Impact of polymer film thickness and cavity size on polymer flow during embossing: toward process design rules for nanoimprint lithography

Abstract

This paper presents continuum simulations of polymer flow during nanoimprint lithography (NIL). The simulations capture the underlying physics of polymer flow from the nanometer to millimeter length scale and examine geometry and thermophysical process quantities affecting cavity filling. Variations in embossing tool geometry and polymer film thickness during viscous flow distinguish different flow driving mechanisms. Three parameters can predict polymer deformation mode: cavity width to polymer thickness ratio, polymer supply ratio and capillary number. The ratio of cavity width to initial polymer film thickness determines vertically or laterally dominant deformation. The ratio of indenter width to residual film thickness measures polymer supply beneath the indenter which determines Stokes or squeeze flow. The local geometry ratios can predict a fill time based on laminar flow between plates, Stokes flow, or squeeze flow. A characteristic NIL capillary number based on geometry-dependent fill time distinguishes between capillary- or viscous-driven flows. The three parameters predict filling modes observed in published studies of NIL deformation over nanometer to millimeter length scales. The work seeks to establish process design rules for NIL and to provide tools for the rational design of NIL master templates, resist polymers and process parameters.

Confinement and flow dynamics in thin polymer films for nanoimprint lithography

“…[10][11][12][13][14] On the other hand, confinement will also directly impact the flow pattern. This parameter is prominent in a number of numerical studies of embossing 15,16 but there is still a good deal of confusion over this issue. On the one hand, some studies of NIL reflow 17,18 completely neglect the direct impact of confinement on flow rate.…”

“…It may be used for flow rate assessment both for structure stability against reflow and for material flow into the structures during embossing or to identify dominant flow modes. 16 In another area, it may also be of use for the assessment of the rheological properties of very thin polymeric films per se.…”

Legitimate domain of a Newtonian behavior for thermal nanoimprint lithography

“…In particular for an imprint temperature close to the glass transition temperature, both experiments [4] and simulations [5] have shown that the elastic effects are predominant. In other cases, shear-thinning can be used [6] as a first step of equations simplification, but this requires to solve non-linear systems.Thus, in a more restricted set of cases, the Newtonian behavior has been used as a cheap and efficient way to predict the polymer flow in micro and nano size cavities. This behavior has shown a remarkable capability to simulate the reflow of nano size structures to measure the viscosity in sub-micrometer polymeric films [7,8].…”

Achieving nanoscale horizontal separations in the standard 2 μm PolyMUMPS process

“…Processes with horizontal nanoseparations may use electron beam lithography (EBL) (Henini 1999) or nanoinjection lithography (NIL) (Rowland et al 2005), for example to attain the required resolution. However, both techniques require equipment that may not always be available in academic institutions or small companies.…”