6-0.9 amps for a period of about 700-1500 millisecond;

the reverse current pulse is about 0.2-0.5 amps for a period of about 400-600 millisecond; and

, the second duration is about 8-15 seconds.

24. The method of claim 21, wherein the annealing the seed layer operation is performed in an annealing station in the same semiconductor processing tool as the first and second electroplating modules.

25. A method for depositing a copper seed layer comprising:

providing a semiconductor wafer having a semi-noble metal layer thereon;

applying forward and reverse current pulses to the metal layer using a process with an electrolyte to treat the metal layer and thereby improve copper seed layer nucleation and coverage, wherein the electrolyte comprises a copper salt and a copper complexing agent, wherein the reverse current pulse strips off substantially all of the copper deposited during the forward current pulse; and

depositing the copper seed layer onto the metal layer using an electroplating process with the electrolyte by applying a forward current.

26. The method of claim 25, wherein when applying the forward and reverse current pulses to the metal layer, a first pulse is a forward current pulse.

27. The method of claim 25, wherein when applying the forward and reverse current pulses to the metal layer, a first pulse is a reverse current pulse that treats the metal layer.

28. The method of claim 25, wherein applying the forward and reverse current pulses comprises applying multiple forward and reverse current pulse pairs.

29. The method of claim 25, further comprising:

depositing a bulk-layer of copper onto the copper seed layer using an electroplating process with a second electrolyte.