Effects of exposure time on defects and demolding force in soft ultraviolet nanoimprint lithography

Based on a contact process, the ultraviolet (UV) nanoimprint process can overcome the linewidth limit of conventional photolithography caused by the diffraction effect. However, the contact between the mold and resist may introduce various defects to the two components. Some researchers have investigated the defects that emerge in the imprint process, such as particle contamination and curing shrinkage of the resist. However, the curing process of the resist itself should be studied because the curable resist is the carrier of the pattern transfer and the replication is accomplished by its shape remodeling. In this article, the authors focus on the effects of exposure time on the defects and demolding force in the soft UV imprint process. The replications are made by a soft polydimethylsiloxane mold under the same process parameters except that the curing time is different. Moreover, the curing degree of the resist and the value of the demolding force under various curing doses are measured. A mechanical model is established to analyze the behavior of the resist, which transitions from a liquid to solid stage by stage, and will help the authors to understand the above effects. By analyzing the relationships among the model of the resist, curing degree, demolding force, and resultant defects in the experiments, they propose a curing window, within which the curing time in the imprint process helps to remove defects in the shaped patterns and soft mold. Finally, using the optimized curing time, the best replicated patterns with 100 nm features are obtained.