Asymmetric fluid-structure dynamics in nanoscale imprint lithography

across their diameter. These oscillations can be addressed by using a flat vacuumchuck with uniform pressure across the supporting surface.Figure 1.4c shows a wedged base layer that is due to angularmisalignment between the template and the wafer. The etch barrier is exposedwhen the template has an angle of inclination with respect to the wafer substrate.This occurs when the uncorrected misalignment between the opposing surfaces ofthe template and the transfer layer exceeds the motion capability of the flexurebasedtemplate stage. Figure 1.4d shows a thick base layer due to an excessivegap between the template and transfer layer during the exposure. The currentprocess to fill the gap is via squeeze film hydrodynamics and capillary action. Inorder for the etch barrier solution to fill the gap in a reasonable amount of time,the initial gap needs to be on the order of a few microns. If a 200 nm initial gap isused, the time-to-fill is very high [Choi, Johnson, and Sreenivasan, 1999]. Todeal with the two issues of minimizing the base layer thickness and the angle ofinclination of the base layer, an active stage system is under development to bettercontrol the filling and squeezing of the etch barrier base layers down to about 100nm prior to UV curing.(a) Thin, uniform base layer, desired(b) Wavy base layer(c) Wedged base layer(d) Thick base layerFigure 1.4 Base layer types13