Simulation of fluid flow in the step and flash imprint lithography process

Abstract

Step and Flash Imprint Lithography (SFIL) is a photolithography process in which the photoresist is dispensed onto the wafer in its liquid monomer form and then imprinted and cured into a desired pattern instead of using traditional optic systems. The mask used in the SFIL process is a template of the desired features that is made using electron beam writing. Several variable sized drops of monomer are dispensed onto the wafer for imprinting. The base layer thickness at the end of the imprinting process is typically about 50 nm, with an approximate imprint area of one square inch. This disparate length scale allows simulation of the fluid movement through the template-wafer channel by solving governing fluid equations that are simplified by lubrication theory. Capillary forces are also an important factor governing fluid movement; a dimensionless number known as the capillary number is used to describe these forces. This paper presents a simulation to model the flow and coalescence of the multiple fluid drops and the effect the number of drops dispensed has on final imprint time. The imprint time is shown to decrease with the use of increasing numbers of drops or with the use of an applied force on the template. Appropriate filling of features in the template is an important issue in SFIL, so a mechanism for handling the interface movement into features using a modified boundary condition is outlined and examples are. Fluid spreading outside of the mask edge is also an issue that is resolved by results from this study. The simulation is thus a useful predictive tool providing insight on the effect multiple drop configurations and applied force have on imprint time, as well as providing a means for predicting feature filling.