Effect of UV-wavelength on Hardening Process of Porogen-containing and Porogen-free Ultra-low-k PECVD Glasses A.M. Urbanowicz*, K. Vanstreels, P. Verdonck, E. Van Besien, Ch. Trompoukis, D. Shamiryan, S. De Gendt and M.R. Baklanov *also at Semiconductor Physics Department, Katholieke Universiteit Leuven AVS 2010 17-22 October
Outline Introduction Ultra low-k dielectrics fabricated by PECVD and porogen residue problem New PECVD curing approach: UV-curing of porogen-free films UV-curing as a photochemical process Experimental setup Results Organic residues content in low-k matrix studied by UV-spectrocopic ellipsometry Effect of UV-curing wavelength on mechanical properties of porogen-free films Effect of UV-curing wavelength on dielectric constant of the films Conclusions Adam Urbanowicz, AVS 57th Oct 17-22, 2010, Albuquerque, NM 2
Ultra-low-k PECVD dielectric and porgen residue challange Porogen residue removal degrades mechanical properties of ultra-low-k PECVD k~ 2.5 Prior Art UV curing Film hardening Porogen removal k<2.3 Porogen Porogen residue A. M. Urbanowicz, K. Vanstreels, D. Shamiryan, S. De Gendt and M. Baklanov, Electrochem. Solid State Lett., 12, H292 (2009). 3
Ultra-low-k PECVD dielectric and porgen residue challange Porogen residue degrades electrical properties PECVD (k=2.3) high residue content PECVD (k=2.3)+ H 2 -AFT - no residue PECVD (k=2.5) low residue content PECVD (k=2.5)+ H 2 -AFT no residue E. Van Bensien, L. Zhao, M. Pantouvaki, D. De Roest, I. Ciofi, K. Croes, A. M. Urbanowicz et. al Electrical Evaluation of Low-k Dielectrics with Various Degree of Porosity in Planar Capacitor Structures, in Core Partner Workshop, IMEC, Leuven (2010). 4
New curing technology of PECVD ultra-low-k dielectrics Prior Art UV curing Film hardening Porogen removal New curing technology Gas inlet He/H 2 Plasma area Porogen removal Porogen fully removed? UV curing Skeleton hardening H H H Grid : electrical neutralization Reactive species Porogen Porogen residue Wafer at 280 C A.M. Urbanowicz, K. Vanstreels, P. Verdonck, D. Shamiryan, S. De Gendt and M. Baklanov, J. Appl. Phys., 107 (2010). 5
Goal: Study of the effect of the UV-curing wavelength on porogenfree films >200 nm ~172 nm 0.22 Laws of Photochemistry: Porogen as deposited 0.20 0.18 Only light that is absorbed can be effective in producing photochemical change. (Grotthus-Draper Law: 1817, 1843). One particle is excited for each quantum of radiation (photon) absorbed (Stark-Einstein Law: 1912) Energy of an absorbed photon must be equal to or greater than the weakest bond in the molecules (Bolton) H 2 -AFT 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 extinction coefficient L. Prager, P. Marsik, L. Wennrich, M. R. Baklanov, S. Naumov, L. Pistol, D. Schneider, J. W. Gerlach, P. Verdonck and M. R. Buchmeiser, Microelectronic Engineering, 85, 2094 (2008). S. Eslava, F. Iacopi, A. M. Urbanowicz, C. E. A. Kirschhock, K. Maex, J. A. Martens and M. R. Baklanova, Journal of the Electrochemical Society, 155, G231 (2008). A. M. Urbanowicz, B. Meshman, D. Schneider and M. R. Baklanov, Physica Status Solidi a-applications and Materials Science, 205, 829 (2008). 0.00-0.02 600 500 400 300 200 Si-CH Wavelenght [nm] 3 Photodissotiation threshold 6
Experimental setup setup UV curing (166 s) Deposition of 130 nm films Porogen removal Gas inlet 1 350 s 2a He/H Plasma area 2 NB 172±15 nm Porogen H H H Grid : electrical neutralization Reactive species Wafer at 280 C 2b BB >200 nm Skeleton hardening BB= broad band NB= narrow band 7
Curing of porogen-containing films results in porogen residues generation As deposited UV-cured Porogen residue Porogen residue (a-c) contains sp 2 orbitals (C=C) which have transition band ~4.5 ev (275 nm) UV Spectrocopic Ellipsometry Porogen 1.65 0.22 1.60 as deposited 0.20 0.18 refractive index 1.55 1.50 1.45 1.40 1.35 1.30 as deposited UV ~ 172 nm UV>200 nm UV ~ 172 nm UV>200 nm 0.16 0.14 0.12 0.10 0.08 0.06 0.04 extinction coefficient 0.02 1.25 0.00 1.20 900 750 600 450 300 150 Wavelenght [nm] -0.02 900 750 600 450 300 150 Wavelenght [nm] P. Marsik, P. Verdonck, D. De Roest and M. R. Baklanov, Thin Solid Films, 518, 4266 (2010). 8
