Non-destructive metrology for photomasks and wafers has always been an important requirement for semiconductor lithography, and with the advent of EUVL, enabling further shrinkage of semiconductor devices, the challenges in this field have increased significantly. Coherent diffraction imaging (CDI) is a promising alternative to standard imaging for EUV photomask actinic inspection. EUV light can also be used for wafer inspection to benefit from the resolution improvement allowed by its short wavelength. In order to perform lensless imaging for patterned wafers, however, we need to probe the sample surface at grazing incidence to ensure a sufficiently high reflectance. The EUV reflective grazing incidence nanoscope (REGINE) at the Swiss Light Source was develped to perform grazing incidence lensless imaging for patterned wafers. REGINE is a tool that combines CDI, scatterometry and reflectometry in the photon energy range between 80 to 200 eV, and at the grazing incidence angle of 1 to 28 degrees. In this work, we will present the latest characterization of our system, and preliminary results.

EUV lithography is currently being used in semiconductor high volume manufacturing, however, performing non-destructive metrology at the nanoscale for different types of structures and materials is still an extremely challenging task. The EUV reflective grazing incidence nanoscope (REGINE) is a new synchrotron end-station dedicated to non-destructive EUV metrology at the nanoscale for surface/layered structures with different material compositions. REGINE is being developed at the Swiss Light Source synchrotron and aims to enable grazing-incidence coherent diffraction imaging (CDI), scatterometry, and reflectometry in the energy range of 80 to 200 eV. In this work, we present the concept of the REGINE tool and the results of its commissioning experiments.

Background: With the adoption of extreme ultraviolet (EUV) lithography in the semiconductor manufacturing, actinic EUV mask metrology has become a crucial technology to ensure the required defect sensitivity and throughput for high-volume manufacturing. Reflection-mode EUV scanning microscope (RESCAN) is a lensless actinic microscope dedicated to EUV mask metrology based on coherent diffraction imaging (CDI) as an alternative approach for EUV mask metrology and inspection.Aim and Approach: In CDI, the complex-amplitude image of the sample is obtained through its measured diffraction. Though this approach can overcome the disadvantages and limitations of conventional imaging systems, the quality of the recorded diffraction data is crucial for the reliable reconstruction of a high-resolution image. Ultimately, the signal-to-noise ratio of the recorded diffraction data depends on several parameters, such as the sample's reflectance, the quantum efficiency of the detector, its full well capacity, and the intensity of the illumination.Result: We investigate the optimal photon flux for RESCAN and provide a systematic study on the relation between the image resolution and the illumination intensity for CDI-based imaging at EUV wavelength. Conclusions:The insights provided will be helpful for the optimization of CDI for EUV imaging, in particular for increasing the throughput of EUV mask inspection with low power sources.

The reflective-mode EUV mask scanning lensless imaging microscope (RESCAN) is a synchrotron-based platform dedicated to EUV mask inspection and review at the Swiss Light Source. It is based on coherent diffraction imaging (CDI), which allows retrieving both the phase and the amplitude information of the mask surface. RESCAN has been successfully tested on masks with programmed phase and amplitude defects. A metrology method that can not only detect defects and contamination, but can also determine the material of the defects, can be a powerful tool to help identify the root cause of the defects. Here, we explore the possibility of leveraging the ability of RESCAN to detect the complex amplitude of the sample to distinguish surface defects of different materials. We fabricated a sample with random logic-like absorber patterns and pillar defects on top of a Mo/Si multilayer. We show our experimental results that show the defects of different materials exhibit specific contrast and phase values. This method can be used not only to detect the masks defects but also to identify the defect materials to a limited extent.