CD measurement for next-generation mask

Since higher Critical Dimension (CD) accuracy on mask is required, there is a need to optimize CD definition for lithography. The conventional CD definition is based on the cross-sectional profile of mask pattern, but the cross-sectional profile does not reflect aerial image on wafer. Therefore, CD definition based on aerial image on wafer is preferable to the cross-sectional profile. We formulated a CD definition that reflects aerial image on wafer. In our definition, CD is called CDad. There are two types of CD measurement equipment: top view type such as CD-SEM, and transmitted light type such as deep-UV microscope. By simulation and experiment, we evaluated CD of top view and CD of deep-UV microscope to obtain CDad. The results show that CDad can be obtained with deep-UV microscope, but not to top view. Deep-UV microscope is available for CD measurement of 0.11 and 0.13 um generation masks.