Barrier Layers Technology

1. Barrier Layers Technology Prof. Yosi Shacham-Diamand Department of Physical Electronics Tel-Aviv University, Tel-Aviv 69978 ISRAEL AMC2000

2. Outline • Introduction • Copper Interconnect technology • Barrier layers - overview • Process development and integration • Barrier layers modeling • Barrier analysis, testing & monitoring • Summary AMC2000

3. Introduction • Structure of Microchips • ULSI metallization technology • Metallization roadmap • Downscaling issues • Performance issues • Manufacturing issues • Where is the bottom ? AMC2000

4. Copper multi-level metallization AMC2000

5. IBM CMOS 7S process AMC2000

6. Copper chips... • IBM power PC 750 • Mitsubishi Electric eRAMTM family • AMD K7(Athalon) • UMC 0.18 mm process • Motorola 333MHz SRAM • Lucent & Chartered 0.16 mm process AMC2000

7. IBM PowerPC 750 AMC2000

8. Interconnect network - 6-7 layers of metallization Silicon substrate (600-800 mm) Active devices layer ( 1-2 mm) Structure of microchips AMC2000

9. ULSI metallization technology אינטל 2000 AMC2000

10. Gate and Interconnect delays AMC2000

11. Delay modeling - the barrier effect • The specific resistance (rb ) of the barrier layers is higher than that of the Cu, (rCu) W H Without barrier: L: line length With barrier (tb: barrier thickness) AMC2000 Assumption: complete barrier coating

12. Cu Damascene interconnect resistivity AMC2000

13. Effect of the barrier layer on the interconnect delay Interconnect delay Tint ~ Rint*Cint - including the barrier. In the case of a Damascene technology: For rb >> rCu we get the the interconnect delay increases as the ratio between the actual copper line cross section and the total cross section. AMC2000

14. Barrier layers - overview Why do we need barriers ? Requirements from barriers AMC2000

15. Barrier layers for Cu metallization • Why do we need barrier layers? • Copper affects Si properties • Cu affects SiO2 properties • Cu affect most insulators properties • Cu adheres poorly to bottom and side ILD • Why do we need a top barrier (capping layer) • Cu corrodes • Cu adheres poorly to top ILD AMC2000

16. Requirements from barrier layers • Step coverage on high aspect ratio holes and trenches • Low thin film resistivity • Adhesion to the ILD • Adhesion to Cu • Stable at all process temperatures • Process compatible to the ILD • Process compatible to CMP • Act as a good barrier AMC2000

17. Barrier layers - types • Sacrificial • Stuffed - impurities in the grain boundaries • Amorphous - no grain boundaries AMC2000

18. Diffusion barrier - classification of the candidates for barriers that has been investigated in the last 15 years • transition metals • transition metal alloys • transition metal - silicon • transition metal nitrides, oxides, or borides • Miscellaneous: ternary alloys, a-carbon, etc. AMC2000

19. Summary of barrier layer classification • Transition metals fail as barrier at lower temperatures than their nitrides • transition metal silicides fail due to the reaction of the Si with the Cu. The reaction is most likely to happen at the grain boundaries • Amorphous barriers offer very high reaction temperatures, however, they have very high specific resistivity • The barrier properties depend also on the deposition method. AMC2000

20. Process development and manufacturing considerations AMC2000

21. Step coverage issues Barrier layer too thick Barrier layer too thin AMC2000

22. Coverage issues • Nonuniform sidewall deposition: • agglomeration • Bad coverage at the bottom corner - can be amplified if the bottom corner has some overetch of the layer below AMC2000

23. The effect of pre-deposition clean on the barrier integrity Physical process in Ar+ ions Reactive clean • Problems • Damage to the barrier • Damage to the dielectric • Barrier metal and Cu • Sputtering and re-deposition on the sidewalls AMC2000

24. Copper patterning • Dry etch • Difficult, expensive • Conventional equipment • Dual Damascene • Fully planar, lower cost, • New technology AMC2000

25. Cu process options AMC2000

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28. Electroplating solutions • Cu ions - Cu sulfate • Acid - H2 SO4 for pH adjustment • HCl - Affects Cu surface adsorption; Halide ad-layer drives Cu growth. It also acts as a surfactant and stabilizes grain growth. Cu deposition is driven by the desorption of the halides. AMC2000

29. Electroplating Based Process Sequence Pre-clean IMP barrier + Copper Electroplating CMP 25 nm 10-20 nm + 100-200 nm Simple, Low-cost, Hybrid, Robust Fill Solution AMC2000

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32. Diffusion barrier for Copper (I) • PVD Ta,TiN, and TaN • Neutrals sputtering • Collimated & Non collimated • Ions sputtering • RF ionized • HCM- Hollow Cathode Magnetron • CVD of TiN • Iodine or Chlorine based chemistry • CVD of Ta and TaN (or both) • Bromide based chemistry • MOCVD of TiN • TDMAT & TDEAT AMC2000

33. Target Target Target Substrate Substrate Substrate Bias DC magnetron sputtering Collimated sputtering IMP - Ionized Metal Plasma PVD barrier technologies RF AMC2000

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35. Diffusion barrier comparison, (M. Mossavi et al., IITC 98) AMC2000

36. Vias with IMP TaN AMC2000

37. Sputtered WxN barrier AMC2000

38. MOCVD TiN Precursors:Tetrakis-dimethylamino Titanium AMC2000

39. Other Novel barriers RuO2 r=40-250 mW cm TaSiN,TiSiN r=200-600 mW cm WBN r=300-10000 mW cm CoWP r=20-120 mW cm AMC2000

40. Electroless barriers Surface activation methods AMC2000

41. Advantage of Electroless barriers • Conformal • Low cost • Good quality - low r, low stress • can be integrated with electroless copper Barrier Cu ILD AMC2000

42. Co(W,P) barrier layer AMC2000

43. Specific resistivity vs. solution composition AMC2000

44. Barrier layers modeling • Diffusion models - kinetics • Reaction models - thermodynamics AMC2000

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46. Equilibrium thermodynamics of diffusion barriers (C.E. Ramberg et al., Microelectronics Microengineering, 50 (2000) 357-368) • Cu makes silicides with silicon • Barriers include transition metal+metaloid (Si,B,or N) AMC2000

47. N TiN Ti2N Cu Cu4Ti Cu4Ti3 CuTi CuTi2 Ternary phase diagrams • The lack of Ta-Cu compounds yield a broad range of compositions in equilibrium with Cu. • Ti-rich compositions are expected to react with Cu N TaN Ta2N Ti Cu Ta AMC2000

48. Barrier Analysis & monitoring • Materials science techniques: • AES, SIMS, RBS, SEM • Electrical characterization: • I-V • C-V & C-t AMC2000

49. Electrical characterization: MOS capacitors Capacitance measurements: CV: Flat band voltage, interface states Ct : minority carrier lifetime, surface recombination velocity IV &It: metal/insulator integrity. AMC2000

50. Ideal MOS capacitance-voltage curve. Solid curve - High f , Dotted curve Low frequencies. Oxide thickness is 140. NA = 1·1015 cm-3. Low frequency High frequency Relaxation High frequency - fast sweep AMC2000