From tribological coatings to low- k dielectrics for ULSI interconnects

Abstract

Hydrogenated diamond-like carbon (DLC) films, typically prepared as a wear- and corrosion-resistant coatings, can be modified by the adjustment of the plasma-enhanced chemical vapor deposition (PECVD) conditions to obtain materials with dielectric constants ( k) ranging from 3.3 to 2.7. Incorporation of fluorine in the DLC further reduces the dielectric constant to values as low as 2.4. The integration of the low- k materials in ultra large-scale integrated circuit (ULSI) chips imposes a significant number of requirements, which are not easily achieved by low- k dielectrics. The integration of DLC has been demonstrated up to two levels in a Cu-based damascene structure; however, FDLC could not be integrated by processing at the temperature of 400°C typically used in the back end of line (BEOL) processing. In order to improve the integration and reliability of the low- k materials, a hybrid composition of DLC and SiO 2 has been developed. Carbon-doped oxides (CDO), or SiCOH films, comprising Si, C, O, and H and deposited by PECVD, have achieved dielectric constant values lower than 2.8. The dielectric constant of such materials can be further lowered by depositing multiphase films, containing at least one thermally unstable phase, and annealing the films to remove this unstable phase from the material. This process enhances the atomic level porosity in the films and further reduces the dielectric constant. Dual-phase materials have been prepared by PECVD from mixtures of SiCOH precursors with organic precursors. Proper choice of precursor and optimization of the deposition conditions can reduce the dielectric constant of the stabilized films to values below 2.2.