Research and optimization of electronic charge phenomena on CDSEM imaging of binary photomask

Abstract

CD-SEM is widely used to determine photomask CD performance, SEM image accuracy is crucial for CD measurement. SEM image blurring caused by charging on a type of binary photomask is a major issue we encounter during manufacturing, not only the image form is not clear on Isolated Clear patterns, also obvious CD deviation is observed on Isolated Dark patterns. We investigate into this issue and search for methods to remove residual charge on photomask. We found that these residual charge cannot be removed by electrolyte solutions in cleaning process but will disappear after a few days in fabrication environment. Furthermore, we found these phenomena reappear after UV radiation in close distance or O2 plasma sputtering on the photomask. In this research, we prove that sputtering a mixture gases plasma can effectively eliminate this phenomenon without any negative impact on the binary photomask itself.