Optimisation approaches for batch scheduling in semiconductor manufacturing

In this research, several approaches for the optimisation of batch processes are investigated and compared. The motivation for this is the analysis of an oven work centre in a semiconductor wafer fab. Different objectives like keeping operational due dates as well as the minimisation of lot completion time will be optimised with regard to existing process constraints. First, the problem is modelled from two different viewpoints: as scheduling problem and with the help of a simulation system. For this, it used mixed integer programming (MIP) and a discrete event simulation system respectively. As a next step, a MIP time window decomposition approach combining simulation and mathematical programming is discussed. This reduces the complexity of the given problem by solving local sub-problems. Experiments on real manufacturing data determine the optimisation potential for the work centre using the different approaches. This allows, among others, a comparison to dispatching strategies as they are used in the manufacturing line. [Received: 01 July 2009; Revised: 09 November 2009; Accepted: 01 February 2010].