Effects of Etch Rate on Plasma-Induced Damage to Porous Low-$k$ Films

We investigated the effects of etch rate on low-k damage induced by dry etching under CF4, CF4/O2, and C4F6/O2/Ar chemistry conditions. The amount of damage increases with decreasing etch rate in all chemistries. This is because the amount of fluorine or oxygen radical diffusion increases with plasma exposure time. These radicals extract CH3 groups from the low-k film or oxidize the film. To reduce damage to the lowest level possible, it is necessary to suppress the effect of the damage diffusion using etching conditions where the etching speed is higher than the diffusion speed of the damage.