1. Copper Electrodeposition on Diffusion Barrier Films- A literature review by Batric Pesic 209 th ECS Meeting-Denver, CO May 07-12, 2006 J1-Electrochemical Processing in ULSI and MEMS II Electrodeposition University of Idaho Department of Materials Science and Engineering Moscow, ID 83844-3024

2. ACKNOWLEDGMENT This work was supported by Micron Technology Foundation under grant MF134

3. INTRODUCTION  Barrier Materials Physical and Chemical Properties  Electrochemical Deposition Methods Electroless - Soluble reducing agent - Insoluble reducing agent Electrodeposition - Direct plating on a barrier film - Direct plating on a seed layer  Some chemistry  My research plans - Techniques - Plating systems

4. J.A. Cunningham, Solid State Technology, June 18, 2003

5. Copper Diffusion Barrier Types According to: J.A. Cunningham, Solid State Technology June 18, 2003 Adhesion increases Resistance to diffusion increases

9. IDEAL DIFFUSION BARRIER REQUIREMENTS 1.Electronically conductive 2.Should not react with Cu, Si and dielectric materials 3.Should have an amorphous microstructure

10. C.E. Ramberg et al., Microelectronics Engineering 50 (2000) 357-368

14. No Si 3 N 4 No Cu-Ta Stable and unstable Cu-Ti alloys Si 3 N 4 everywhere C.E. Ramberg et al., Microelectronics Engineering 50 (2000) 357-368

15. What is better to use, crystalline or amorphous Ta-N? The answer: not consistent 1. MATERIALS SELECTION ISSUE The answer is almost clear: Ta, Ta-N 2. MICROSTRUCTURE ISSUE

16. Amorphous TaN x film is more appropriate to use than crystalline TaN according to: C.-C. Chang, J.S. Chen, and W.-S. Hsu, Failure mechanism of amorphous and crystalline Ta-N films in the Cu/Ta-N/Ta/SiO2 structure J. Electrochemical Society, 151 (11) G746-G750 (2004). No Cu reaction products When amorphous TaNx film at interlayer W.-F. Wu, K.-L. Ou, C.-P. Chou, C.-C. Wu Effects of nitrogen plasma treatment on Ta Diffusion barriers in copper metallization, J. Electrochemical Society, 150 (2) G83-G89, (2003)

17. Crystalline structure of TaN outperforms amorphous TaN according to: G.S. Chen and S.C. Huang, Intrinsic properties and barrier behaviors of thin Films of sputter-deposited single-layered and alternatively layered tantallum Nitrides (Ta2N/TaN), J. Electrochem. Soc., 148(8) G424-429 (2001) Amorphous Ta 2 N: no Cu at 700 o C Crystalline TaN: no Cu at 800 o C Alternate Ta 2 N/TaN: Cu still present at 800 o C Reason for amorphous film deterioration: crystallization grain growth of a-Ta 2 N. Si Ta 2 N CuSi TaN CuSiTa 2 N/TaN/Ta 2 N/TaNCu

18. S. Tsukimoto, M. Moriyama, M. Murakami, Microstructure of amorphous tantalum nitride thin films, Thin Solid Films 460 (2004) 222-226 Amorphous films develop low density columnar boundaries as pathway for Cu diffusion  Crystalline TaN is more efficient

19. ELECTROMIGRATION Two interesting points: 1.Electromigration and stress migration are caused by impurities (H, F, O) introduced during processing T.C. Wang, J. Electrochem. Soc. 152(1) G45-G49 (2005) 2. Direction of current flow plays an important role Gan et al. Effect of current direction on the lifetime of Different levels of Cu dual-damascene metallization Appl. Phys. Letters, 79 (27) (2001) 4592-4594

20. RESISTIVITY Resistivity = f(grain size) Grain size = f(stress) Low stress copper can be deposited only on low stress substrate (seed layer) TaN Ta/TaN TaSiN TaN TaSiN Ta/TaNTaSiN Ta/TaN Balakumar et al. Electrochemical and Solid-State Letters 7(4) G68-71 (2004) T. Hara and K. Namiki Electrochemical and Solid State Letters, 7(5) C57-C60 (2004)

21. ADHESION T. Hara and K. Sakata, Electrochemical and Solid State Letters, 4(10) G77-G79 (2001) T. Hara et al. Electrochemical and Solid State Letters, 7(2) G28-G30 (2004) Adhesion = f(stress, orientation)

22. CHEMISTRY Direct Electrodeposition Electroless Deposition 1.Main purpose to form a Cu seed layer  Fill by electrodeposition Catalyst required (Pd is the best) 2. Complete fill by electroless a) by solution reductant b) by contact displacement Preferred approach Not developed yet Main problem: insulating oxide layer

