In this thesis, the impact of high-temperature porogens, their loadings on the moisture uptake and diffusion behavior was investigated for low-k films based on Solid-FirstTM approach. Specifically, di-block and tri-block copolymers such as PS-P4VP and PS-PB-PS were employed as the high temperature porogens, whose decomposition temperature was higher than 300 oC. Three low-k dielectric systems were comprehensively studied in this thesis, namely: (1) MSQ films cured at different temperatures, (2) MSQ/porogens hybrid films with various porogen loadings, cured at 250 oC, which simulated the starting ILD materials in the Solid-FirstTM scheme, and (3) porous films after porogens were completely removed by burn-out at 400oC, which simulated the final porous low-k materials after the completion of Solid-FirstTM integration scheme of Cu/low-k interconnect. The moisture uptake of low-k films was investigated by using a home-built quartz crystal microbalance (QCM).
The moisture uptake of porous MSQ increased from 0.51 % to 1.77 % with raising porosity up to 29 %. The increased moisture absorption could be attributed to (1) increased surface area and (2) increased Si-OH sites on the pore surface due to increased surface area and increased polarity such as Si-OH on the pore surface due to incomplete crosslinking caused by the steric hindrance effect of porogen. High surface area could provide more sites for adsorbents [66], while high concentration of Si-OH could form hydrogen bonding with H2O and even induce multilayered adsorbents through Van der Waals force. Moreover, the deviation of moisture uptake at 30% porogen loading from linearity was presumably caused by a change of pore morphology and/or increased Si-OH at higher degree, which required more in the future.
For MSQ/PS-b-P4VP hybrid low-k films cured at 250 oC, which could be used as the starting ILD for copper damascene process, the moisture adsorption were much larger than their corresponding porous MSQ. In addition, the deviation from ideal mixing rule increased with increasing porogen loading. Several factors contributed to such high moisture uptake; namely: (1) high moisture uptake of PS-P4VP porogen (6.7 wt%), (2) increased level of the residual Si-OH groups on the pores surface resulting from incomplete crosslinking at low cure temperature at 250 oC due to steric effect and additional interaction by the polar pyridine moiety of porogen, and possibly (3) increased moisture uptake at MSQ/PS-P4VP-Au substrate or porous MSQ-Au substrate interface.
For a tri-block copolymer, PS-PB-SP porogen, the moisture uptake in MSQ/PS-PB-PS hybrid films were much lower, ≤ 1.0 wt% as compared to MSQ/PS-P4VP hybrid films, ≤ 3 wt%. For example, at 10% loading, the moisture adsorption of MSQ/PS-PB-PS films (1 wt%) was lower than MSQ/PS-P4VP films (1.67 wt%). The difference primarily originated from the low moisture uptakes of pure PS-PB-PS porogen, 1.8 wt% compared to 6.7 wt % in pure PS-P4VP due to its polar pyridine moiety. We also observed that moisture uptake in MSQ/ PS-PB-PS hybrid films did not increase with increasing loading, instead remained relatively constant. The deviation from linear model could be attributed to increased level of moisture uptake at film/Au interface in QCM case. Overall, a hydrophobic PS-PB-PS as high temperature porogen could reduce moisture adsorption of hybrid films significantly as compared to PS-P4VP porogen.
HMDS pre-treated porous MSQ films cured at 400 oC showed 11-17% reduction in moisture uptake could be attributed to the elimination of residual silanol groups, which played a minor role (< 20%) in the overall moisture uptake. Based on our studies in the thesis, such moisture adsorption was believed to be physical sorption
mode by forming a multilayer H2O adsorbent through long-range Van der Waals force with the hydrogen-bonded Si-OH--H2O, which was formed immediately after sample preparation. Elimination of such Si-OH groups required either by high-temperature annealing (> 280 oC) or chemical reaction such as HMDS treatment employed in this thesis. Moreover, the variation of dielectric constant between HMDS modified and un-modified porous MSQ at dry and RH 100% films was very small. In contrast the HMDS modified and un-modified porous MSQ at dry and RH 100% films measured by QCM were more comparable and clear. Therefore, QCM was a powerful and sensitive tool for direct estimating amount of moisture adsorption in low-k films.
