Resolution Enhancement of Hole Patterns in Sychrotron Radiation Lithography

This paper analyzes the influence of Fresnel diffraction on the patterning characteristics of isolated hole patterns in synchrotron radiation lithography by comparing Fresnel diffraction simulation extended to 2-dimensional patterns and pattern replication experiments with mask contrast as a parameter. It is possible to replicate hole patterns down to 0.1 µm at a large proximity gap of 30 µm by keeping the mask contrast at 2.5-7. However, the exposure latitude for fine patterns below 0.1 µm diminishes abruptly. It also becomes clear that the phase-shifting mask which we previously proposed offers the possibility of replicating ultra-fine hole patterns (<0.1 µm) with a large exposure latitude at the 30-µm proximity gap. Moreover, by using an X-ray mask with a circular absorber pattern instead of the conventional square pattern, it should be possible to solve the problem of pattern deformation and improve the exposure latitude.