Characteristics of low-k and ultralow-k PECVD deposited SiCOH films.
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Characteristics of low-k and ultralow-k PECVD deposited SiCOH films. A. Grill, V. Patel, K.P. Rodbell, E. Huang and S. Christiansen IBM T. J. Watson Research Center, Yorktown Heights, New York, USA. M. R. Baklanov XPEQT at IMEC, Leuven, Belgium ABSTRACT We have shown previously that the dielectric constants of PECVD prepared SiCOH dielectrics can be extended to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by adding an organic precursor to the tetramethylcyclotetrasiloxane (TMCTS) used for the preparation of the SiCOH dielectric and annealing the films to remove the thermally less-stable organic CHx fractions from the films, thereby adding porosity and reducing the density of the films. To assess the effects of the reduction of the dielectric constant on other physical properties of the material, the density and composition of the films have been determined by RBS and FRES and the porosity has been measured by PAS/PALS, SAXS and ellipsometric porosimetry. In addition the films have been characterized structurally and topologically by TEM and AFM. It has been found that addition of the organic precursor reduces the Si fraction in the films, however, there is no direct correlation between dielectric constant and film composition. The dielectric constant and density decrease with increasing porosity in the films, which reaches values of 30-39% for k values of 2.05. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05. This is significantly smaller than the pore size typically found in porous spin-on films and may provide an integration advantage compared to spin-on films having similar k values. INTRODUCTION The advancement in performance of ultra-large scale integrated (ULSI) circuits is still being hindered by the difficulties encountered in introducing new dielectrics into Si chip interconnection technology. The delay in the introduction of insulators of reduced dielectric constants is marked by continuous revisions outwards in time of the International Technology Roadmap for Semiconductors (ITRS) projections since 1997. The 2001 ITRS pushed out again low-k dielectric milestones, e.g. decelerating advances to ultralow-k dielectrics (k=1.6-2.2) from 2005 to 2009. [1] The determination of the best choice for low-κ dielectrics is still ongoing, with primary choices being spin-on polymers and PECVD glasses. The main contenders among the PECVD low-k dielectrics are amorphous materials from a group comprised of Si, C, O, and H which are deposited in conventional PECVD tools [2] and known by different names, including SiCOH, SiOCH, carbon-doped oxides (CDO), silicon-oxicarbides, organosilicate glasses (OSG) and several trade names given by the various suppliers who provide processes and tooling for these films. The generic term SiCOH will be used throughout this paper to refer to the films that we have developed. We have demonstrated elsewhere [3, 4] that it is possible to reduce the dielectric constants of SiCOH materials to values as low a
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