Resolution-limiting factors in low-energy electron-beam proximity projection lithography: Mask, projection, and resist process

摘要

The resolution-limiting factors in low-energy electron-beam proximity projection lithography were analyzed quantitatively using the blur of a Gaussian-shaped latent image (σ_(QBP)) as the resolution index. σ_(QBP) is the square root of the sum of squares of the factors, such as electron scattering and resolution performance of resist. The resolution limit of 45 nm for isolated patterns and the resolution of 70 nm for practically used periodic patterns with 10% exposure latitude were achieved at σ_(QBP) of 49 nm. Eliminating a crossover in the electron optics decreased the factor depending on the gap between a mask and a wafer to 19 nm at a 40 μm gap. Because of the intensive studies on multilayer processes, the factor attributed to the resolution performance of thin resist dropped from 58 to 26 nm. Reduction in the blur due to electron scattering, 34 nm in the case of a 70-nm-thick resist film and 2 keV electrons, must be considered for the 45 nm technology node.