Cold development of positive-tone resist ZEP520A (Nippon Zean) in electron-beam lithography needs quantitative analysis for further improvement in resolution. Contrast curves and groove widths in cold development of ZEP520A were analyzed using models, and resolution enhancement was confirmed experimentally. Although the contrast improved at the expense of sensitivity in cold development, the improvement of contrast became smaller when the development temperature became colder. The dependence of contrast curve on developing temperature can be explained assuming resist dissolution rates that have an activation energy. For resolution evaluation, circumferentially aligned line-and-space patterns were exposed using an electron-beam recorder with a rotary stage. The resolved groove widths were explained by using the resist dissolution model and an incident electron distribution that consists of three Gaussians. Using these models, groove widths after development can be easily calculated at arbitrary development and exposure conditions. The resolution improved in lower temperature, and dense line-and-space patterns of 35 nm pitch were resolved in −10 °C.

Reducing proximity effects is a key factor for achieving a higher resolution in electron-beam lithography and realizing the mastering of patterned media. The effect of substrate materials on backscattering electrons was investigated by simulation and experiment, and resolution enhancement was demonstrated. In Monte Carlo simulations with 100 keV incident electrons, the intensity of backscattering electrons decreased with decreasing atomic number of substrates. On the other hand, both the density of substrates and the existence of 10 nm thin films had negligible effects on the intensity of backscattering electrons. The measured exposure distributions from line-scanned electron beams supported the results of simulations. The intensity of backscattering electrons was reduced by using a carbon substrate, and circumferentially aligned high-density patterns of 878 Gbit/in.2 were resolved.

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