Molecular dynamics study of pattern transfer in nanoimprint lithography

Abstract

A molecular dynamics simulations model of nanoimprint lithography (NIL) is proposed in order to study the pattern transfer and its related phenomena. The proposed model is similar to a real NIL process imprinting an a-quartz stamp with a rectangular line pattern into an amorphous poly-(methylmethacrylate) (PMMA) film. The polymer deformation behavior and the adhesion and friction effects between the stamp and the polymer film are investigated and their dependency on the pattern aspect ratio is discussed. Force fields including bond, angle, torsion, van der Waals, and electrostatic potentials are used to describe intermolecular and intramolecular interacting forces. Nose´-Hoover thermostat is used to control the temperature of the polymer film and cell multipole method is adopted to treat long range interactions. The deformation of the polymer film is observed for two stamps having different aspect ratio patterns. The distributions of density and stress in the polymer film are calculated for the detail analysis of deformation behavior. For a high aspect ratio pattern (aspect ratio = 2.5, imprint depth = 8.0 nm), large amount of springback of the residual polymer film is observed, which is mainly due to the residual compressive stress left in the polymer film. However, for a low aspect ratio pattern (aspect ratio = 1.0, imprint depth = 3.0 nm), the springback is not observed. In addition, adhesion and friction forces are obtained by dividing the polymer film into subregions and calculating the interacting force between each subregion and the stamp. While the adhesion force is nearly constant regardless of the pattern aspect ratio, the friction force increases as the pattern aspect ratio grows, so the friction force becomes larger than the adhesion force when the pattern aspect ratio increases.

Simulation and Mitigation of Pattern and Process Dependencies in Nanoimprint Lithography

“…Growing effort is therefore being applied to molecular dynamics simulations of NIL [33], [34]. For an assumed imprinting temperature, required imprinting forces have been predicted by simulation [34].…”

“…For an assumed imprinting temperature, required imprinting forces have been predicted by simulation [34]. Furthermore, such simulations have enabled stamp-resist adhesion and friction to be studied as functions of the depth-to-width aspect ratio of imprinted features: sidewall friction is found to become dominant with increasing aspect ratio [33]. More recent simulations have explored the dependence of the required imprinting force on the resist's molecular weight, on the feature's diameter, and on the stamp's sidewall roughness [35].…”

Crystallographic orientation-dependent pattern replication in direct imprint of aluminum nanostructures

“…However, little information about the influence of crystallographic orientation on direct imprint process is known. Moreover, although molecular dynamics (MD) simulation has been widely utilized to explore nanoimprint processes [16][17][18][19], there is limited work that evaluates the properties of patterned structures.…”

“…The silicon master is treated as a rigid body throughout the direct imprint process. The atomic interactions in the Al substrate and that between the Al substrate and the Si master are molded by embedded atom method and Lennard-Jones potential, respectively [19]. The Si master is initially placed above the substrate surface with a distance of 1.2 nm.…”

Molecular Dynamics Study of Line Edge Roughness and the Proximity Effect in Electron Beam Lithography

“…Stochastic simulations reveal the microscopic material and process effects on pattern formation in photolithography, extreme ultraviolet lithography, and electron beam lithography (EBL). Molecular dynamics (MD) simulations are also a powerful tool to investigate nanometer-scale patterning, and MD simulations have been successfully used to investigate the pattern profiles in nanoimprint lithography [15][16][17].…”