Investigation of the Photoresist Pattern Profile Contrast Improvement in Interference Lithography Technique Using 488-nm Laser

The interference lithography technique at 488 nm is explored theoretically and experimentally, and the effect of photoresist pattern profile contrast improvement is presented. In order to produce high contrast photoresist patterns using interference lithography, the system setup and process have to be optimized strictly, and process optimization can be facilitated by simulation. In the proposed simulation method, the absorption coefficient of photoresist varying with wavelength is considered by using photoresists with lower absorption coefficients, or, for the same photoresist, using laser sources with longer wavelengths. The visibility of aerial fringe patterns of the photoresist can be improved greatly. However, after developing, the contrast of photoresist patterns was not improved. The reason is that the photo sensitivity and etching rate V of photoresist decrease at 488 nm. This offsets the effect of lower absorption coefficients even though a 488-nm argon ion laser source is useable for some photoresists. This opens up a new window for the interference lithography technique.