Asymmetric fluid-structure dynamics in nanoscale imprint lithography

an overlay scheme in multi-layered circuits. High temperatures and pressure canlead to technical difficulties in accurate overlay for multi-layered circuits.SFIL uses no projection optics and, as with other imprint processes, onecould best describe SFIL as a micro-molding process. The traditional photomaskhas been replaced by a topographical template, which contains the circuit patterngenerated by direct write E-beam lithography. The template acts as the masterpattern for the etch barrier layer. The key difference between SFIL and otherimprint lithography techniques is the use of the liquid etch barrier layer. The etchbarrier layer is a low viscosity, photopolymerizable formulation containingorganosilicon precursors [Colburn et al 1999]. This low viscosity eliminates theneed for high temperatures and pressures to achieve the thin films desired forpatterning. Figure 1.2 illustrates the SFIL process.(Step 1) First, an organic transfer layer is spin-coated on a silicon wafer.This transfer layer adheres to both the silicon wafer and etch barrier layer andfunctions as a planarization layer during imprinting while providing high etch rateselectivity during the device etch step. (Step 2) Next, a quartz template bearingthe relief image of the circuit is brought into proximity of the transfer layer andwafer. The template must be easily wetted by the etch barrier solution, and itmust easily release the polymerized etch barrier once it has been exposed. Inorder to fulfill these requirements, the template is treated with a release layer tomodify its surface chemistry. (Step 3) Once the template is brought near thewafer, a micro-fluidic dispensing system dispenses a specific pattern of thephotopolymerizable, organosilicon etch barrier fluid. The fluid the fills the gapbetween the template and transfer layer via a squeeze film effect and capillaryaction.9