The diffusion behavior of moisture uptake and desorption in the MSQ/porogen hybrid and porous MSQ films were also investigated in this thesis. The sorption of moisture in porous MSQ and MSQ/high-temperature porogens (PS-P4VP and PS-PB-PS) was found to be Fickian diffusion and very fast (< 200 seconds) and the absorbed moisture could be completely desorbed or pumped out in a short time (< 200 sec), even though their equilibrium moisture uptake may Such reversible characteristics indicated the moisture sorption at 30 oC was purely in physical sorption mode. Therefore, for IC industry, a short outgassing pre-treatment step at room temperature or elevated temperature can be easily added in the low-k integration steps to eliminate the trapped moisture avoiding any blistering or delamination.
Furthermore, the diffusion constants of the MSQ/porogen hybrid and porous MSQ films were obtained by fitting the sorption curves based on Fickian diffusion. It was found that the diffusion coefficients of porous MSQ films (400 oC cure) at porogen loading ≤ 20% were relatively constant ranging from 1.0x10-15 to 2.0 x10-15 m2/sec, while the diffusion coefficient of PS-P4VP porogen film was much higher at 2.4×10-14 m2/sec. The unvarying diffusion coefficients in MSQ/PS-P4VP system
of the porous or hybrid porous low-k films. Such thin but dense layer could serve as a diffusion barrier layer to prevent precursor penetration from hybrids or porous films.
The skin layer would be beneficial for MSQ/porogen hybrids in the Solid-FirstTM scheme or porous MSQ to be processed in the damascene technology.
In contrast, no skin layer was observed for MSQ/PS-PB-PS system. The formation mechanism of such a dense layer in MSQ/PS-P4VP system was proposed based on the amphiphilic nature of porogen and the solvent evaporation rate as dictated by its boiling point. For spin-coated MSQ/PS-P4VP/n-butanol system, the top of the as-deposited film was first to form a thin layer due to fast evaporation of solvent near the top during spin-coating step, while the evaporation of bulk n-butanol solvent was still relatively low at room temperature. In contrast, no skin layer was found in MSQ/PS-PB-PS hybrid films because the low boiling point (66 oC) of MSQ/PS-PB-PS solvent, tetrahydrofuran (THF) would outgas relatively fast and made it difficult to form any skin layer.
Based on moisture uptake, diffusion behavior analysis using QCM at 30 oC and dielectric properties using CV-dot measurement, we concluded the moisture uptake in porous MSQ films or MSQ/high-temperature porogen hybrid films was sorely in physical sorption as evidenced by the reversible sorption/desorption behavior for all the samples in this thesis. The moisture uptake in our samples included the following physical sorption modes through Van der Waals long-range force with (1) available surface area within the MSQ or porogen matrix, inside the pores, and at the MSQ/substrate or porogen/substrate interface, which contributed < 80% of moisture uptake, and (2) available hydrogen-bonded Si-OH--H2O sites, which were formed immediately after sample preparation, which contributed < 20% of moisture uptake.
References
1. M.T. Bohr, IEEE International Electronic Device Meeting, 241 (1995).
2. Y. H. Wang and R. Kumar, J. Electrochem. Soc. 151, 73 (2004).
3. S. J. Martin, J. P. Godschalx, M. E. Mills, E. O Shaffer and P. H. Townsend, Adv Mater. 12, 1769 (2000).
4. S. Malhouitre, C. Jehoul, J. V. Aelst, H. Struyf, S. Brongersma, L. Carbonell, I.
Vos, G. Beyer, M. V. Hove, D. Gronbeck, M. Gallagher, J. Calvert and K.
Maex, Micro. Eng. 70, 302 (2003).
