Frustrated Total Internal Reflection Spectra of Diazoquinone–Novolac Photoresist Films

Abstract

Radiation-induced effects in thin films of diazoquinone–novolac photoresists on silicon irradiated with high-energy electrons (~5 MeV) were investigated by frustrated total internal reflection (FTIR) IR Fourier spectroscopy. It was found that irradiation with electrons at a dose of more than 3×10^15 cm^–2 leads to decrease of the integral absorption at wave numbers in the region of 3700–400 cm^–1. The intensity of bands due to the –O–H– and particularly aliphatic –C–H– bonds is increased most strongly during electron irradiation. At a dose of Φ = 1×10^17 cm^–2 the intensity of the bands due to the methylene (–CH2–) and methyl (–CH3) groups is comparable with the noise level. The intensity of the band at ~1600 cm^–1, due to the vibrations of the aromatic ring, does not change at radiation doses in the range of 3×10^14—1×10^17 cm^–2. The obtained experimental data indicate strong cross-linking of the polymeric components during irradiation with electrons. It was found that the radiation-induced changes in the FTIR spectra depend on the type of photoresist (FP9120 and S1813 G2 SP15). The experimental relationships of change in the optical characteristics of thin films of photoresists due to electrons are explained in terms of the radiation chemistry of diazoquinone–novolac resins.