Convergence towards large perimeter overlay Run-to-Run using multivariate APC system

I.IntroductionWith overlay requirements getting more and more critical, a lot of work has been done in the industry to improve the overlay correction capability by using high order process corrections, corrections per exposure and heating control (lens and reticle). Another part of the overlay budget is linked to our ability to control and stabilize it through time as well as being reactive to changes via the advanced process control system of the fab (APC)[1]. This paper describes the steps taken from an individual feedback loops configuration (one technology, one or several similar layers) to large perimeter overlay run- to-run for a high-mix 300mm semiconductor logic fab[2]. First, a multivariate APC system is defined with all the specificities needed to enable a large perimeter configuration. Then, technology/layer grouping is explained as well as filters and limits settings to start the new feedback loops simulation. The simulation phase or "learning mode" allows to have an overview on the expected gains: enhanced reactivity to parameters drift and easier maintenance by engineers in charge of following overlay run-to-run, which indirectly leads to better overall APC performance. After overlay large perimeter activation, the alert number drastically decreases, risk of measurement sampling is minimized in the fab and a similar approach is started on energy large perimeter (CD: Critical Dimensions).