Radiation-Induced Processes in Electron-Irradiated Films of Negative Phenol-Formaldehyde Photoresist on Silicon

It was found that radiation-induced processes in films of negative photoresist NFR 016D at doses up to 2 × 10¹⁵ cm^–2 occur mainly with the participation of residual solvent molecules or on by-products of the photoresist film synthesis. After irradiation, absorption bands with maxima at 1717 (stretching vibrations of C=O bonds), 1068, and 1009 cm^–1 (vibrations of C–O–C bond in methyl-3-methoxypropylate solvent) disappear in the attenuated total internal reflection spectra of the photoresist. At irradiation doses above 1 × 10¹⁶ cm^–2, significant changes in the intensity of the bands associated with the main component of the photoresist (phenol-formaldehyde resin) were observed. A noticeable transformation of the spectrum occurs in the region of 1550–1700 cm^–1, in which stretching vibrations of C=O bonds are observed. At irradiation doses above 2 × 10¹⁶ cm^–2, the intensities of the bands caused by stretching vibrations of CH₂ and CH groups decrease (bands with maxima at 2925 and 3012 cm^–1, respectively). The experimental results indicate a change in the composition of substituents at the carbon ring and the formation of conjugated double C=O bonds when the photoresistive film is irradiated with electron doses above 2 × 10¹⁶ cm^–2.