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.