Scanning Coherent Diffractive Imaging Method and System for Actinic Mask Inspection for Euv Lithography

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This invention presents a new method and system for inspecting extreme ultraviolet (EUV) lithography masks using scanning coherent diffractive imaging (CDI). It provides a way to quickly and sensitively detect defects on both blank and patterned EUV masks by analyzing how the mask diffracts EUV light, without the need for complex optics or prior knowledge of the illumination. The method uses ptychography algorithms to reconstruct high-resolution images and relies on deviations in diffraction patterns to highlight defects, enabling rapid and reliable quality control in semiconductor manufacturing.

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• Inspection of EUV lithography masks for semiconductor manufacturing to identify pattern and material defects.
• Quality control in mask fabrication lines for advanced semiconductor devices at technology nodes below 22nm.
• Analysis and classification of phase and amplitude defects on multilayer masks and mask blanks.
• Verification and evaluation of cleaning processes for EUV masks by detecting residual defects post-cleaning.
• Research and development in advanced mask technology and failure analysis of lithography masks.
• Adaptation of the CDI-based inspection for other high-resolution imaging in soft X-ray or BEUV applications.

BenefitsContent extracted from patent full text and abstract with AI.

• High spatial resolution imaging without the need for expensive and complex optics, reducing system cost and complexity.
• Simultaneous extraction of both amplitude and phase information, allowing detection of subtle phase defects that are otherwise hard to measure.
• No requirement for prior knowledge of the illumination or reference structures, enabling simplified and flexible inspection setups.
• Faster defect identification by analyzing deviations from expected diffraction patterns, increasing throughput in mask inspection.
• Not limited by optical depth of focus, providing easier operation and better imaging consistency.
• Applicable over large mask areas, supporting high-volume manufacturing and scalable inspection.
• Reduces the likelihood of defective masks reaching lithography processes, improving overall semiconductor yield and product reliability.

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Patent Abstract

The present invention discloses a system and a method for reflective and scanning CDI for the identification of errors in mask patterns and defects on mask blanks, comprising the steps of: a) providing a set-up for scanning the mask in reflection mode with low and/or high NA; b) illumination the mask pattern with a EUV light beam under an angle of 2 to 35°; c) detecting the diffracted light beam with a position sensitive detector; d) analyzing the detected intensities using ptychographic algorithms and thereby obtaining a high resolution image of the sample of arbitrary patterns; and e) analyzing the detected intensities for intensity variations deviating from the normal intensity distribution caused by the periodic mask pattern in order to detect defects on the mask. The present invention therefore proposes a novel technique, which can be called differential CDI. For periodically structured masks, a fast inspection can be executed by steps of multiples of period, which should give the same diffraction pattern. Subject of the present invention is that the investigation for only deviation from the normal diffraction pattern will allow rapid identification of the defects on periodic mask patterns. Compared to other CDI methods, a priori knowledge of the illumination is not needed. Both amplitude and phase are extracted whereas optics-based imaging requires through-focus imaging in order to reconstruct the phase.