Typically, a negative-type photoresist consists of a polymer binder, polyfunctional monomer (or cross-linker), photo initiator, solvent, and additives. A series of acrylic monomers was prepared as cross-linkers using dipentaerythritol hexa-acrylate (DPHA) and blending monomers with n-butyl methacrylate (BuMA), benzyl methacrylate (BzMA), and acrylic-silica sol (Pro-1264), and the mechanical properties of patterns were studied. The elastic recovery and the compression of the patterns were measured using a dynamic ultra-micro-hardness tester. Patterns of the photo spacer were observed using a scanning electron microscope. Superior mechanical properties (elastic recovery, compression, and surface hardness) of the patterns and the optimum recipe could be obtained by adding 2wt% of acrylic monomers (BuMA or BzMA or Pro-1264) to the photoresists when DPHA was fixed at 10wt%. An inverted conical pattern was observed when 3wt% of Pro-1264 was added to the photoresists when the transmittance of patterns worsened because of the low capacity of the interpenetration network.
