Dielectric Materials Research for Advanced Microelectronic Devices - History

From a historical point of view, the search for new low-k and ultra low-k materials has always been dictated by industrial needs, resulting in a strong connection between fundamental research and technology. Although, a variety of potential candidates have been reported in the literature during the past decade, integration is the deciding factor driving the selection of the most promising materials for a given technology node [1]. For instance, the industry flirted briefly with organic polymers [2-7]. Besides the anticipated thermal stability challenges, this class of materials, known to be tough and crack-resistant, had other issues, such as softness, large coefficient of thermal expansions (CTE) and delamination. While most of these problems were mitigated by material reengineering and chip redesign, solutions occurred too late, relegating the organic polymers to possible hybrid build applications [8]. For the new low-k materials, it was expected that their electrical and mechanical properties would be comparable to those of silicon dioxide [9, 10], the insulating material of reference for the quite conservative semiconductor industry. Chemical modification of the silicon network, first by introduction of fluorine and eventually by the addition of carbon, was then adopted as the lower risk path to introducing low-k materials in the back-end-of-the-line (BEOL) [1]. At that time, silicates and organosilicates emerged as the dominant candidates. They can be deposited by both spin-on and chemical vapor deposition (CVD) processes. However, the final thin-film properties are in large part dictated by the chemical structure of the deposited film, a result of both the precursor or resin chemistry and the deposition process. From before 1997 until now, plasma-enhanced chemical vapor deposition (PECVD) has been the method of choice for depositing silicon dioxide (SiO2), fluorine-doped oxides (F-SiO2), carbon-doped oxides (SiCOH: elementally descriptive but not representing the stoichiometry) and porous carbon-doped oxides (p-SiCOH). PECVD SiCOH materials were successfully implemented in IBM microprocessors: at the 90 nm (k=3.0) and 65 nm (k=2.7) technology nodes in 2004 and 2006, respectively. PECVD materials containing additional porosity (p-SiCOH) appeared for the first time in high volume manufacturing in 2008. The challenges in designing dielectric insulators that meet all the BEOL requirements (electrical, thermal and mechanical) have been the source of many publications over the last 15 years [1]. Among them, many excellent reviews have been published, addressing the different aspects of these dielectric materials: physical properties [7, 11-13], integration requirements and challenges [14, 15], characterization [9, 16-19] and chemistry [1]. For advanced and future technologies, the addition of porosity at levels necessary to obtain dielectric constants of 2.4 and beyond has exacerbated already known integration issues [14]. In particular, the processing induced damage, the decrease in material mechanical properties and the reduced breakdown voltage present serious concerns for the reliability of these advanced structures.

  1. W. Volksen, R. D. Miller and G. Dubois, Low Dielectric Constant Materials, Chem. Rev., 110, 56-110 (2010).
  2. K. Goto, T. Akiike, K. Konno, T. Shiba, M. Patz, M. Takahashi, Y. Inoue and M. Matsubara, Thermally stable polyarylenes with low dielectric constant: direction towards the lowest limit of dielectrics, J. Photopolym. Sci. Technol., 15, 223-229 (2002).
  3. G. Maier, Low dielectric constant polymers for microelectronics, Prog. Polym. Sci., 26, 3-65 (2001).
  4. T. Miwa, Polyimides in microelectronics applications, J. Photopolym. Sci. Technol., 14, 29-32 (2001).
  5. H. Treichel, G. Ruhl, P. Ansmann, R. Wurl, C. Muller and M. Dietlmeier, Low dielectric constant materials for interlayer dielectric, Microelectron. Eng., 40, 1-19 (1998).
  6. H. Treichel, B. Withers, G. Ruhl, P. Ansmann, R. Wurl, C. Muller, M. Dietlmeier and G. Maier, Low-dielectric-constant materials for interlayer dielectrics, in Handb. Low High Dielectr. Constant Mater. Their Appl., (Eds), Vol. 1, 1999.
  7. G. Dubois, W. Volksen and R. D. Miller, Spin-On Dielectric Materials, in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.
  8. T. Nakamura and A. Nakashima, Robust multilevel interconnects with a nano-clustering porous low-k (k < 2.3), in Proceedings of IEEE Int. Interconnect Technol. Conf., 7th, Burlingame, CA, USA, pp. 175-177 (2004).
  9. T. Homma, Low dielectric constant materials and methods for interlayer dielectric films in ultralarge-scale integrated circuit multilevel interconnections, Mater. Sci. Eng., R, R23, 243-285 (1998).
  10. Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition., John Wiley & Sons, New-York, 1992.
  11. A. Grill, Low and ultralow dielectric constant films prepared by plasma-enhanced chemical vapor deposition, in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.
  12. A. Grill, Porous pSICOH Ultralow-k Dielectrics for Chip Interconnects Prepared by PECVD, Annu. Rev. Mater. Sci., 39, 49-69 (2009).
  13. B. D. Hatton, K. Landskron, W. J. Hunks, M. R. Bennett, D. Shukaris, D. D. Perovic and G. A. Ozin, Materials chemistry for low-k materials, Mater. Today, 9, 22-31 (2006).
  14. R. J. O. M. Hoofman, V. H. Nguyen, V. Arnal, M. Broekaart, L. G. Gosset, W. F. A. Besling, M. Fayolle and F. Iacopi, Integration of low-k dielectric films in damascene processes, in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.
  15. M. Morgen, E. T. Ryan, J.-H. Zhao, C. Hu, T. Cho and P. S. Ho, Low dielectric constant materials for ULSI interconnects, Annu. Rev. Mater. Sci., 30, 645-680 (2000).
  16. M. R. Baklanov, Porosity of Low Dielectric Materials. Ellipsometric Porosimetry., in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.
  17. D. W. Gidley, H.-g. Peng and R. Vallery, Porosity of Low Dielectric Materials. Positron Annihilation Spectroscopy, in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.
  18. K. Maex, M. R. Baklanov, D. Shamiryan, F. Iacopi, S. H. Brongersma and Z. S. Yanovitskaya, Low dielectric constant materials for microelectronics, J. Appl. Phys., 93, 8793-8841 (2003).
  19. C. L. Soles, H.-J. Lee, B. D. Vogt, E. K. Lin and W.-L. Wu, Porosity of Low Dielectric Materials. Structure Characterization of Nanoporous Interlevel Dielectric Thin Films with X-Ray and Neutron Radiation., in Dielectric Films for Advanced Microelectronics, M. Baklanov, K. Maex and M. Green (Eds), Wiley, New-York, 2007.