High throughput defect inspection and ptychographic review for EUV mask

We have recently developed an actinic full-field EUV patterned mask inspection and review system on a tabletop by using a coherent high-harmonic generation (HHG) Extreme Ultra-violet (EUV) source. By adopting a combination of reflective-mode fly-scan scattering detecting and scanning coherent diffraction imaging methods, the actinic defects can be sensitively detected with high throughput and precisely reviewed with a finer resolution. In this work, we propose a model of a two-step EUV mask cross-scale inspection (EMCI) tactic for fast identification of actinic defects and high-resolution review of the EUV mask, which is based on difference analysis of diffracted intensities and precise ptychographic reconstruction of the EUV mask. The proposed EMCI model consists of two steps. In the first step, a fly-scan diffraction difference mapping (FDDM) method is applied to recognize and localize the defects from the EUV mask with full field of view. Thus, a sub-micron resolution defect location map is generated by array to array comparison of the diffracted intensities from the line integral of scanning regions with programmed defects, to regions of defect-free. This FDDM method works particularly in Fourier domain with no need to any form of imaging system, meanwhile, scattering information takes the advantage of high sensitivity to nanoscale defects, so that defects can be recognized and localized with high throughput and robustness. In the second step, with the location information of defects by FDDM, an EUV Ptychography (EUVP) method is applied to do the local review of EUV mask by retrieving the image of both the EUV mask and illumination based on ptychography. In this manuscript, utilizing the proposed EMCI model, we have performed a numerical simulation for EUV patterned mask defect inspection and review. The results reveal the performance of the proposed model in EUV mask metrology. The proposed method is particularly expected to have a remarkable implication for the EUV lithography.