Optimization methods for 3D lithography process utilizing DMD-based maskless grayscale photolithography system

Abstract

Digital Micromirror Device (DMD)-based grayscale lithography is a promising tool for three dimensional (3D) microstructuring of thick-film photoresist since it is a maskless process, provides possibility for the free-form of 3D microstructures, and therefore rapid and cost-effective microfabrication. However, process parameter determination lacks efficient optimization tool, and thus conventional look-up table (indicating the relationship between development depth and exposure dose value under a fixed development time) approach with manual try-and-error adjustment is still gold standard. In this paper, we firstly present a complete "input target-output parameters" single exposure optimization method for 3D microstructuring utilizing DMD-based grayscale lithography. This numerical optimization based on lithography simulation and sensitivity analysis can automatically optimize a combination of three process parameters for target microstructure; exposure dose pattern, a focal position, and development time. Through a series of experiments using a 20 µm thick positive photoresist, validity of the proposed optimization approach has been successfully verified. Secondly, with the purpose of further advancing accuracy and improve the uniformity of precision for the target area, a multiple exposure optimization method is proposed. The simulated results proved that the multiple exposure optimization method is a promising strategy to further improve precision for thicker photoresist structure.

Selective Surface Smoothening of Polymer Microlenses by Depth Confined Softening

“…show concave structures with 80 µm and 40 µm in a 58 µm thick ma‐P 1275G (micro resist technology GmbH, Berlin), optimized for exposure with direct DWL tools with λ = 405 nm light emitting diodes, as provided by the DWL66plus (Heidelberg Instruments), with an estimated tip radius of 5 µm. The 12.7 µm high pyramids presented by Ma et al featured even much sharper tips in positive resist (PMER P‐LA900PM, Tokyo Ohka Kogyo Co. Ltd) but at the same time had a root‐mean‐square (RMS) roughness of 0.8 µm.…”