Volume-expansion polymerization for UV-curable nanoimprinting

Abstract

In ultraviolet (UV) nanoimprinting, polymerization of liquid monomers is generally accompanied by a decrease in the resist volume, which often causes problems such as residual stress, pattern distortion, and replication defects. Thus, it is highly desirable to reduce or even eliminate volume shrinkage during monomer polymerization in UV nanoimprinting. To achieve this goal, monomers that undergo volume expansion during polymerization are added into the resist formulation. Spiro-orthocarbonate is a monomer that expands upon cationic ring-opening polymerization. By mixing the spiro-orthocarbonate monomer with a common epoxy monomer, the authors achieved a zero volume change after curing. It is also possible to achieve volume expansion in this new resist formulation. The residual stress in the cured resist structures is also effectively mitigated. It is expected that elimination of volume shrinkage in UV nanoimprinting can address important issues such as pattern fidelity and high demolding forces.