Effect of droplet size, droplet placement, and gas dissolution on throughput and defect rate in UV nanoimprint lithography

Simulation of multidrop spreading in ultraviolet nanoimprint lithography is performed to study the effects of droplet size, droplet arrangement, droplet placement error, and gas diffusion on filling-time and defects. Simulations are carried out for square, hexagonal, and modified hexagonal arrangements of up to 1024 droplets ink-jetted on a substrate to determine the optimum arrangement for minimum imprint time. The effect of error in droplet placement by the inkjet dispenser on the imprint time for different droplet sizes is also investigated. The square droplet arrangement leads to the shortest fluid filling time for a flat template. The filling time increases significantly for droplet placement errors of more than 0.01% relative to the width of the substrate. A model is presented to study the diffusion of gas encapsulated between droplets into the resist. A dimensionless parameter alpha similar to mu D/k(H)gamma H-o measures the relative importance gas diffusion to hydrodynamics, where D is the gas diffusion constant, k(H) is the Henry's law constant, mu is the resist viscosity, and gamma is the surface tension of the imprint resist. For small values of alpha, gas diffusion is slower than resist spreading and defect size is diffusion-controlled while for larger values, gas diffusion is faster than resist spreading and the defect size is hydrodynamically controlled. Scaling laws are developed to extrapolate predictions on filling time, residual layer thickness, and defects here for hundreds to a thousand droplets to tens and hundreds of thousands of droplets. (C) 2016 American Vacuum Society.