The underestimated impact of instabilities with nanoimprint

Abstract

With nanoimprint, instabilities of the polymeric layer between the substrate and the stamp are observed when incomplete filling of the stamp cavities prevails, resulting in capillary bridges and meandering structures. Experiments show that instabilities may also affect the initial situation of a thermal nanoimprint process. Already at the beginning of the actual imprint step, the polymeric surface may be highly non-uniform, with undulations of the film thickness, polymeric bridges and de-wetted regions; thus, the starting point for imprint may differ substantially from the general expectation of a uniform spin-coated layer. A detailed instability analysis considering the combined effect of van der Waals forces, electrostatic forces and temperature gradients under realistic imprint conditions clearly identifies temperature gradients to be the cause for high initial layer non-uniformities. We found that during heat-up (before imprint) temperature differences of 10 °C may exist between the top and bottom hotplate of a thermal imprint system. These temperature differences result in the non-uniformities of the polymeric layer observed, when stamp and sample are heated under low-pressure contact, where some small but locally arbitrary gaps exist between polymer and stamp. This result asks for a reconsideration of the thermal nanoimprint procedure. It also confirms the high impact of temperature control for uniform, low-defect imprint results; this is critical not only during imprint, but also during heat-up.