Mechanism of plasma-induced damage to low-k SiOCH films during plasma ashing of organic resists

Plasma-induced damage to porous SiOCH (p-SiOCH) films during organic resist film ashing using dual-frequency capacitively coupled O2 plasmas was investigated using the pallet for plasma evaluation method developed by our group. The damage was characterized by ellipsometry and Fourier-transform infrared spectroscopy. Individual and synergetic damage associated with vacuum ultraviolet (VUV) and UV radiation, radicals, and ions in the O2 plasma were clarified. It was found that the damage was caused not only by radicals but also by synergetic reactions of radicals with VUV and UV radiation emitted by the plasmas. It is noteworthy that the damage induced by plasma exposure without ion bombardment was larger than the damage with ion bombardment. These results differed from those obtained using an H2/N2 plasma for resist ashing. Finally, the mechanism of damage to p-SiOCH caused by O2 and H2/N2 plasma ashing of organic resist films is discussed. These results are very important in understanding the mechanism of plasma-induced damage to p-SiOCH films.