Printing of Random Needle-like Resist Patterns Utilizing Laser Speckle Lithography

Abstract

Simple and low-cost optical lithography method utilizing speckles was researched for printing random patterns on wafer surfaces coated with thick resist films. Patterning characteristics were investigated using a handmade exposure system. In the system, a laser beam was irradiated on a transparent diffuser plate, and generated speckles were projected onto a wafer coated with 50-100 μm thick resist. As a result, the resist was sensitized, and patterns with random needle-like shapes were formed after development. Pattern sizes were between several microns and several hundred microns. The sizes and number of patterns were controllable by adjusting the exposure time. It was demonstrated also that the pattern sizes and the number of patterns were varied by changing the distance between the diffuser plate and the wafer. Maximum aspect ratios for various exposure conditions were also investigated. Although patterns were inclined or curved, very high aspect ratio of 14 was obtained for a 100-μm thick resist film.