Deposition of thin and uniform photoresist on three-dimensional structures using fast flow in spray coating

Realizing photolithography on three-dimensional structures is useful for micromachining; however, a thin and uniform resist film is difficult to prepare on a non-planar sample. A spray coating technique has the potential to deposit a uniform and defect-free resist film on a three-dimensional structure. In this study, the characteristics of spray coating are examined focusing on spray flow speed. Faster spray flow is found to remove the pinhole defects even at the bottom of a deep cavity with a high aspect ratio. The results of patterning performance on a deep three-dimensional structure are also shown. A line-and-space pattern on a 200 µm deep groove is demonstrated to have thick and thin resist coverage at the convex and concave corners, respectively with no pinhole defects. The obtained results of the spray coated resist film are discussed based on the fluid dynamics.