The demands on CD metrology techniques in terms of both reproducibility and measurement uncertainty increase with decreasing critical dimensions (CD) on lithography masks. Additionally a full 3D characterization of the mask structures becomes more and more important to understand and control the printing behavior of state of the art photomasks. Furthermore, an extension of metrology characterization including material properties can provide the final puzzle pieces for a better correlation of mask metrology to wafer metrology. Here, optical metrology systems, especially at-wavelength systems, are very well suited to characterize structure features of a photomask regarding their printing behavior on a wafer. In particular scatterometry is able to provide a better understanding of the investigated structure and allows for modeling of secondary structure parameters as well as material composition. AMTC has a commercial scatterometer from n&k Technology (n&k 5700-CDRT) in use. This system measures the spectral transmission and reflection, the 0th diffraction order. Beside thin film characterization this system is used for CD and edge profile characterization, also. The analysis of the data uses a look-up table approach in combination with a database, which has been generated and can be expanded, respectively, using a RCWA based software. At PTB we have realized a new DUV hybrid scatterometer which combines essential elements of a radiometer, an ellipsometer, and a diffractometer. These two systems are different both in terms of the measurement modes, the data evaluation method and the Maxwell-solver used. Therefore we started to compare the performance of both systems to traditional metrology system for CD metrology and phase measurement. For this purpose we performed first comparative scatterometric measurements on a MoSi phase shifting mask.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.