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Preventive maintenance is a valuable tool in minimizing unexpected tool downtime in semiconductor fabs. This thesis is spawned from the research project, "Preventive Maintenance1 in Semiconductor Fabs", sponsored by the Semiconductor Research Corporation (SRC) and International SEMATECH. The project is a joint venture between the University of Cincinnati and University of Maryland that looks to improve the planning and scheduling of preventive maintenance (PM) on tools in semiconductor fabs. The project proposes a two-level hierarchical optimization structure that considers important factors such as the work-in-progress (WIP) at a tool and the complex relationships between the chambers of a cluster tool. This thesis focuses on the lower level of the aforementioned hierarchy that deals with PM scheduling. It expands on the work accomplished thus far in the project, specifically analyzing and fixing current issues with the PM scheduling algorithm and creating a software implementation of the scheduling algorithm.