Chemical mapping of polymer photoresists by scanning transmission x-ray microscopy

Scanning transmission x-ray microscopy (STXM) is shown to be a powerful imaging technique that provides chemical selectivity and high spatial resolution (∼35 nm) for studying chemically amplified photoresists. Samples of poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a linespace pattern of 1.10 μm0.87 μm followed by a post-exposure bake, are used to demonstrate STXM imaging capabilities to extract photoresist latent images. Chemical contrast is obtained by measuring the x-ray absorption at an energy of 290.5 eV, corresponding to a carbon K shell electronic transition to the unoccupied π* molecular orbital of the PTBOCST carbonyl group. A quantitative analysis provides the spatial distribution of the fraction of the unexposed and deprotected polymers remaining after the post-exposure bake stage as well as the thickness of both regions. Both chemical and topographical contributions to the total contrast are estimated. Advantages and limitations of STXM in comparison with other imaging techniques with chemical specificity are discussed. © 2005 American Vacuum Society.