Optimizing Filling of Anisotropic Templates inUV Nanoimprint Lithography
Yang H. Ban and Roger T. Bonnecaze *McKetta Department of Chemical Engineering, The University of Texas at Austin,Austin, Texas 78712, United States
E-mail: harinban@utexas.edu

Abstract:
A key to the successful deployment of UV nanoimprint lithography (UV-NIL) tointegrated circuit (IC) manufacturing will need to break the bottleneck of UVNIL. There areseveral experimental observations and analysis which indicates template fluid filling, thebottleneck, is strongly related to the structure of a template and the configuration of droplet
placement. Therefore, through the insights gained from a comprehensive model which
captures major physics involved with fluid flow, rational design of a template or a droplet
pattern could be employed in the future to achieve a low defectivity and high throughput
UVNIL process. Thus, our research problem is finding an optimal UVNIL process setting
which run at the shortest fluid filling time that leads to an acceptable defect density.
From experimental observations, it is found that the optimized droplet placement cansignificantly reduce defect density while not compromising the throughput of UVNIL. The
challenge is to optimally place the droplets on the substrate under the template. This isparticularly challenging for anisotropic templates, such as lines and spaces, where the filling
process is highly directional. Currently, these optimized droplet placement is found by trialand error which is expensive and laborious. Our ultimate research goal is development ofcomputer simulations which is a faster and inexpensive means to find optimizing droplet
placements.
Simulation of UVNIL using a template with line and space patterns with nine droplets
dispensed in a square arrangement is shown in Fig. 1. It was founded that the droplets arestretched when UVNIL is carried out with templates having line and space patterns. The noncircular shape is a result of the difference in flow permeability in x and y directions 1. The
higher permeability in y-direction compare to x-direction leads to the droplet spreading fasterin the y-direction compared to the x-direction and forming straight channels (Fig. 1).
However, the simulation result shown in Fig. 1 is not completely satisfactory because straightchannels of unfilled regions was not observed in simulation. We believe the discrepancy
exists between the experimental result and simulation can be mitigated by considering moreaccurate capillary pressure boundary condition.
Here we present a theory and simulation for fluid filling for anisotropic templates.
The theory includes an anisotropic permeability to account for the variation in flow resistanceparallel to the template. It also includes a varying capillary pressure (Fig. 2) that depends on
the position of the gas-liquid interface relative to the orientation of the template. This theory
is integrated into a simulation of template filling and droplet motion and merging for up to
1000 droplets to optimize droplet positions under different anisotropic templates.
Reference:[1] Jain, A.; Spann, A.; Cochrane, A.; Schunk, P. R.; Bonnecaze, R. T., Fluid flow in UV
nanoimprint lithography with patterned templates. Microelectronic Engineering 2017, 173,
62-70.

Figure 1. Fluid spreading with a patterned template with vertical grating. In experiment, straightchannels of fluid and unfilled cavity formed (left figure). Simulation result also shows ananisotropic flow (right figure), qualitatively similar to the experimental result1

Figure 2. Capillary pressure calculated under various configuration created by vertical grating
template. The comment next to legend present the range of height where stable interface existed inSurface Evolver simulation.