Overlay models for nanoimprint lithography

Abstract

Nanoimprint lithography (NIL) manufacturing equipment utilizes a patterning technology that involves the field-by-field deposition and exposures of a low-viscosity resist deposited by jetting technology onto the substrate. The technology faithfully reproduces patterns with a higher resolution and greater uniformity compared to those produced by photolithography equipment. Previous studies have demonstrated NIL resolution better than 10 nm, making the technology resolution suitable for the patterning of several generations of critical memory levels with a single mask. Overlay is critical for advanced memory devices such as dynamic random-access memory and phase change memory. Both device types continue to scale, with expected half pitches down to 14 nm and beyond. Typical overlay budgets are on the order of 20% of the half pitch, meaning overlay requirements of <3 nm. Previously, we have employed systems (such as high-order distortion correction) to improve upon higher order distortion errors, thereby improving the overlay performance of our process. Some process variables that are unique to NIL and that can be considered as process tunable variables include imprint force and tip/tilt of the imprint head relative to the wafer. These were identified to be significant variables to further improve the overlay and to achieve good overlay stability in a production run at throughput. We introduce these overlay tuning knobs for NIL and present the techniques and models to achieve stability of imprint force and tip/tilt in order to reduce both wafer to wafer variation as well as the field–field variation of these variables. Applying these techniques enables NIL to meet the overlay requirements for advanced memory device production.