Reverse-tone step and flash imprint lithography (SFIL-R)shows promise as a cost-efficient, high-resolution patterning technique; however, the generation of satisfactory patterns requires the successful application of a planarizing topcoat over topography through spincoating. Photopolymerizable nonvolatile fluids are ideal topcoat materials because they planarize better than volatile fluids during spincoating and can continue to level after spincoating. Fluid mechanics analyses indicate that complete planarization using capillary force is slow. Therefore, defining the acceptable or critical degree of planarization (DOPcrit) becomesnecessary. Finite difference simulation of the spincoat and postspinleveling processes was used to determine the planarization time forvarious topographic and material property combinations. A new material, Si-14, was designed to have ideal planarization characteristics (low viscosity—15.1 cP; low shrinkage—5.1%) and satisfy SFIL-R processing requirements (oxygen etch resistance—33 wt% silicon, photocurable) and was used to validate our models through profilometry and interferometry experiments. During spincoating, minimizing the spin speed generates more planar films; however, this increases the spin time. To rectify this problem, a two-stage spincoating process—a first step with high spin speeds to achieve the target thickness quickly and a second step with low spin speeds to improve planarization—was proposed and experimentallydemonstrated.