Plasma is extensively used for the etching/ashing of low-dielectric (low-k) films. However, since low-k films, such as SiOC films, are vulnerable to plasma irradiation, they are severely damaged during plasma processes, such as the extraction of methyl groups from low-k films. As a result, plasma irradiation increases the dielectric constant of low-k films and reduces the reliability of Cu/low-k interconnects. In previous work, the authors achieved highly selective and low-damage etching processes for low-k films by using their developed neutral beam process instead of the conventional plasma process. They have now investigated the damage mechanism in low-k films (porous SiOC films) during plasma processes by clarifying the effects of ions, radicals, and photons in plasma. First, they compared the damage in SiOC films etched by the conventional plasma process and the neutral beam process. Their results show that plasma processes change the structure of the SiOC film deeply within the film (over 100 nm in depth) and increase the film's dielectric constant, whereas the neutral beam process maintains the structure of the SiOC film. Additionally, they found that when a combination of the neutral beam process and a 172 nm excimer lamp is used, photon irradiation enhances the extraction of methyl groups from the SiOC film by breaking Si-C bonds in the film. These results show that photon irradiation plays a very important role in the damage mechanism in low-k films during plasma processes.