Accuracy of wafer level alignment with substrate conformal imprint lithography

Substrate conformal imprint lithography (SCIL) is an innovative soft lithography method for the transfer of large area nanostructures. This technology was originally invented by Philips Research. With the implementation of the SCIL process on mask aligners, the standard alignment options of a mask aligner were also available for SCIL. This work presents studies on overlay alignment accuracy of the SCIL process on mask aligners. The utilized alignment markers were common box-in-box fiducials. With these structures, the alignment accuracy was determined. The experiments showed that the SCIL process induces a shift of the stamp with respect to the stage in imprint direction during the initial movement of the stamp from the SCIL actuator to the substrate. This shift is reproducible and depends on the distance between the actuator and the substrate. With an offset correction of the stage, this shift could be compensated. The achieved alignment accuracy was then below one micrometer, limited just by the mechanical capabilities of the mask aligner. Besides, global and local distortions of the imprinted structures with respect to the original master structures were identified and analyzed within this work. It was found that there is no systematic distortion of structures in the stamp due to the imprint process itself despite using the flexible composite SCIL stamps with polydimethylsiloxane pattern layer. Only nonsystematic local distortions could be found. Finally, the accuracy of the stamp manufacturing process for the SCIL stamps was investigated, and it was found that large distances in the centimeter range between single features are reproduced with a variation of 0.06‰. All together, the results of this work show that an accurate and reproducible overlay alignment of imprinted lithography layers is possible using SCIL as a wafer scale imprint technology.