<title>Layer-to-layer alignment for step and flash imprint lithography</title>

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The Step and Flash Imprint Lithography (SFIL) process is a low-cost, high-throughput patterning technique with a sub- 100 nm resolution capability. Investigation by this group and others indicates that the resolution of replication by imprint lithography is limited only by the size of the structures that can be created on the template. It has also been demonstrated that the SFIL process is capable of eliminating contaminants from the template (master) during a step and repeat imprinting process. The low pressure, room temperature nature of SFIL and the transparent imprint templates make it particularly attractive for high- resolution layer-to-layer alignment. Another aspect of SFIL that assists in the layer to layer alignment is the presence of a thin layer of low viscosity liquid between the template and wafer prior to UV curing. The liquid maintains a small gap (~0.2 micrometers ) and acts as lubrication and damping agents, which allows for accurate in situ error measurement and compensation. In this paper, we present results from overlay alignment experiments using the SFIL process. A Canon mask aligner was modified to implement a layer-to-layer alignment scheme for SFIL. The objective of this research was to achieve alignment accuracy of about 0.5 micrometers , which is the practical limit of the X-Y stage in the mask aligner. The overlay alignment error measurements and the corresponding corrections in X,Y and Theta were performed using the modified mask aligner. In its current state, the alignment resolution appears to be limited by the resolution of the mask aligner stage. It is expected that other high resolution alignment techniques have been developed for optical projection lithography and X-ray lithography processes can be adapted to the SFIL process to significantly improve the alignment resolution.