The Influence of Resist Components on Image Blur in a Ppatterned Positive-Tone Chemically Amplified Photoresist

Post-exposure bake-induced blurring of the latent image in a chemically amplified photoresist may limit the extendability of this resist technology to printing of nanoscale features. It had been proposed that blurring is caused by thermally-assisted diffusion of photogenerated acid, however our experimental and kinetic modelling investigations of coupled reaction-diffusion in a resist system consisting of a photoacid generator in p-t-butyloxycarbonyloxystyrene (PTBOCST) has shown that the very high efficiency of acidolysis chemistry at the edge of an exposed region is actually responsible for blurring. Studies of the role of added base and the impact of photoacid generator size on blur support this view. These previous studies were performed with a 1-dimensional geometry. In order to test the relevance of the 1-D blurring model to pattern formation, we have carried out new investigations of blurring in dense line-space patterns using the same PTBOCST resist systems as in our earlier work. Resist films were imprinted with 866 nm and 192 nm pitch gratings generated by interferometric lithography using 257 nm light. The extent of deprotection over a range of doses and bake times at 85 C was measured by infrared spectroscopy, and compared to results of simulations of the bake process using the experimental aerial image and kinetics determined in the previous work. Experiment and predictions are in good agreement in all cases, indicating that the 1-dimensional kinetics are extendable to the 2-dimensional case. The simulations permit visualization of the relationship between the acid latent image and the developable image that forms in the polymer, enabling a deeper appreciation of the influences of the resist components and of resist processing conditions on latent image transformations during post-exposure bake.