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As the industry marches on onto the 5nm node and beyond, scaling has slowed down, with all major IDMs & foundries predicting a 3-4 year cadence for scaling. A major reason for this slowdown is not the technical challenge of making features smaller, but effective control of variation that creeps in to the fabrication process. That variability manifests itself as edge placement error (EPE), which has a direct impact on wafer yield. Simply defined as the variance between design intent vs. actual on-wafer results, EPE is one of the foremost challenges being faced by the industry at the advanced node for both logic and memory. This is especially critical at three stages: the front end of line (FEOL) STI patterning; middle of line (MOL) contact patterning; and back end of line (BEOL) trench patterning where the desired tight pitch demands EPE control beyond the capability of 193i multi-patterning or even EUV single pattern. In order to mitigate this EPE challenge, we are proposing self-alignment of blocks & cuts through a multi-color materials integration concept. This approach, termed as “Self-aligned block or Cut (SAB or SACut)”, simply trades off the un-manageable overlay requirement into a more manageable etch selectivity challenge, by having multiple materials filled in every other trench or line.
In this paper we will introduce self-alignment based block and cut strategies using multi-color materials integration and show implementation for BEOL trench block patterning. We will present a breakdown of the key unit process challenges that were needed to be resolved for enabling the self-alignment such as: (a) material selection of multi-color approach; (b) planarization of spin on materials; (c) void-free gap fill for high aspect ratio features; and last but not the least, (c) etch selectivity of etching one material with respect to all other materials exposed. Further, we will present a comparison of our new self-alignment approach with standard approaches where we will articulate the advantages in terms of EPE relaxation and mask number reduction. We will conclude our talk with a brief snapshot of the future direction of our EPE improvement strategies and our view on the future of patterning beyond 5nm node for the industry.
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