Planarization for reverse-tone step and flash imprint lithography

Understanding the dynamics of thin film planarization over topography is a key issue in the reverse-tone step and flash imprint lithography (SFIL-R) process. Complete planarization of a film over large, isolated topography poses an enormous challenge, since the driving force for planarization, the capillary pressure, continuously weakens as the film becomes more planar. For SFIL-R, only a specific degree of planarization (DOP) needs to be achieved before pattern transfer is possible. This paper presents the derivation of an inequality statement describing the required extent of planarization for successful pattern transfer. To observe how this critical DOP value (DOPcrit), and its corresponding leveling time (T-crit) vary with materials and topographic properties, finite difference simulation was utilized to model planarization of a thin film over isolated topography after the spincoating process. This model was verified experimentally for various film thickness to substrate height ratios using interferometry to monitor silicon oil planarization over isolated trenches and lines. Material and topographic parameters were shown to not have a dramatic impact on DOPcrit; however, the critical leveling time increased considerably at DOPcrit values above 60 percent.