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

Abstract

Scanning transmission x-ray microscopy (STXM) is shown to be a powerful imaging technique that provides chemical selectivity and high spatial resolution (∼35nm) for studying chemically amplified photoresists. Samples of poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line∕space pattern of 1.10μm∕0.87μm 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.

Electron-beam exposure mechanisms in hydrogen silsesquioxane investigated by vibrational spectroscopy and in situ electron-beam-induced desorption

“…This result is consistent with previous observations of HSQ baking via FTIR. [19][20] The large peak at ~2256 cm -1 is present in both Raman and FTIR and has been identified as the "stretching"…”

Scanning x-ray microscopy investigations into the electron-beam exposure mechanism of hydrogen silsesquioxane resists

“…16 Briefly, synchrotron-generated soft x-rays are monochromated and focused to a diffraction-limited spot (in this case 35 nm FWHM) by a Fresnel zone plate. Images are obtained by measuring the intensity of the transmitted x-rays as the HSQ sample is raster-scanned through the focused beam.…”

“…15 Recently, scanning transmission x-ray microscopy (STXM) was used to investigate the spatial distribution of the deprotection reaction occurring in a typical chemically amplified resist. 16 This analysis technique measures the reaction zone with chemical specificity and high spatial resolution (~35 nm). In this paper, we employ the same STXM techniques in combination with AFM studies of the e-beam exposed latent image to elucidate the details of the chemistry and possible area dependence of the sensitivity that occurs during electron-beam exposure of HSQ.…”

Quantifying reaction spread and x-ray exposure sensitivity in hydrogen silsesquioxane latent resist patterns with x-ray spectromicroscopy

“…12,15,33,34 To address questions pertaining solely to the exposure-induced chemical changes, undeveloped ͑latent͒ photoresist patterns can be imaged at high spatial resolution ͑ϳ30 nm͒ with scanning transmission x-ray microscopy ͑STXM͒. 16,35 Differences in bonding structure around the Si and O atoms in HSQ before and after cross-linking are measured using near edge x-ray absorption fine structure ͑NEXAFS͒ spectroscopy. These changes in bonding reflect the degree of cross-linking in the exposed versus unexposed regions of the HSQ film prior to development.…”