Enabling fast microfluidic chips fabrication: A practical guideline for microfluidics design and fabrication using photolithography for fast prototyping

Abstract

Microfluidics has emerged as one of the widely used technologies for drug testing, diagnostics, and biomedical applications. Photolithography fabrication process using SU-8-based photoresist is currently the most versatile technique for lab-scale chips prototyping. However, the gap between design stage and subsequent massive manufacturing often leads to failure of pushing chips into production. Here, we identify some of the key considerations that need to be evaluated during the design stage to avoid failures encountered in the manufacturing stage. Specifically, to ensure optimum alignment between layers, the bottom layer is recommended to be no smaller than 3 µm, while the top layer cannot exceed 500 µm due to image contrast limitation between layers. To reduce stress and delamination issues, it is recommended to remove unnecessary bulk crosslinked design because stress is mostly built within the crosslinked region. Additionally, feature corner needs to be designed as a curved smoothing shape rather than a sharp corner due to force imbalance during film shrinking or expanding. To achieve optimum resolutions, it is recommended to choose a suitable SU-8 product and process conditions. Lastly, multivariate analysis reveals a correlation between post-exposure bake, exposure and etching time, and film thickness. It is recommended to optimize these process conditions accordingly when film thickness and SU-8 materials are changed.