Optimal placement of droplets for UV nanoimprint lithography

Abstract

Optimizing the locations and sizes of droplets are key to reduce defects and increase throughput of ultraviolet nanoimprint lithography (UVNIL). Previously, simulation models describing the flow and coalescence of multiple fluid drops were developed and used to predict the fluid flow during spreading and feature filling. However, the effect of small channels on the resulting capillary pressure is neglected even though the flow along small channels or grooves is encountered in UVNIL. In this study, an accurate method to estimate capillary pressure boundary conditions at the fluid-air interface is developed along with fluid simulation. A method to estimate and compute the anisotropic capillary pressure for templates with line and space patterns is presented. It is found that the droplets flow faster in the direction of the pattern not only because of anisotropic permeability but also the nanostructure of the template, which further propels anisotropic spreading of the droplets by exerting larger capillary pressure. Using the new capillary pressure boundary condition, the simulation of multidrop spreading in UVNIL is performed to study the effects of anisotropic capillary pressures caused by the template structure. A simulation approach to determine optimal droplet placement was developed. From the simulation, a general rule of thumb is developed: delaying droplet merging as much as possible and reducing the number of merging events.