# Uniform Pressing Mechanism in Large-Area Roll-to-Roll Nanoimprint Lithography Process
###### Abstract  
We aimed to increase the processing area of the roll-to-roll (R2R) nanoimprint lithography (NIL) process for high productivity, using a long roller. It is common for a long roller to have bending deformation, geometric errors and misalignment. This causes the non-uniformity of contact pressure between the rollers, which leads to defects such as non-uniform patterning. The non-uniformity of the contact pressure of the conventional R2R NIL system was investigated through finite element (FE) analysis and experiments in the conventional system. To solve the problem, a new large-area R2R NIL uniform pressing system with five multi-backup rollers was proposed and manufactured instead of the conventional system. As a preliminary experiment, the possibility of uniform contact pressure was confirmed by using only the pressure at both ends and one backup roller in the center. A more even contact pressure was achieved by using all five backup rollers and applying an appropriate pushing force to each backup roller. Machine learning techniques were applied to find the optimal combination of the pushing forces. In the conventional pressing process, it was confirmed that pressure deviation of the contact area occurred at a level of 44%; when the improved system was applied, pressure deviation dropped to 5%. roller bending; contact pressure; roll-to-roll process; nanoimprint lithography; high productivity 10.221119571. 11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11. The roller pushes a master roller and a flexible substrate passes between the two rollers. When the substrate passes, the pattern is imprinted continuously. The process is called roll-to-roll (R2R) imprinting [7; 8; 9; 10; 11]. This process has the advantage of improving productivity, but has a disadvantage of contact pressure non-uniformity. In general, the imprinting roller is brought close to the fixed pattern roller, and force is applied to both ends of this roller to generate imprinting pressure. Conventional R2R NIL systems inevitably cause the bending of the rollers in the pressing process, even if the roller's axial length is relatively short. When a roller deforms, it is difficult to make a uniform pattern in the NIL process. In general, R2R NIL requires a high imprinting pressure to minimize the residual layer thickness and allow the resin to completely fill the pattern in the mold [12]. The residual layer thickness becomes an important characteristic of an imprint pattern that requires a subsequent process such as etching, and if the residual layer thickness is not uniform, the following etching profile is not uniform. As a result, the non-uniform residual film thickness causes yield loss and cost increase [13; 14]. The precision of complex nano-sized patterns is demanding, and it is difficult to fill models with resin, especially for patterns with high aspect ratios without high imprinting pressure [12]. [PERSON] et al. studied pressure distribution in the nip between rubber-covered rollers in a paper transport system. A mathematical model and simulation tools were implemented to determine the effects of axial pressure variation and transverse bending on the pressure distribution. Numerical results showed that the bending of the roller caused significant non-uniformity in pressure distribution [15]. Attempts to increase the imprinting pressure in the conventional R2R imprint system caused a larger bending deformation of the imprinting roller and uneven pressure along the roller, resulting in pattern defects and non-uniform residual layer thickness. To solve this problem, it is necessary to improve the conventional R2R NIL system imprinting module. In addition, other causes have been reported for non-uniformity such as the deformation of the flexible material (skin) covering the roller, the roundness error of the roller and misalignment between the two rollers [16].