Feedback control for priority rules in re-entrant semiconductor manufacturing

Typical semiconductor production is re-entrant and hence requires priority decisions when parts compete for production capacity at the same machine. A standard way to run such a factory is to start to plan and to finish according to demand. Often this results in a push policy where early production steps have priority over later production steps at the beginning of the production line and a pull policy where later steps have priority at the end of the production line. The point where the policies switch is called the push-pull-point (PPP). We develop a control scheme based on moving the PPP in a continuum model of the production flow. We show that this control scheme significantly reduces the mismatch between demand and production output. The success of the control scheme as a function of the frequency of control action is analyzed and optimal times between control actions are determined.