5. M. L. Che, C. Y. Huang, S. Choang, Y. H. Chen, Y. L. Wang, and J. Leu, ECS Trans. 6, 591 (2007)
6. C.C. Chang, S. K. Jangjian and J. S. Chen, J. Electrochem. Soc. 153, 901 (2006).
7. International Technology Roadmap for Semiconductor, Executive summary, 2005.
8. National Technology Roadmap for Semiconductor (NTRS), 1997 edition (Semiconductor Industry Association, San Jose, California)
9. R. J Gutmann, IEEE Trans. Microw. Theory Tech. 47, 667 (1999).
10. H. D. Young, R. A . Freedman, Physics (Addison-Wesley, Massachusetts 1995)
11. D. I. Bower, An Introduction to Polymer Physisc(Cambridge University, Chapter 9, 2002)
12. G. Huougham, G. Tesoro, A. Viehbeck and J. D. Chapple-Sokol, Macromolecules, 27, 5964 (1994)
13. C. H. Ting, T.E. Seidel, Materials Research Society Symposium - Proceedings, Low-Dielectric Thin Films for Micoelectronics Applications, 1995
14. P.V. Zant, Microchip Fabrication : a practical guide to semiconductor processing (McGraw-Hill, 2001)
15. K. Mikagi, H. Ishikawa, T. Usami, M. Suzuki, K. inoue, N. oda, S. Chikaki, I.
Sakai and T. Kikkawa, IEEE International Electronic Device Meeting, 365 (1996)
16. Y. L. Cheng, Y. L. Wang, C.P. Liu, Y. L. Wu, K. Y. Lo, C. W. Liu, J. K. Lan, Mater. Chem. Phys, 150, 83 (2004)
17. Y. H Wang and R. Kumar, J. Electrochem. Soc, 151, 73 (2004)
18. C. C Chiang, M. C. Chen, L. J. Li, Z. C. Wu, S. M. Jang, and M. S. Liang, J.
Electrochem. Soc, 151, 612 (2004)
19. T. B. Casserly, K. K. Gleason, Plasma Process. Polym, 2, 679 (2005)
20. Y. C. Sil, Y. Y. Hun, L. K. Man, L. H. Ju and C. C.Kyu, Thin Solid Films, 26, 50 (2006)
21. Rusil, M. R. Wang, T. K. S. Wang, M. B. Yu and C. Y. Li, J. Electrochem. Soc, 152, 838 (2005)
22. M. R. Wang, Rusil, J. L. Xie, N. Babu, C.Y. Li and K. Rakesh, J. Appl. Phys, 96, 829 (2004)
23. A trademark of Novellus (www.novellus.com
24. A trademark of Applied Materials (www.appliedmateraials)
25. http://www.read-electronics.com/semiconductor/index.asp?layout=articlePrint
&articleID=CA279106
26. R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuki, Chem. Rev, 95, 1409 (1995)
27. R. Franco, A. K. Kandalam and R. Pandy, J. Phys. Chem, 106, 1709 (2002) 28. P. S. Ho, J. Leu and W. W. Lee, Low Dielectric Cinstant Materials for IC
Application, Chapter 6 (Springer, 2002)
29. H. C. Liou and J. Pretzer, Thin Solid Films, 335, 186 (186)
30. S. J. Martin, J. P. Godschalx, M. E. Mills, E. O. Shaffer and P. H. Townsend.
Adv. Mater, 23 , 1769 (2000)
31. http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=18308274re ference/EE times http://xx
32. R. W. Jones, Fundamental Principles of Sol-Gel Technology (London, The Institute of Metals, 1989)
33. S. Loo, S. Idapalapati, S. Wang. L. Shen and S. G. Mhaisalkar, Scripat Materials, 57, 1157 (2007)
34. I. Sugiura, N. Misawa, S. Otsuka, N. Nishikawa, Y. Iba, F. Sugimoto, Y. Setta, H. Sakai, Y. Koura, K. Nakata, Y. Mizushima, T. Suzuki, H. Kitada, N.
Shimizu, S. Nakai, M. Nakaishi, S. Fukuyama, T. Nakamura, E. Yano, M.
