From Tribological Coatings to Low-k Dielectrics for ULSI Interconnects

Hydrogenated diamondlike carbon (DLC) films, typically prepared as a wear and corrosion resistant coating, can be modified by the adjustment of the PECVD deposition conditions to obtain materials with dielectric constants (k) ranging from 3.3 to 2.7. Incorporation of F in the DLC further reduces the dielectric constants to values as low as 2.4. The integration of the low-k materials in ULSI chips imposes a significant number of requirements, which are not easily achieved by the 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^oC typically used in the back end of the line (BEOL) processing. In order to improve the integrability and reliability of the low-k materials, a hybrid composition of DLC and SiO² has been developed. Carbon doped oxides (CDO), or SiCOH films, comprising Si, C, 0 and H and deposited by PECVD, have achieved dielectric constant values as 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 labile 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. By proper choice of precursor and optimization of the deposition conditions. the dielectric constant of the stabilized films can be reduced to values below 2.2.