Recovery from Plasma-Process-Induced Damage in Porous Silica Low-k Films by Organosiloxane Vapor Annealing

Abstract

It was demonstrated that recovery from dry etching and ashing damage in porous silica low-k films occurred by 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) vapor 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 vapor annealing. Leakage current also returned to the initial level. Hydrofluoric acid wet etching revealed the sidewall damaged region in a porous silica trench due to plasma processes. The TMCTS vapor annealing was found to be effective for recovery from the sidewall damage. Fourier transformed infrared absorption spectroscopy indicated that the replacement of Si–CH3 bonds in low-k films by Si–O and Si–OH bonds occurred during plasma processes. The recovery mechanism involves hydrophobic bond (–CH3) reintroduction into the film followed by stable cross-linked poly(TMCTS) network formation on pore wall surfaces by TMCTS vapor annealing.