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Multitask and multifunctional tools can process alternative operations, for example, LPCVD depositions of both Poly Si and SiN films with good repeatability and few particulates. Using those tools, we can reduce the total number of tools and the number of "only-one" tools which exist for a type of tool in the fab. We have also evaluated mini-fab availabilities using both a full calculation method and an approximate calculation method. The results show that tool reduction is more effective in obtaining good fab availability and uptime. The reduction of "only-one" tools is very important to improving mini-fab availability. The approximate calculation is simple for estimating the fab availability and offers the possibility to extend mega-fab estimations. It is also possible to use in the case that there are variations of MTTR, MTBF, and excess tool numbers.