UV-curable nanoimprint resist with liquid volume-expanding monomers

For ultraviolet nanoimprint lithography (UV-NIL), the resist volume shrinkage during curing not only influences the pattern fidelity but also induces defects in the demolding process due to strong adhesion. To address this issue, a novel nanoimprint resist was formulated and characterized in this work. The new resist formulation contains 3,9-diethyl- 3,9-bis(allyloxymethyl)-1,5,7,11- tetraoxastetraoxaspiro [5] undecane (DB-TOSU), which is a liquid spiroorthocarbonate monomer that undergoes volume expansion upon acid-catalyzed polymerization. By mixing DB-TOSU with conventional volume-shrinking epoxy monomers at various weight ratios, the formulated resists had much reduced or even zero volume shrinkage. The resist volume shrinkage, elastic modulus, and demolding force decreased with increasing DB-TOSU weight ratio in resist formulation. When DB-TOSU reached 50 wt%, the demolding force was reduced by 69% with an adequate elastic modulus (75 MPa) and low shrinkage (1.86%). This novel resist formulation has the potential to allow high-fidelity pattern replication and reduce demolding defects in UV-NIL.