Effects of resist thickness and viscoelasticity on the cavity filling capability in bilayer thermal embossing

Poly(methyl methacrylate) (PMMA) bilayer structures are employed as resists to investigate deformation of polymers by microthermal embossing. Owing to the dispersion of Fe₃O₄ particles in the upper layer, the distinct interface profiles of each layer resist can be observed by scanning electronic microscope (SEM). Deformation and replication fidelity are attributed to a variety of factors in the imprinting process. In particular, the thickness of each resist layer and the viscoelasticity of different molecular weight polymers play the most crucial roles among these factors. Based on experimental results, we improved the deformation models of imprinting for bilayer PMMA material and evaluated the models via specific parameters: the degree of deformation of the lower layer (D_L), the fraction of cavity filling of the lower layer (F_L), and variation in the fraction of the upper layer thickness (K_i). The final pattern of the upper or lower layer may be implicated in micro electro mechanical systems (MEMS).