An Impedance-Based Force Control Scheme to a Plate-to-Plate Nanoimprinter

Nanoimprint lithography (NIL) is a novel technique that utilizes direct deformation of the resist to fabricate micro/nanometer scale patterns. NIL outperforms traditional photolithography technology for its low cost, high productivity, and high repeatability. For a general plate-to-plate NIL, it is of central importance to precisely control the embossing force during the entire embossing process to tune the orientation of the imprint head and also to guarantee the uniformity and fidelity. Existing approaches used in NIL are position-based feedback controls. However, a position signal is believed to be indirect and is more likely to be influenced by the thickness of the photoresist layer. To address this problem, in this paper, we propose a two-stage force control scheme to explicitly control the embossing force based on the impedance control framework. The first stage is to parallelize the template surface with the substrate surface using the small initial contact force before embossing. Then, the second control stage is to regulate the large embossing force to the desired value. With the proposed force control approach, the embossing force can be explicitly controlled during the entire stamp process even without a prior knowledge of the environmental parameters. Experimental tests performed on a 500-nm grating scale further illustrate and verify the effectiveness of the proposed design.