Thermal Modeling of Ultraviolet Nanoimprint Lithography

Nanoimprint lithography (NIL) is a promising nanomanufacturing technology that offers an alternative to traditional photolithography for manufacturing next-generation semiconductor devices. This technology involves coating an ultraviolet (UV)-curable monomer layer on the substrate and then imprinting it with a template containing topography corresponding to the desired substrate features. While the template is close to contact with the substrate, the monomer is cured by UV exposure. This results in definition of desired features on the substrate. While NIL has the potential of defining very small feature sizes, thermal management of this process is critical for ensuring accuracy. Heat generation in the monomer layer due to UV absorption needs to be managed and dissipated in order to avoid thermal expansion mismatch and consequent misalignment between the template and wafer. In addition, thermal dissipation must occur in a timeframe that does not adversely affect the required lithography throughout. This paper develops a numerical simulation model of the nanoimprinting process and utilizes the model to study the effect of various geometrical parameters on the accuracy and throughput of the process. The effect of the UV power characteristics on heat dissipation and consequently on misalignment due to thermal expansion is studied. Results indicate that the thermal expansion mismatch due to commonly used UV exposure parameters may be minimized by utilizing a lower exposure power for longer time. A transient model enables a study of the effect of die imprint sequencing on the overall temperature rise during the process. Results indicate a critical trade-off between minimizing temperature rise on one hand, and maximizing system-level throughput on the other. By identifying and quantifying this trade-off, this work contributes to development of error-free nanoimprint lithography for future technology nodes.