Evaluation of Thick-Film Photoresist for Grayscale Lithography Utilizing Direct Laser Writing

Abstract

We report evaluation of thick-film positive photoresists for grayscale lithography. The target thickness of the photoresists is 10 to 20 µm, which is one the most popular range for micro structures. The precise direct laser writer, DWL 2000CE was utilized for the grayscale lithography. To evaluate the profile controllability of each photoresist by using dose correction, 256 grayscale slope pattern of 100 µm in length was fabricated on a glass substrate and measured by a confocal microscope. The dose correction realized liner relationship between grayscale value and residual thickness of the photoresists. By using an optimized data of the dose correction for each photoresist, 1024 grayscale microlens array pattern as a three-dimensional micro structure was successfully fabricated on a glass substrate. The fabrication error between the measured profile of one of the microlenses and the designed spherical profile of microlens of 80 µm in diameter and 16 µm in height was less than 0.2 µm within 10 µm from the center.