STABILIZING PROCESSING OF NEGATIVE PHOTORESIST FILMS OF THE AZ nLOF20XX SERIES ON SILICON

Films of negative photoresists (PR) AZ nLOF2020 and AZ nLOF2070 with a thickness of ~ 6.0 microns deposited on the surface of silicon wafers by centrifugation have been studied using microindentation and IR Fourier spectroscopy methods. It is shown that after irradiation with light with λ = 404 nm for 106 s and subsequent drying at 115 °C for a duration of 60 s, a shift to the high-energy region of interference bands maxima is observed in the reflective- absorption spectra of photoresistive films. It is caused by a decrease in the thickness of the FR film due to evaporation of the solvent during the drying process. These processes occur more intensively in AZ nLOF2020 films, in which the interference bands shift was ~ 9%, while in AZ nLOF2070 films it did not reach 1%. It is shown that the absorption bands with maxima at 1070 and 1100 cm⁻¹, due to asymmetric and symmetrical valence vibrations of C-O-C bonds in aliphatic esters, and at 2940 cm⁻¹, due to asymmetric valence vibrations of CH₃ bonds, are associated with a solvent. It was found that the microhardness of the AZ nLOF20XX series films increases after stabilizing drying, which is due to the crosslinking of phenol-formaldehyde resin molecules – the basis of the photoresist. The resulting experimental data is explained taking into account the ordering of the structure of the photoresistive film near the PR/silicon interface due to the orientation of the molecules and the presence of AZ nLOF2020 films with a higher concentration of residual solvent.

negative photoresist, silicon, IR Fourier-spectroscopy, microhardness, solvent evaporation, drying