Novel Low-k Dual-phase Materials Prepared by PECVD
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Novel Low-k Dual-phase Materials Prepared by PECVD Alfred Grill and Vishnubhai Patel IBM Research Division, T.J.Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT Dielectric materials based on Si, C, O, H (SiCOH) have been demonstrated previously with dielectric constants of about 2.8. This value could be potentially further reduced by increasing/introducing porosity in the SiCOH films. Depositing multiphase films containing at least one thermally unstable phase and annealing the films to remove this labile phase from the material could create the enhanced porosity. Dual-phase materials, SiCOH-CH, have been prepared in the present study by PECVD from mixtures of a SiCOH precursor with a hydrocarbon. The films have been characterized as-deposited and after thermal anneals of up to 4 hours at 400 0C. The atomic composition of the films has been determined by RBS and FRES analysis and their optical properties have been determined by FTIR and n&k measurements. Metal-insulator-silicon structures have been used to measure the electrical properties of the dualphase films. After an initial anneal at 400 oC, accompanied by a significant loss of CH and some SiH species and a thickness loss of up to 50%, the films stabilized. Depending on the deposition conditions and concentration of the CH precursor in the feed gas, the dielectric constant decreased by 10-15% during the stabilization anneal and reached values as low as 2.4. These initial results indicate the possibility to further reduce the dielectric constant of PECVD produced SiCOH films and the potential to incorporate such films in the interconnect structures of future ULSI chips. INTRODUCTION The electrical properties of the interconnect dielectric (ILD) become as critical as the those of the metal wiring for achieving high performance in the shrinking, high speed ULSI devices. Low dielectric constant materials are required for the ILD to reduce propagation delays, cross-talk noise between metal wires, and power dissipation from RC coupling. The research done on lowdielectric constant (low-k) materials is well reflected in the proceedings of this symposium of the last 5 years.[1] However, the search for an integratable low-k dielectric material is still a work-in progress which appears to elude the original roadmap for low-k interconnect dielectrics.[2] Some promising low-k materials can be deposited by spin-on techniques while other can be prepared by plasma enhanced chemical vapor deposition (PECVD) processes. The latter can produce films that are more crosslinked than spin-on polymeric films and be therefore mechanically tougher. Low-k materials comprised of Si, C, O and H, (SiCOH films) and prepared by plasma enhanced chemical vapor deposition (PECVD) have been reported previously by the present authors [3] and are being offered by equipment vendors under different trade names.[2] The materials, often referred to as carbon-doped oxides, are characterized by dielectric constants of about 2.8, almost independent of the source.
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