EUV scatterometry-based measurement method for the determination of phase roughness

AFM-based roughness measurement reveals the topography of EUV masks, but is only sensitive to the top surface [1]. Scatterometry provides a more accurate approach to characterize the effective phase roughness of the multilayer, and it becomes important to determine the valid metrology for roughness characterization. In this work, the power spectral density calculated from scatterometry is compared to that from AFM for measurements before and after coating of substrates with a range of roughness levels. Results show noticeable discrepancies between AFM- and scatterometrymeasured roughness, and indicates that when the physical surface roughness increases with deposition the EUV penetration into the multilayer tends to mitigate this effect. In this paper, we describe an EUV scatterometry-based measurement method for the determination of phase roughness with the goal of minimizing the amount of physical scattering data to be collected and rendering the method compatible with potential future standalone EUV reflectometer tools.