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Second generation proximity x-ray lithography (PXL-II), which uses shorter incident x-ray wavelengths and resist materials, is expected to be a candidate for next generation lithography. In the PXL-II technique, the x-ray wavelength absorbed in the resist becomes shorter, but degradation of the pattern quality due to secondary electron blur has not been sufficiently evaluated. In this article, we present our investigation of the secondary electron blur’s suppression in Br-containing resist using a lithographic simulator and a Monte Carlo simulator for electron scattering. By introducing the Br element into resist materials, the electron stopping power improves. In addition, secondary electron blur is suppressed in regions with wavelengths shorter than that of the Br absorption edge. In order to evaluate pattern resolution, the image contrast of the lateral absorbed image in the resist is defined. We found that image contrast is improved in Br-containing resist for the wavelength range down to about 4.5 Å, which is suitable for PXL-II. We also show that it should be possible to extend PXL-II for resolutions of less than 40 nm at a narrower gap.

Most of positive chemical amplification resists do not have enough stability to process delay. It has been claimed that airborne contaminants neutralize acids from photo-acid generators. It has been found by means of X-ray photoelectron spectroscopy that an onium salt used as a photo-acid generator is deficient at the surface of the prebaked resist film. The over-top coating using water-soluble polymers with organic acids has been investigated in order to not only separate the resist surface from airborne contaminants but also supply acids to the resist surface. We have succeeded in the suppression of the surface insoluble layer generation and of the pattern size change for more than 8 hours.

A new method is proposed to evaluate the acid diffusibility in a chemical amplification resist using acidic overcoat film. This method is easy and effective for both positive- and negative-tone resists and is not influenced by the uncertainty in optical images. The acid diffusion coefficient was estimated for various process conditions. The acid loss reaction was introduced in Fick's law, and the calculation showed a good agreement with experimental results. In order to obtain good profile patterns with sufficient controllability, the distribution of acids in the resist must be controlled as well as diffusion length. The resist patterns replicated using X-ray lithography corresponded to those expected from experimental results.