Fabrication technology of high-aspect-ratio pillar structures with positive sidewall angles using microlens-assisted photolithography

Abstract Micro-patterned chips used in digital PCR partitioning and fluidic bio-devices are typically manufactured through replication processes such as hot embossing with metal molds or injection molding, making them suitable for cost-effective mass production in industrial applications. During replication of such micro-patterns, the sidewall angle of the pattern geometry plays a critical role in determining replication fidelity. For high-aspect-ratio features, precise control of the sidewall angle becomes increasingly important. This paper presents a photolithography technique employing a microlens array (MLA) to fabricate master patterns for metal mold production. By controlling the exposure light path through microlenses, this method enables the formation of pillar structures with various inclination angles. Specifically, we demonstrate fabrication of pillar patterns with a positive sidewall angle of approximately 80°, and an aspect ratio of about 2, using a range of negative photoresists including SU-8, AZ-125nXT, and DNPR-4200.