Preparation of low-k nanoporous SiO2 films by plasma-enhanced chemical vapor deposition

Low-dielectric constant (low-k) materials of porous SiO₂ films were deposited at 300°C by plasma enhanced chemical vapor deposition (PE-CVD) using SiH₄-O₂ mixtures. The [O₂]/[SiH₄] ratio was maintained at 1.5, in which oxide films having a stoichiometric composition can be obtained. It was found that the deposition rate increases linearly with total flow rate of SiH₄ and O₂ gases, and the values of k decrease monotonously with increasing deposition rate. No H-related bonds are found in the infrared (IR) spectrum. The value of k for a film prepared at a deposition rate of 56 nm/min was estimated to be 3.4. After an initial annealing at 400°C, a thickness loss for the film was near 10%. It suggests that micro-voids exist in the films. These results indicate the possibility to further reduce the k value of PE-CVD porous SiO₂ films and the potential to incorporate such films in the interconnect structure of ultra larger scale integrated circuits (ULSI)