Polymerization Shrinkage and Adhesion in UV-Nanoimprint Lithography

Ultraviolet nanoimprint lithography (UV-NIL) is a molding-based nanofabrication technique utilizing the change in viscosity of a UV resist upon UV irradiation and is one of the most promising candidates for mass-production lithography [1]. The biggest challenge, however, in UV-NIL is demolding, a process to remove the stamp from the molded substrate. Numerous efforts have been made to make the demolding process easier with the main goal being the reduction in adhesion at the stamp/resist interface. However, it is not only the adhesion at the stamp/resist interface that produces stress during demolding. The force applied to the sidewalls of stamp structures by resist shrinkage occurring during UV curing also contributes to demolding force. Experimental methods such as bilayer beam deflection [2] have been employed to measure stress generated in a thin resist layer during UV curing. However, the stress measured by these methods does not represent the real UV-NIL process in which the resist is locally confined within the stamp structures. To the best of our knowledge, there has been no attempt to experimentally determine the stress by polymerization shrinkage in the actual UV-NIL system.