Stabilizing Treatment of Negative Photoresist Films of the AZ nLOF20XX Series on Silicon

Abstract

Films of negative photoresists (PR) AZ nLOF2020 and AZ nLOF2070 about 6.0 μm thick, deposited on the surface of monocrystalline silicon wafers by centrifugation, are studied using FTIR spectroscopy and microindentation methods. It is shown that after exposure to light with λ = 404 nm for 106 s and subsequent baking at 115°C for 60 s, a shift of the interference band maxima toward the high-energy region is observed in the reflection–absorption spectra of the photoresist films. It is caused by a decrease in the thickness of the PR film due to the evaporation of the solvent during baking. These processes occur more intensively in AZ nLOF2020 films, in which the shift of interference bands is ~9%, while in AZ nLOF2070 films it did not exceed 1%. It is shown that absorption bands with maxima at 1070 and 1100 cm–1, caused by asymmetric and symmetric stretching vibrations of C–O–C bonds in aliphatic ethers, and at 2940 cm–1, caused by asymmetric stretching vibrations of CH3 bonds, are associated with the solvent. It is established that the microhardness of AZ nLOF20XX series films increases after stabilizing baking, which is due to the cross-linking of phenol–formaldehyde resin molecules, the base of the photoresist. The obtained experimental data are explained by the ordering of the photoresist film structure near the PR/silicon interface due to the orientation of the molecules and the higher concentration of residual solvent in AZ nLOF2020.