Fluid and solid mechanics in the step and flash imprint lithography process
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Step and Flash Imprint Lithography (SFIL) has become a promising technology to bring integrated circuit feature sizes to the nanometer scale. It is a molding process in which liquid monomer is imprinted by a patterned template, with a UV cure to polymerize the monomer into its patterned form. The success of the process depends heavily on fluid management issues presented in this study. Important insights are obtained by detailed analysis of the physics of the fluid and solid mechanics, making it possible to manipulate issues including imprint time and pressure, template deformation, and feature filling in order to drive the process to becoming a successful and efficient manufacturing technique. The fluid mechanics are simulated using lubrication theory. The solid mechanics governing elastic deformation of the template are simulated using thin plate theory. The solution of this coupled fluid-solid mechanics problem provides a dynamic simulation of the elastic deformation of the template and the time evolution of the fluid flow and pressure. The interplay of elastic, viscous, and capillary forces govern the behavior of the fluid and solid mechanics. In order to avoid extreme viscous or capillary pressures that lead to elastic deformation, it is found that an exact balance of the viscous and capillary forces throughout the imprint yields negligible deformation. The imprint time can be reduced using multiple drops and apportioning drop volume appropriately. A study of feature filling in both the lateral and vertical directions is presented, and it is found that the aspect ratio and geometry of the feature determine its ability to fill. A vertical study of the fluid-air interface as it moves into a template feature provides new understanding of the mechanics of contact line motion and interface reconfiguration. A modified pressure boundary condition in the lubrication code handles fluid motion through template features in the lateral direction. Both studies determined that high aspect ratio features are more difficult to fill, either trapping air due to interface stretching or requiring a lag time before fluid moves into the feature. This study provides a better understanding of these fluid issues and presents insights into the details of the process that can be controlled to make the process a viable technology in the future of imprint lithography.