In this paper, the influence of the absorption shot noise on line edge roughness (LER) of photoresists for extreme ultraviolet (EUV) lithography is studied experimentally through the comparative analysis of LER obtained by EUV (92 eV photons) and 100 keV e-beam lithography. Techniques for performing EUV and e-beam lithography with a matched image log slope for a fair comparison of LER values are described. Measurements of absorption of 100 keV electrons estimated through a transmissive electron energy loss spectroscopy measurement with a 120 keV electron beam showed that despite having access to core levels in the material (e.g., 284 eV edge in carbon), these electrons mostly just excite the energy levels less than 100 eV in the resist, with a mean deposited energy of 35 eV. By combining the incident flux and the absorption probabilities, the absorbed quanta for patterning of 50 nm half-pitch line/space features was found to be similar between the two patterning technologies.
Despite achieving 15-nm half pitch, the progress in extreme ultraviolet chemically amplified resist has arguably decelerated in recent years. We show that this deceleration is consistent with approaching stochastic limits both in photon counts and material parameters.Contact hole printing is a crucial application for extreme ultraviolet lithography and is particularly challenged by resist sensitivity due to inherent inefficiencies in darkfield contact printing. Checkerboard strong phase shift masks have the potential to alleviate this problem through a 4× increase in optical efficiency. The feasibility of this method is demonstrated using the SEMATECH-Berkeley Microfield Exposure Tool pseudo phase shift mask configuration and preliminary results are provided on the fabrication of an etched multilayer checkerboard phase shift mask.
Progress in the ultimate performance of extreme ultraviolet resist has arguably decelerated in recent years suggesting an approach to stochastic limits both in photon counts and material parameters. Here we report on the performance of a variety of leading extreme ultraviolet resist both with and without chemical amplification. The measured performance is compared to stochastic modeling results using the Multivariate Poisson Propagation Model. The results show that the best materials are indeed nearing modeled performance limits.
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