Miyajima and K. Watanabe, Micro. Eng, 82, 380 (2005)
35. A. Sayari, I. Moudrakovski, J. S reddy, C. I. Ratcliffe, J. A. Pipmeester and K.
F. Preston, Chem. Mat, 8, 2080 (1996)
36. J. M. Thomas, O. Terasaki, P. L. Gai, W. Zhou and J. Gonzalez-Calbe, Accounts Chem, Res, 34, 583 (2001)
37. Y. H. Sakamoto, M, Kaneda, o. Terasaki, D. Y. Zhou, J. M. Kim, G. Stucky, J.
Shin and R. Ryoo, Nature, 408, 449 (2000)
38. M. Kruk, M. Jaroniec, Y. Sakamoto, O. Terasaki, R. Ryoo and C. H. Ko, J.
Phys. Chem. B, 104, 292 (2000)
39. M.S. Wong, H. C. Huang and J. Y. Ying, Chem. Mat, 14, 1961 (2002) 40. T. R. Pauly and T. J. Pinnavaia, Chem. Mat, 13, 987 (2001)
41. M. S. Wong, E. S. Jeng and J. Y. Ying, Nano. Lett, 1, 637 (2001)
42. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuil and J. S. Beck, Nature,
43. J. S. Beck, J. C. Vartuil, W. J. Roth and M. E. Leonowicz, J. Am. Chem. Soc, 114, 10834 (1992)
44. Q. Huo, D. I. Margolese, U. Ciesla, D. G.. Demuth, and P. Feng, Chem. Mat, 6, 1176 (1994)
45. Q. Huo, D. I. Margolese, U. Ciesla, P. Feng, T. E. Gier, and G. D. Stucky, Nature, 368, 317 (1994)
46. P. T. Tanev and T. J. Pinnavaia, Science, 267, 865 (1995)
47. S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269, 1242 (1995) 48. D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F.
Chmelka and G. D. Stucky, Science, 279, 548 (1998)
49. D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chelka and G. D. Stucky, J. Am. Chem.
Soc, 120, 6024 (1998)
50. M. S. Wong and J. Y. Ying, Chem. Mat, 10, 2067 (1998)
51. M. R. Porter, Handbook of Surfactant (Chapman and Hall, New york, 1991 ) 52. K. Mosig, T. Jacobs, K. Brennan, M. Rasco, J. wolf and R. Augur, Micro. Eng,
64, 11(2002)
53. J. Tan, Z. W. Zhong and H. M. Ho, Micro. Eng, 81, 75 (2005)
54. Z. Chen, K. Prasad, C. Li, N. Jiang and D. Gui, IEEE Trans. Device Mater.
Reliab., 5, 133 (2005)
55. T. Abell and K. Maex, Micro. Eng, 76, 16 (2004)
56. A. M. Hoyas, J. Schuhmacher, C. M. Whelan, J. P. Celis and K. Maex, Micro.
Eng, 76, 32 (2004)
57. Z. Chen, K. Prasad, C. Y. Li, P. W. Lu, S. S. Su, L. J. Tang, D. Gui, S.Balakumar, R. Shu, and R. Kumar, Appl. Phys. Lett, 84 , 2442 (2004).
58. C. Jezewski, C. J. Wiegand, J. wiegand, D. Ye, A. Mallikarjunan, D. Liu, C.
Jin, W. A. Lanford, G. C. Wang, J. J. Senkevich and T. M. Lu, J. Electrochem.
Soc, 151, 157 (2004)
59. V. Jousseaume, M. Fayolle, C. Guedj, P. H. Haumesser, C. Huguet, F. Pierre, R. Pantel, H. Feldis and G. Passmard, J. Electrochem. Soc, 152, 156 (2005) 60. S. Malhouitre, C. Jehoul, J. V. Aelst, H. Struyf, S. Brongersma, L. Carbonell, I.
Vos, G. Beyer, M. V. Hove, D. Gronbeck, M. Gallagher, J. Calvert and K.
Maex, Micro. Eng. 70, 302 (2003).