Curing of porogen-free films results in porogen-residue-free films As deposited Gas inlet He/H 2 Plasma area Porogen removal Porogen fully removed UV curing Skeleton hardening Grid : electrical neutralization H H H Reactive species Porogen Wafer at 280 C 1.65 0.22 refractive index 1.60 1.55 1.50 1.45 1.40 1.35 1.30 1.25 as deposited UV ~ 172 nm UV>200 nm H 2 -AFT + UV>200 nm H 2 -AFT+ UV ~ 172 nm 1.20 900 750 600 450 300 150 Wavelenght [nm] as deposited UV ~ 172 nm UV>200 nm H 2 -AFT + UV>200 nm 0.20 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 H 2 -AFT+ UV ~ 172 nm -0.02 900 750 600 450 300 150 Wavelenght [nm] extinction coefficient 9
Greater thickness loss after 172 nm NB UV than for >200 nm BB UV Thickness loss (shrinkage), % 18 16 14 12 10 8 6 4 2 H 2 -AFT UV ~ 172 nm UV > 200 nm cured with porogen (conventional) cured without porogen (after H 2 -AFT) 0 Observations: More thickness loss for films without porogen for 172 nm UV curing (improved cross-linking) 10
172 nm UV curing of porgen-free low-k results in greater YM than 200 nm UV Young's Modulus [GPa] 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Nano-indentation and Ellipsometric porosimetry F ilm s c u r e d w ith p o ro g e n 1 7 2 n m U V 2 0 0 n m U V 2 0 2 5 3 0 3 5 4 0 4 5 5 0 O p e n p o r o s ity [% ] F ilm s c u re d w ith o u t p o r o g e n H 2 -AFT 11
Pore radius is greater for 172 nm UV due to more efficient Si-O-Si matrix cross-linkage Ellipsometric porosimetry 25 H2-AF H2-AFT + UV >200 nm H2-AFT + UV ~ 172 nm 20 dv/dr 15 10 micropores 5 0 1.0 1.5 2.0 2.5 3.0 Pore radii [nm] Matrix can be x-linked 12
Improved cross-linkage of Si-O-Si skeleton for ~172 nm UV-cure optimal cross-linking only T-groups T CH 3 FTIR cross-linking with D-groups Methyl Oxygen Silicon Normalized absorbance, a.u. 0.25 0.20 0.15 0.10 0.05 0.00 O Si O O Si-CH 3 H 2 -AFT H 2 -AFT + UV~172 nm H 2 -AFT + UV>200 nm 1300 1290 1280 1270 1260 1250 Wavenumber, cm -1 D O CH 3 Si CH 3 O A.M. Urbanowicz, K. Vanstreels, P. Verdonck, D. Shamiryan, S. De Gendt and M. Baklanov, J. Appl. Phys., 107 (2010). 13
UV-curing of porogen-free films results in its lower k-values k-value 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 cured with porogen (conventional) k at 100 khz (metal dots) k at 4 GHz (near-field probe) cured without porogen (after H 2 -AFT) Observation for porogen free-films: >200 nm UV-curing results in lower k-value than ~172 nm UV 14
Summary: UV-curing wavelength vs achieved characteristics of the porogen-residue-free films IMEC s data base for various organo-silica low-k 3 2.8 k value 3.2 2.6 2.4 2.2 2 UV ~172 nm UV>200 nm Pore size (nm) 100 50 10 5 1 0.5 UV>200 nm UV ~172 nm Elastic modulus (GPa) 50 40 30 20 10 8 5 4 3 2 UV >200 nm UV ~172 nm 1.8 0 10 20 30 40 50 60 Porosity (vol. %) 0.1 1.8 2 2.2 2.4 2.6 2.8 3 k value Green area ITRS requirements 1 1.8 2 2.2 2.4 2.6 2.8 3 k value W. Volksen, D. M. Miller and G. Dubois, Chem. Rev., 110, 56 (2010). K. Maex, M. R. Baklanov, D. Shamiryan, F. Iacopi, S. H. Brongersma and Z. S. Yanovitskaya, J. Appl. Phys., 93, 8793 (2003). 15
Conclusionscuring technology Conclusions UV-curing in the presence of porogen results in: porogen residue generation comparable mechanical properties and k-values for both UV-sources used UV-curing after porogen removal with H 2 -AFT results in: narrow band (~172 nm) YM of 6.64±0.61 GPa k of 2.2±0.01 broad band (<200 nm) YM of 3.85±0.38 GPa k of 2.0±0.01 16
Future planscuring technology Conclusions Optimization of porogen residue-free ultra low-k PECVD films different UV-cure times combined narrow-band and broadband UV-curing Electrical evaluation of achieved films using planar capacitor structures CMP tests of porogen-residue-free films 17