SFIL Process

Step and Flash Imprint Lithography (SFIL) uses photopolymerization of an organosilicon solution through a rigid transparent imprint template to define the pattern topography on a substrate. The use of a low-viscosity UV curing solution allows imprinting at room temperature with minimal applied pressure. Typically the imprinting process is performed over a blanket layer of organic polymer, creating a bilayer structure. This removes the need to imprint high aspect ratio features, since the pattern aspect ratio can be subsequently amplified by dry etching. The use of a rigid transparent imprint template allows flood exposure of the photopolymer to achieve cure, and enables classical optical techniques commonly used in mask aligners, photolithography steppers, and scanners for layer-to-layer alignment. Details of the SFIL process are shown in Figure 1, and includes the following steps.
  • An organic polymer layer (transfer layer) is spin-coated on a substrate, typically silicon.
  • A low viscosity, photopolymerizable, organosilicon solution (etch barrier) is then dispensed on the wafer in the area to be imprinted.
  • A transparent template bearing patterned relief structures is aligned over the coated silicon substrate.
  • The template is lowered onto the substrate, displacing the etch barrier that fills the imprint field and trapping the etch barrier solution in the template relief. Irradiation with UV light through the backside of the template cures the etch barrier into a crosslinked polymer film. A fluorocarbon release layer on the template allows separation from the substrate, leaving an organosilicon relief image that is a replica of the template pattern.
  • A halogen etch is used to break through the undisplaced etch barrier material (residual layer) exposing the underlying transfer layer.
  • An oxygen reactive ion etch (RIE) is used to transfer the image through the transfer layer thereby amplifying the aspect ratio of the imprinted image.
Figure 1. SFIL process flow. The process employs a template/substrate alignment scheme to bring a rigid template and substrate into parallelism (a), trapping the etch barrier (b). The gap is closed until the force that ensures a thin base layer is reached. The imprint is then illuminated through the backside of the template (c) to cure the etch barrier. The template is withdrawn (d), leaving low-aspect ratio, high resolution features in the etch barrier. The residual etch barrier (base layer) is etched away with a short halogen plasma etch, after which the pattern is transferred into the transfer layer with an anisotropic oxygen reactive ion etch (e), creating high-aspect ratio, high resolution polymer features.