Technique for preparing defect-free spray coated resist film on three-dimensional micro-electromechanical systems

Microstructures with high aspect ratio have been fabricated in micro-electromechanical systems (MEMS). The fundamental structures are relatively simple, since the fabrication process relies on planar photolithography. Spray coating of the photoresist is expected to become a new photolithography method for realizing real three-dimensional microstructures. However, as-deposited resist films have pinholes, particularly in the deep regions. This poses limitations to photolithography. Therefore, a new technique is introduced for removing pinholes by means of the migration of resist material on sample surfaces. Thinner vapor assists the migration of resist, generating the driving force of surface tension. The resist material accumulates in the regions with high pinhole density. Consequently, the pinholes are filled efficiently. This effect comes at the cost of thinning the resist coverage in convex corners of a cavity. The removal of pinholes and the decrease of resist film coverage at convex corners may be balanced.