4 26 Silver Interconnect Technology Intel 22 Fin FET 10 10 Abstract In view of commercial electronic product requirements, the integration circuit (IC) manufacturing technology needs to keep moving to fulfill multiple purposes. Not only the architecture of device changes from planar 2D to 3D for high speed, low power operation but also the breakthrough of functional materials in special process provides higher feasibility in device performance enhancement. In past decade, better performance was achieved using copper in place of aluminum. We wonder that Cu
NANO COMMUNICATION 20 No.1 27 will be still suitable for next 10 years or be replaced by another new material, like silver, carbon nanotube, graphene or photonic interconnect technology. In this paper, we will introduce the challenges of Cu when scaling and the potential for silver in interconnect application. Keywords Interconnect Copper Silver Electromigration Thermal Diffusion 1997 IBM Cu 10 10 Damascene Ta TaN Low k Dielectric Electro-chemical Deposition, ECD Chemical-mechanicalpolishing, CMP 1 ITRS [1] 2018 30 15 2 1.3 Damascene 15 193 Double Patterning 1 Spacer Defined Overlay Error Re-work EUV E-beam Throughput 193 14 90% EUV 60% EUV EUV 2014 EUV EUV 1 [1] Year of Production 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Metal 1 wiring pitch (nm) 76 64 54 48 42 38 34 30 27 24 Metal 1 wining half-pitch (nm) [Based on Hans update (row above)] 38 32 27 24 21 19 17 15 13 12 Metal 1 A/R (for Cu) 1.80 1.80 1.90 1.90 1.90 2.00 2.00 2.00 2.00 2.00 Barrier/cladding thickness (for Cu Metal 1 wiring) (nm)[3] 2.9 2.6 2.4 2.1 1.9 1.7 1.5 1.3 1.2 1.1
4 28 1 2 Profile PVD TaN\Ta PVD 5 [2] 10 PVD [3] 3 微縮化 3
NANO COMMUNICATION 20 No.1 29 TaN\Ta Atomic Layer Deposition, ALD Ru Self-form MnO x MnSiO x 2 1.59 µω-cm 1085 962 PVD CVD [4] 4 SiO 2 TaN Cu Ta 4 2 Properties/Metal Cu Ag Au Al W Resistivity (µω-cm) 1.67 1.59 2.35 2.66 5.65 Melting point ( o C) 1,085 962 1,064 660 3,387 Thermal conductivity (W cm -1 ) 3.98 4.25 3.15 2.36 1.74 Corrosion in Air Poor Poor Excellent Good Good Adhesion with SiO 2 Poor Poor Poor Good Poor Dry etch process No No No Yes Yes Diffustivity in Si (cm 2 /s) (at 400 o C) 2.3 X10-3 e -1.6/KT 1.39 X 10-9 4.2 X 10-2 e -1.0/KT 2.46 X 10-15 Ag < Au < Cu Al < Ag Process (dry) CVD/PVD/ALD CVD/PVD/ALD CVD/PVD/ALD CVD/PVD/ALD CVD/PVD/ALD Process (wet) ECD/E-less ECD/E-less
4 30 4 Cu Si Cu IC IBM IMEC Tungsten Plug ~2 5 CVD-Ru >5 ~10 Ru PVD Overhang e-gun Process Window 35 5 [5] 5 µm TaN\Ta Cu Ru Channel 10 6 Ag/Ti/Si (a) (b) 500 (c) 700
NANO COMMUNICATION 20 No.1 31 [6] 7 TiN Ti TiN TaN TiW [7] 6 Ti 500 200 (b) 700 (c) Ti 5 TiN 550 10 25 450 Thermal Budget 12 TiN 600 3 SiO 2 TiW [8] TiW 600 {111} 8 100 TaN x-ray [9] TaN 650 {111} TaN TaN TiW TaN TiW PVD 7 Ag/TiN/Si TiN 20 ALD ALD Markku Leskela 2007 2011 ALD Precursor ALD-Ag [10,11] 20 6 8 µωcm Bulk = 8 Ag/TaN X-ray 1.59 µω-cm
4 32 3 Ag SiO 2 TiW Sample Orientation As-dep 400 o C 600 o C Random 50.26 35.58 26.06 Ag/SiO 2 {200} + {511} 19.34 25.28 24.28 {111} 30.40 37.5 49.66 Random 51.13 24.12 17.58 Ag/W-Ti {200} + {511} 2.23 17.64 22.10 {111} 46.64 58.24 60.32 Grain Boundary InterfaceScattering ALD 2002 M. Hauder 2005 R. Emling [12,13] 70 2 9 50 4.5 µω-cm 5.25 µω-cm 10 2 4 20% R. Emling 20% 4.2 µω-cm Si [1] ITRS, 2011 [2] C. Zhao et al., Failure Mechanisms of PVD Ta and ALD TaN Barrier Layers for Cu Contact Applications, Microelectronic Engineering, v.84, pp. 2669-2674, 2007. [3] Mike Mayberry, Peering through the Technology Scaling Fog, Symp. of VLSI, 2011. [4] M. Hauder et al., Scaling Properties and Electromigration Resistance of Sputtered Ag Metallization lines, Appl. Phys. Lett., v.78, pp. 838-840, 2001. [5] B. S. Haran et al., 22 nm Technology Compatible Fully Functional 0.1 µm 2 6T-SRAM Cell, Proc. of IEDM, 2008. [6] O. Akhavan et al., Thickness Dependence on Thermal Stability of Sputtered Ag Nanolayer on Ti/Si(100), Applied Surface Science, v.254, pp. 548-551, 2007. [7] L. Gao et al., Thermal Stability of Titanium Nitride Diffusion Barrier Flms for Advanced Silver Interconnects, Microelectronic Engineering, v.76, pp. 76-81, 2004.
NANO COMMUNICATION 20 No.1 33 [8] S. K. Bhagat et al., Texture Formation in Ag Thin Flms: Effect of W-Ti Diffusion Barriers, J. Appl. Phys., v.104, pp. 103534, 2008. [9] Daniel Adams et al., Effectiveness of Reactive Sputterdeposited Ta-N films as Diffusion Barriers for Ag Metallization, J. Vac. Sci. Technol. B 22(5), pp. 2345-2352, 2004. [10] Antti Niskanen et al., Radical-Enhanced Atomic Layer Deposition of Silver Thin Films Using Phosphine- Adducted Silver Carboxylates, Chem. Vap. Deposition, v.13, pp. 408-413, 2007. [11] Maarit Kariniemi et al., Plasma-Enhanced Atomic Layer Deposition of Silver Thin Films, Chem. Mater., v.23, pp. 2901-2907, 2011. [12] M. Hauder et al., Chemical mechanical polishing of silver damascene structures, Microelectronic Engineering, v.64, pp. 73-79, 2002. [13] R. Emling et al., Deposition and CMP of Sub 100 nm Silver Damascene Lines, Microelectronic Engineering, v82, pp. 273-276, 2005.