Effects of Mold Side Wall Profile on Demolding Characteristics

Silicon molds with various taper angles are fabricated and demolding forces are examined for the thermal imprinting of poly(methyl methacrylate) (PMMA) films on a silicon substrate. The silicon mold patterns are fabricated by a switching process, which consists of sequentially alternating etching and deposition steps. The side wall angle of mold trenches is controlled by adjusting deposition step time. The demolding force for the vertical mold is 0.35 MPa. The demolding forces for the inverse taper mold angle (taper angle, 92°) and the normal taper angle (taper angle, 83°) are 1.0 and 0.2 MPa, respectively. The residual PMMA thickness is not uniform. The surface profile of the PMMA film is also curved. Both the nonuniform residual PMMA thickness and the curved profile of the PMMA surface are caused by silicon wafer deformation. It is confirmed that the variation of PMMA surface height is proportional to the residual resist thickness.