Resist reflow minimization via viscosity control by exposure

Abstract

Hybrid lithography is applied to the negative tone resist ma-N 405, successfully combining thermal nanoimprint lithography (to define submicron patterns) with conventional photolithography (for micrometer-pattern definition). When employing such a hybrid technology scheme, one often finds it difficult to achieve a good pattern fidelity in the overlapping areas due to uneven exposure relating to the formation of standing waves during exposure. To avoid such standing waves, one has to infer an antireflective layer. Alternatively, one can make a short heat treatment. Such a heat treatment levels the uneven exposure but may lead to a reflow of the preimprinted pattern. In order to minimize reflow during this postexposure bake, flood exposure is integrated into the processing sequence whereby the dose required must be optimized. The results show that with an adequate choice of dose for flood exposure and masked exposure, the reflow can be avoided, and the standing waves are reduced to an acceptable state. Particularly, these conditions make it possible to remove residual layers of up to 30 nm simply by development. The mixed patterns defined by hybrid lithography in this way can be successfully transferred into a metal pattern.