Soft x-ray resist characterization: studies with a laser plasma x-ray source

Little work has been performed to characterize the exposure sensitivity, contrast, and tone of candidate resists for photon energies between 100-300 eV, the range in which projection soft x-ray lithography will be developed. We report here the characterization of near-edge x-ray absorption fine structure (NEXAFS) spectra, exposure sensitivity, contrast, and post-exposure processing of selected polysilane resists at photon energies close to the Si L2,3 absorption edge (100 eV). We find absorption resonance features in the NEXAFS spectra which we assign to excitation into Si-Si and Si-C *orbitals. Using monochromatized XUV exposures on the Si-Si cs* resonance at 105 eV, followed by solvent dissolution development, we have measured the exposure sensitivity curves of these resists. We find sensitivities in the range of 600-3000 mJ/cm2 and contrasts in the range from 0.5 - 1.4, depending on the polysilane side chain. We have also performed exposure sensitivity measurements at 92 eV, below the edge. Sensitivity decreases slightly compared to 105 eV exposures and the saturation depth and contrast both increase, as expected. We find also that exposing resist films to oxygen after XUV exposure, but before development, increases the sensitivity markedly.