Chemical mapping of patterned polymer photoresists by near-field infrared microscopy

Latent images obtained by deep-ultraviolet (DUV) patterning and post-exposure bake in the polymer system poly(t-butylmethacrylate) (PTBMA) resist/triphenyl sulfonium photoacid generator are characterized by infrared near-field microscopy (IR-NSOM). Chemical sub-group specificity is achieved in the infrared near-field images by using wavelengths tuned on the OH absorption band of the poly(methacrylate acid) (PMAA) resulting from the photoacid-catalyzed decomposition of t-butoxycarbonyl groups. The experimental images of the patterned thin polymer film are compared with predictions based on scalar diffraction theory calculations for the initial light illumination step through the mask. Partial disagreement between the theory and the experiment is observed, but only for certain line/space dimensions of the pattern. The results suggest a structure-dependent chemistry during the latent image development.