Radiation-Induced Processes in the Films of Negative Phenol-Formaldehyde Photoresist on Silicon Irradiated by Electrons

The aim of the work was to use the method of the attenuated total reflection (ATR) and the Fourier IR-spectroscopy for the study of the film of the negative phenol-formaldehyde photoresist NFR 016D4 deposited on the surface of silicon wafers by centrifugation and irradiated by electrons with energy of 5 MeV. It was established that the radiation-induced processes in the NFR 016D4 films at doses up to 2∙1015 cm-2 proceed mainly with the participation of the residual solvent molecules or on by-products of the synthesis of the photoresist film. As a result, after irradiation in the ATR spectra of the photoresist, the absorption bands with maxima at 1717 (valence vibrations C=O bonds), 1068 and 1009 cm-1 (C-O-C bonds in the solvent – methyl-3-methoxypropylate) disappeared. At doses of irradiation over 1∙1016 cm-2, significant changes were observed in the intensity of the bands associated with the main component of the photoresist (phenol-formaldehyde resin). So, a noticeable transformation of the spectrum occurred in the interspace of 1550–1700 cm-1, in which valence vibrations of C = O bonds were observed. At doses of irradiation over 2∙1016 cm-2, there was a decrease in the intensities of bands due to valence vibrations in CH2 and CH groups (bands with maxima at 2925 and 3012 cm-1, respectively). The obtained experimental results indicate a change in the composition of the deputies in a carbon ring and the formation of conjugated double C=O bonds when the photoresist film was irradiated with doses of electrons over 2∙1016 cm-2. Significant changes in the intensity of the bands of valence vibrations of the aromatic ring with a maximum of 1503 cm-1 were not noted. However, there was a bruise and displacement into the low-energy area of the band with a maximum at 1436 cm-1, responsible for the valence vibrations of the aromatic ring associated with the CH- bridge.