Recovery of plasma process induced damage in porous silica low-k films by organosiloxane vapor post annealing

It is demonstrated that dry etching and ashing damage in porous silica low-k films is recovered by TMCTS (1, 3, 5, 7-tetramethylcyclotetra-siloxane) vapor post annealing. The increase in k-value after Ar/C₅F₈/O₂ plasma etching was reduced from 35% to 6.5% of the initial value (k=2.25) by TMCTS annealing. The leakage current was also recovered to the original level. The HF wet etching revealed that the gas chemistries both with and without oxygen caused the sidewall damaged region in the porous silica trench and the TMCTS annealing was effective to recover the sidewall damage. Fourier transformed infrared absorption measurements indicated that the replacement of Si-CH₃ bonds in low-k films by Si-O and Si-OH bonds occurred during the plasma treatments. The recovery mechanism is that hydrophobic bonds (-CH₃) were reintroduced into the film and a stable cross-linked poly(TMCTS) network was formed on the pore wall surfaces by the TMCTS post annealing.