Monitoring changes in photomask defectivity

A reticle that is within specifications is inspected so as to generate a baseline event indicating a location and a size value for each unusual reticle feature. After using the reticle in photolithography, the reticle is inspected so as to generate a current event indicating a location and a size value for each unusual reticle feature. An inspection report of candidate defects and their images isgenerated so that these candidate defects include a first subset of the current events and their corresponding candidate defect images and exclude a second subset of the current events and their corresponding excluded images. Each of the first included events has a location and size value that fails to match any baseline event's location and size value, and each of the excluded second events has alocation and size value that matches a baseline event's location and size value. 本发明揭示检验在规格内的光罩以便产生指示每异常光罩特征的位置和尺寸值的基线事件。于在光刻中使用所述光罩后，检验所述光罩以便产生指示每异常光罩特征的位置和尺寸值的当前事件。产生候选缺陷和其图像的检验报告，使得这些候选缺陷包含所述当前事件的第子集和其对应的候选缺陷图像，且排除所述当前事件的第