From spreadsheets to simulations: a comparison of analysis methods for IC manufacturing performance

Illustrates the differences between spreadsheet and simulation models through the examples of diffusion cell staffing, material flows through a process segment, and the operations of a full fab. The results show that engineering judgment applied to spreadsheet outputs is not the most prudent solution when more realistic tools are available, and, that by overstating capacity, spreadsheet logic can lead to a lack of key equipment and space. Using similar input data, simulation models provide capacity estimates, as well as WIP (work in process) and cycle time predictions, which take into account the interactions between lots, machines, and people. Generally speaking, the spreadsheet model is inadequate for modeling the coordinated use of several types of resources. Until recently, the spreadsheet was still preferred in spite of its limitations because of the vast amounts of computing resources required for simulation runs. It is concluded that the advent of cheap and powerful workstations has made this a moot point