Effect of residual stress on replication fidelity with nanoimprint

Abstract

Relief of residual stress in an imprinted polymer may affect the replication fidelity by leading to recovery. The level of stress induced in the polymer depends on the method of imprint. For example, a “soft” imprint with an elastomeric stamp uses capillary forces to fill the cavities whereas a “hard” imprint with a rigid stamp relies on external pressure. To study the effect of residual stress after imprint, both methods are applied with different imprint times to vary the level of residual stress, as the stress remaining relaxes with imprint time. To visualize the residual stress a temperature treatment is performed after imprint. This temperature treatment allows recovery within a convenient experimental time. A comparison of the shape of the imprinted structures before and after temperature treatment clearly shows that with a hard imprint at short imprint times a considerable amount of stress remains in the polymer, in particular when the residual layer is thin and the imprinted stamp structures are wide. With a soft imprint residual stress is not evident. Similar results are obtained with a thermoplastic material and a crosslinking material (SU-8); however, with the latter recovery remains limited due to a decrease of mobility during crosslinking. Residual stress is of major importance for the replication fidelity with short imprint processes.

Influence of thermal diffusion and shear thinning during the leveling of nanoimprinted patterns in a polystyrene thin film

“…• C for 2 hours to erase any residual stresses due to the polymer flow as pointed out by Ro et al [27] and Papenheim et al [28]. The wafer is then sliced into samples of 2×2 cm and only 4 samples are retained to ensure a polymer thickness variation lower than 1 nm between one another.…”

Complex 3D structures via hybrid processing of SU-8

“…Before cross-linking, SU-8 is thermoplastic and suitable for thermal nanoimprint (T-NIL) at temperatures as low as 90°C due to the low glass transition temperature [25]. Furthermore, it has an excellent capability with capillary force lithography (CFL) [26,27].…”

Mechanism of forming defects in roll-to-roll hot embossing of micro-pyramid arrays: II. Numerical study

“…Scheer et al [36] concluded that the processing time chosen for thermal nanoimprint should be longer than the flow time constants of the polymer material to allow elimination of elastic recovery through complete disentangling of molecular chains. By annealing the structures replicated by thermal nanoimprint lithography, Ro et al [37] and Papenheim et al [38] demonstrated that processing-induced residual stress in the polymer may affect replication fidelity significantly by leading to recovery. Shan et al [39] studied the deformation and recovery of PMMA material below T g using a nano-indentation technique and both instantaneous and retarded recovery were observed.…”