61. E. G. Liniger and E. E. Simonyi, J. Appl. Phys, 96, 3482 (2004)
62. J. Yao, A. Iqbal, H. Juneja and F. Shadman, J. Electrochem. Soc, 154, 199 (2007)
63. C. C. Chang, S. K. Jangjian and J. S. Chen, J. Electrochem. Soc, 153, 901 (2006)
64. T. Kikkawa, S. Kuroki, S. Sakamoto, K. Kohmura, H. Tanaka and N. Hate, J.
Electrochem. Soc, 152, 560 (2005)
65. A. P. Singh, D.D. Gandhi, E. Lipp, M. Eizenberg and Gramanath, J. Appl.
Phys, 100, 114504 (2006)
66. S. Rogojevic, A. Jain, W. N. Gill and J. Plawsky, Eeletrochem. Solid-state Lett, 5, 22 (2002)
67. S. I. Kuroki and T. Kikkawa, J. Electrochem. Soc, 153, 759 (2006) 68. A. R. Forouhi and I. Bloomer, Phys. Rev. B. 34, 7018 (1986)
69. P. R. Griffiths and J. A. deHaseth, Fourier Transform Infrared Spectrometry.
(wiley, 1986)
70. C. Lu and A.W. Czanderna, Applications of Piezoelectric Quartz Crystal Microbalance, (Elsevier, New York, 1984).
71. P. S. Ho, J. Leu, W. W. Lee, Low Dielectric Constant Materials for IC Application, chapter 2 (Springer 2002).
Vac. Sci. Technol B. 17, 205 (1999)
73. C. Y. Wang, J. Z. Zheng, Z. X, Shen, Y. Xu, S. L. Lim, R. Liu and A. C. Huan, Surf. Interface Anal. 28, 97 (1999).
74. J. Yao, A. Iqbal, H. Juneja and F. Shadman, J. Electrochem. Soc, 154, 199 (2007)
75. J. Crank, The Mathematics of Diffusion, (Oxford University, London, 1975) 76. D. E. Haas, J. N. Quijada, S. J. Picone and P. Birnie, Proc SPIE Int Soc Opt
Eng, 3943, 280 (2000)
77. A. Iqbal, H. Juneja, J. Yao and F. Shadman, AICHE, 52, 1586 (2006)
78. J. Proost, E. Kondoh, G. Vereeche, M. Heyns and K Maex, J. Vac. Sci.
Technol. B, 16, 2091 (1998)
Appendix A
QCM data curve of Moisture uptakes of porous, HMDS modified, MSQ/PS-P4VP hybrid films and PS-P4VP films.
-200 0 200 400 600 800 1000 1200 1400 1600 1800
-0.2
Hybrid films with 10 wt%
porogen laoding
(a) Hybrid film with 10 wt% loading
-200 0 200 400 600 800 1000 1200 1400 1600 1800
0.0 0.5 1.0 1.5 2.0
2.5 Hybrid films with 20 wt%
porogen laoding
moisture uptake wt%
Time (sec)
-200 0 200 400 600 800 1000 1200 1400 1600 1800
Hybrid films with 30 wt%
porogen laoding
Moisture uptake wt%
Time (sec)
(c) Hybrid film with 30 wt% porogen loading
porous films after 10 wt% porogen remove 7.9 % porosity
(d) Porous MSQ with 7.9 % porosity
0 200 400 600 800 1000 1200
porous films after 20 wt% porogen remove
Moisture uptake wt%
Time (sce)
19.3% porosity
(e) Porous MSQ with 19.3 % porosity
0 100 200 300 400 500 600
porous films after 30 wt% porogen remove
Moisture uptake wt%
Time (sec)
29.1% porosity
0 100 200 300 400
(g) Porous MSQ after HMDS modification
0 100 200 300 400 500 600
(h) Porous MSQ after HMDS modification
-100 0 100 200 300 400 500 600 700
(i) Porous MSQ after HMDS modification
0 1000 2000 3000 4000 5000
-1
Appendix B
QCM data curve of Moisture uptakes of MSQ/PS-PB-PS hybrid film
0 100 200 300 400 500 600
(a) Hybrid film with 5 wt% loading
-100 0 100 200 300 400 500 600 700 with 10 wt% porgen loading
(b) Hybrid film with 10 wt% loading
0 100 200 300 0.0
0.5 1.0
Moisture uptake wt%
Time (sec)
MSQ/ps-pb-ps hybrid films with 15 wt% porogen loading
(c) Hybrid film with 15 wt% loading
0 100 200 300
0.0 0.5 1.0
Moisture uptake wt%
Time (sec)
MSQ/ps-pb-ps hybrid films with 15 wt% porogen loading
(d) Pure porogen