23. Direct Electrodeposition Ta A. Radisic, G. Oskam, P.C. Searson, J. Electrochem Soc 151 (6) C369-C374 ((2004) S.B. Emery, J.L. Hubbley, D. Roy, J. Elecroanal Chem 568 (2004) 121-133 TaN S. Kim and D.J. Duquette, Electrochem and Solid State Letters 9(2) C38-C40 (2006) Radisic, et al. J. Electrochem Soc 150 (5) C362-367 (2003) TiN S. Kim and D.J. Duquette, J. Electrochem Soc 153(6) C417-C421 (2006) J.J. Kim, S.-K. Y.S.Kim J. Electrochem Soc (151 (1) C97-C101 (2004) (Pd only; no Cu seed) L. Magagnin et al. Microelectronic Engineering 76(2004) 131-136 L. Graham, C. Steinbruchel, D.J. Duquette, J. Electrochem Soc 149 (8) C390-C395 (2002) A. Radisic, et al. J. Electrochem Soc 148 (1) C41-C46 (2001) G. Oskam, P.M. Vereecken, P.C. Searson, J. Electrochem Soc 146(4) 1436-1441 (1999) W C. Wang et al. Thin Solid Films 445 72-79 (2003) C. Wang et al. Electrochem and Solid-State Lett 5(9) C82-C84 (2002

24. CuSO4 HBF 4 Citrate EDTA TaNPt Ta Radisic, et al. J. Electrochem Soc 150 (5) C362-367 (2003) A. Radisic, G. Oskam, P.C. Searson J. Electrochem Soc 151 (6) C369-C374 ((2004) ROLE of OXIDE LAYER

25. CV of Cu 2+ on Ta in 0.1M NaNO 3 +0.6mM Cu(NO 3 ) 2 S.B. Emery et al. J. Electroanalytical Chemistry 568 (2004) 121-133 Two cross-over potentials Cross-over potential function of vertex potential No anodic current Explanation for no anodic current: “…oxide species of Ta act to induce irreversible lattice incorporation or alloying of the deposited Cu…”

26. H.K. Chang et al. Influence of Ti oxide films on Cu nucleation during electrodeposition Materials Science and Engineering A 409 (2005) 317-328

27. H.K. Chang et al. Influence of Ti oxide films on Cu nucleation during electrodeposition Materials Science and Engineering A 409 (2005) 317-328 “Pipe tunneling” along a dislocation core mechanism for copper nucleation

28. IBM Research  1997 First working microprocessor using copper electroplating is fabricated  1998 P.C. Andricacos, C. Uzoh, J.O. Dukovic, J. Horkans, H. Deligianni Damascene copper electroplating for chip inteconnections IBM Research, Vol 42 No 5 (1998) p. 567 - Introduced shape-induced concentration-field effects concept to describe additive distribution within micron size voids during electrodeposition - New terminology: subconformal, conformal and superconformal (superfilling) modes of electrodeposition  2005 P.M. Vereecken, R.A. Binstead, H. Deligianni, P.C. Andriacacos The chemistry of additives in damascene plating, IBM J. Res.&Dev. Vol. 49. No. 1 January 2005  2005 T.P. Moffat, D. Wheeler, M.D. Edelstein, D. Josell, Superconformal film growth: Mechanism and quantification, IBM J. Res.&Dev. Vol. 49. No. 1 January 2005

29. SUPERCONFORMAL FILM GROWTH: Mechanism and quantification T.P. Moffat, W. Wheeler, M.D. Edelstein, D. Josell, IBM J. Res. &Dev. Vol. 49 No. 1 (2005)

30. P.M. Vereecken, R.A. Binstead, H. Deligianni, P.C. Andriacacos, The chemistry of additives in damascene plating, IBM J. Res.&Dev. Vol. 49. No. 1 January 2005

31. Ic: Cu(H 2 O) 6 2+ + e = Cu(H 2 O) 4 + IIc: Cu(H 2 O) 6 2+ + 2e = Cu 0 + 6H 2 O IIa: Cu 0 + 6H 2 O = Cu(H 2 O) 6 2+ + 2e Ia: Cu(H 2 O) 4 + + 2 H 2 O = Cu(H 2 O) 6 2+ + e Cu 0 + Cu(H 2 O) 6 2+ = 2Cu(H 2 O) 4 + + 2H 2 O

32. OTHER APPROACHES Electrodeposition must be in kinetic control regime in order to ensure good quality copper. In order to increase the convection, i.e. to avoid diffusion control, various new interesting studies are appearing: Effect of gravitational strength: M. Morisue et al. J. Electronal Chem 559 (2003) 155-163 Centrifugal fields: A. Eftekhari, Microelectronic Engineering 69 (2003) 17-25 Magnetic fields: M. Uhlemann et al. J Electrochem Soc 151 (9) C598-C603 (2004) M. Uhlemann et al. J Electrochem Soc 152 (12) C817-C826 (2005) Microwave effects: U.K. Sur et al. New J. Chem., 28, 1544-1549 (2004) For fundamental studies, addition of scanning electrochemical microscopy can prove to become an invaluable mechanistic tool.

33. CONCLUSIONS Damascene copper plating is becoming a mature technology. Both, the technology development and the explanation of reaction mechanisms have already been provided by the IBM researchers. Additional research only confirms what has already been postulated, i.e. at most adds some marginal knowledge. More research (chemistry) is needed in the area of direct copper plating on diffusion barriers to avoid a processing step for formation of a seed layer. More research is needed toward development of more efficient barriers. Among the experimental techniques SECM can contribute substantially to understand the phenomena within vias and trenches. By comparing the published literature with the technology status of chip manufacturers there is a feeling that the industry is “ahead of the curve” and that the published research only confirms what the industry already knows.