Computationally inexpensive simulations for nanoimprint lithography

Abstract

Among emerging nanopatterning techniques, nanoimprint lithography (NIL) is especially promising because the equipment required is relatively inexpensive. In NIL, a patterned template mechanically deforms a polymer film or resin on the surface of a semiconductor wafer (as shown in Figure 1) to transfer features and create an etching mask for subsequent processing. The prospect of reduced patterning costs enabled by this technique (compared with, for example, extreme-UV lithography) is particularly attractive to manufacturers of NAND flash memory, i.e., the predominant form of non-volatile memory used in electronic devices today. NAND flash memory does not require power to store data and is the key component of solidstate hard disk drives and camera memory cards. Nonetheless, to increase its adoption, it is crucial to reduce the cost per bit and, for this reason, there is an exceptionally strong incentive to reduce manufacturing costs. NIL is a promising approach for realizing a reduction in NAND flash manufacturing costs, but there are a number of associated challenges. For example, it is particularly difficult to achieve good inter-layer alignment and template lifetimes, and to minimize the pattern defectivity. Defectivity is the issue most in need of process modeling. There are two contributors to defectivity: random contributions (including particles or spatial errors in the dispensing of resin droplets onto the wafer); and systematic contributions, e.g., incomplete template-cavity filling, variation of the resin’s residual-layer thickness (between the template and the substrate), and template–resin adhesion. To ensure the successful use of NIL for fabricating NAND flash memory, it is necessary to predict any voids that may arise beneath the template after the dispensed droplets have spread Figure 1. Schematic illustration of nanoimprint lithography, using a droplet-dispensed resin.6 (1) A patterned quartz template is bowed and brought into contact with inkjet-dispensed pL-volume resin droplets on the wafer. (2) The curvature of the template is then relaxed to spread droplets and fill cavities. (3) After a dwell period (to enable residual layer homogenization), the resin is cured by UV exposure through the template.