Mechanism And Kinetics Of Silylation Of Resist Layers From The Gas Phase

Abstract

The silylation from the gas phase of photoresists based on diazoquinone and novolac or polyvinylphenol, which can be used in dry developable systems has been investigated. It is shown that the phenolic hydroxyl groups are almost completely silylated. The kinetics of the reaction have been followed by gravimetry, IR spectroscopy and Rutherford backscattering spectrometry. During the reaction a completely silylated, swollen layer is formed with a sharp front separating it from the unreacted resin. The rate controlling processes are the relaxation of the polymer and the diffusion of the reagent. When the relaxation is slow with respect to diffusion, linear reaction kinetics as in Case II diffusion are observed. When the relaxation is fast the reaction proceeds with the square root of time. The increase of the reaction rate with UV exposure of the resist is attributed to an increase in the relaxation rate of the resist. A model explains the higher photoselectivity of the reaction at elevated temperatures. Results with a number of model resists indicate that some diazoquinones can act as physical crosslinks between polymer chains via the formation of hydrogen bonds whereas the corresponding indenecarboxylic acids cannot. Due to the high content of silicon after the treatment these resists become highly etch-resistant towards oxygen plasmas.