Strategy for a loading force induced overlay position shift in step imprint lithography

Imprint lithography has the potential to be a cost-effective successor to optical lithography, but there are a number of problems that need to be solved for this to happen. Imprint lithography is a mechanical process, and the overlay for imprint lithography depends not only on the alignment measurement accuracy but also on the loading force used for pattern transferring. A large force seriously deteriorates the overlay accuracy. How to eliminate the influence of loading force on the overlay accuracy is a practical challenge. This paper proposes a step imprint lithography tool for multilayer microstructure fabrication and emphasizes the importance of reporting the overlay process development. The loading process is investigated first. Relative movement and interaction force between the mould and the wafer are two main causes for an overlay position shift in the loading process. Though it can be compensated by the readjustment process, the deformation recoveries of the mechanical system in the demoulding process still bring about serious deterioration in pattern fidelity and overlay accuracy. An optimized overlay process is proposed to solve these problems. Some crucial issues in the optimized overlay process, like loading force optimization, the load pre-release process, and the demoulding process, are investigated by experiments to determine the best performing approaches using the developed step imprint lithography (SIL) tool. It was found that the proposed overlay process can eliminate the influence of loading force effectively.