EUV mask defect material characterization through actinic lensless imaging

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.

Automated summary

The RESCAN platform, based on coherent diffraction imaging (CDI), has been used for EUV mask inspection and review. It has shown the ability to detect both phase and amplitude defects on masks. This study explores the possibility of using RESCAN to distinguish surface defects of different materials and proposes a feasible method.