Pattern characterization of deep-ultraviolet photoresists by near-field infrared microscopy

Chemical contrast at subwavelength spatial resolution (lambda /10) is achie ved using a fiber-based, infrared near-field microscope, at 3 mum wavelengt h. Chemically amplified polymer photoresists (poly(t-butylmethacrylate)), p atterned by ultraviolet radiation and 250 nm thick, are imaged using infrar ed (TR) wavelengths situated around the OH stretch band of the polymer, a r egion sensitive to photochemical changes associated with latent image forma tion. The key technical points that enable near-field infrared absorption m easurements down to 0.05% absorption sensitivity are discussed together wit h the major contrast mechanisms involved in image formation. The measuremen ts are complemented by confirming studies using confocal infrared microscop y and depth profiling. The exposure dose dependence of the acid catalyzed c hemistry, after the postexposure bake step, was studied on line/space patte rned samples. The OH subgroup absorption maps of the patterned polymer film exhibit features that are not present in the topographical changes (shrink age) induced by the postexposure polymer chemistry and illustrate significa nt potential of the IR near-field microscopy as an analytical tool for poly mer chemical physics. (C) 2001 American Vacuum Society.