Asymmetric fluid-structure dynamics in nanoscale imprint lithography

Figure 6.13 shows the force-time plot for four different instances ofmotion supplied by the actuators. In all of the cases, the actuators move for about1 second. This translates into a higher average approach velocity. In Figure 6.13,the maximum force due to the squeeze film pressure increases when the approachvelocity is higher. The force increases proportionally with the approach velocity,but since the film thickness of each case is different, this increase in Figure 6.13is not linear.6.5 OBSERVATIONS AND DISCREPANCIES6.5.1 Particle ContaminationAlthough the experiments were performed in a class 100 clean-room,particle contamination was a fundamental problem in achieving the desired thinfluid layers of 100 – 200 nm. During the course of the experimental work, itbecame evident that is would not be possible to eliminate all particles without anautomated process. Particles could be caused by manual handling of theexperimental components. Furthermore, the fluid itself may have particles. Thewater was filtered using 0.02-micron filters. This resulted in slight improvementsin the minimum attainable gaps. The substrate was placed under a microscopewith a magnification of 100× to detect particles. This was done immediately afterthe substrate and template were cleaned in a solution of acetone followed by anisopropyl alcohol rinse and a filtered air bath. A comparison with a clean wafer,i.e. one that was not previously handled, showed that any handling beyond amoving the wafer from its container to the imprinting machine would result inparticle contamination.94