KEYWORDS: Signal to noise ratio, Diffraction, Background noise, Interference (communication), Denoising, Analog to digital converters, Analog electronics, Photons, Electrons, Education and training
Diffractive imaging techniques, such as coherent diffraction imaging (CDI), ptychography, and Fourier ptychography, have gained popularity due to their ability to recover the amplitude and phase information of samples simultaneously from the diffracted pattern with super resolution and wide field of view. However, imaging noise can significantly degrade the reconstructions in diffractive imaging. Higher order diffractions, in particular, are sensitive to measurement noise due to their lower signal-to-noise ratios (SNR) compared to lower orders. Existing denoising methods cannot effectively separate signals from detector noise. To address this limitation, we propose a self-adaptive noise minimization approach using a regularized regression method. Our approach involves training a regularized linear regression model to evaluate the power of noise level in the recorded noisy diffraction patterns and the detector's dark noise. This results in a refined pattern with high SNR. We evaluate our approach on synthetic and experimental datasets and compare it with existing noise reduction methods. The results demonstrate that our method significantly outperforms other state-of-the-art methods in terms of both noise reduction and preservation of fine structural details. Moreover, our approach does not require any prior knowledge or assumptions about the noise statistics, making it a robust and versatile method for diffractive imaging applications.
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.
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