Defect is a killing factor in photomask fabrications. For 65nm node photomask fabrication, even smaller than 1 um particle can cause hard-to-repair defect. And it is not easy to find the defect source and solve it. For this reason, the process monitoring system that shows us current defect trend rapidly and effectively is highly required. At the same time, this system can be used for verifying the process stability and detecting unusual signals in process.