Advanced process control applied to metal layer overlay process

Abstract

Overlay control of printed layers onto processed metal levels highly depends on the process influences to the alignment and overlay measurement targets. This study characterizes the systematic influence to both alignment and overlay metrology based on AlCu deposition and W CMP. The systematic influence of AlCu deposition to alignment and overlay targets are explored in theory and then verified experimentally. Both theory and experimental results are then validated empirically as “non-zero” overlay control is applied to high volume production to increase wafer edge yield. The influence of W CMP on lot-to-lot overlay performance is also characterized and accounted for to further improve metal one overlay performance. The emphasis of this paper will be model-based Advanced Process Control (APC). Methods used to characterize process influence on overlay for a back-end metal process will be discussed. We will then describe how predictive overlay was modeled in terms of AlCu deposition target life, W CMP endpoint as well as normal control context such as exposure tool and part id. The challenge of implementing APC for increased context partitioning is discussed and the need for a model-based approach is stressed. The methodology used for lot disposition in the case of “non-zero” targeted overlay is also explained.