Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy

Abstract

The modification of porous low-dielectric (low-k) SiOCH films by ashing plasma irradiation and subsequent exposure to air was investigated by in situ characterizations. Porous blanket SiOCH film surfaces were treated by a H2 or H2/N2 plasma in a 100-MHz capacitively coupled plasma reactor. The individual or combined effects of light, radicals, and ions generated by the plasmas on the chemical bonds in the porous SiOCH films were characterized using an in situ evaluation and by in situ Fourier-transform infrared reflection absorption spectroscopy (IR-RAS). In situ IR-RAS analysis revealed that the number of Si-OH, Si-H, and Si-NH2 bonds increased while the number of Si-CH3 bonds decreased during exposure to a H2 or H2/N2 plasma. Subsequent air exposure increased the number of Si-OH bonds by modifying Si-O-Si structures. The experimental results indicate that light emitted from a H2 or H2/N2 plasma can break Si-CH3 and Si-O-Si bonds and thereby generate dangling bonds. Radicals (e.g., NxHy and H radicals) can break Si-CH3 and Si-O-Si bonds and Si-NH2, Si–H, and Si-OH bonds could be formed. Si-NH2, Si-H, and dangling bonds react with moisture in the air cause the formation of Si-OH bonds. The dehydroxylation reaction on Si-OH was found to be the origin of Si-O-Si network structures. The mechanism of the degradation of porous low-k SiOCH films induced by a H2 or H2/N2 plasma is discussed based on the in situ characterization results.