Two-Step curing method for demoulding in UV nanoimprint lithography

In the UV nanoimprint lithography (UV NIL), it is obvious that the resist curing process is dependent on the UV dose, therefore three states of the resist pattern, i.e., uncuring, undercuring and full-curing may occur due to an inadequate curing control method. Also the demoulding force, which can influence the pattern transferring fidelity, is largely determined by the resist-curing degree. For acquiring high pattern transferring fidelity with small demoulding force, a new demoulding method is proposed in this paper. Through an analysis of the three different pattern transferring results, i.e. rounded-feature replication, fine replication, and scooped-feature replication, which may be induced by the different resist-curing degree and the relative demoulding force, it is found that the resist-curing degree is a critical factor which affects the pattern transferring fidelity. In addition, when the resist-curing degree is too low or too high, either the imprint mould may be stained or the microstructures on the mould can be damaged, which will adversely affect the subsequent imprints in a step-and-repeat process. A new demoulding method is presented, which consists of two UV exposures. The first UV exposure is done before demoulding to under-cure the resist pattern so that the demoulding force can be reduced while maintain a short-time pattern stability. The second UV exposure follows the demoulding to full-cure the resist so as to produce a sufficient rigidity in the pattern. It is experimentally shown that this new demoulding method leads to high pattern fidelity and a small demoulding force while minimizing the mould containments or microstructures damage on it.