Phase-enhanced defect sensitivity for EUV mask inspection

Wang, Yow-Gwo; Miyakawa, Ryan; Chao, Weilun; Goldberg, Kenneth A.; Neureuther, A. R.; Naulleau, Patrick

doi:10.1117/12.2069291

Cited by 6 publications

(9 citation statements)

References 1 publication

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“…Zoneplates with central phase shift of 45° and 90° and various level attenuation down to 0.08 intensity transmission were constructed. The experiment results presented here confirm previously presented simulation results [1,2] of the advantages of Zernike phase contrast inspection. Examples of the effects of blended defects with both phase and absorption show that the absorption causes the problematic null in pure phase defect to shift off-axis.…”

Section: Resultssupporting

confidence: 93%

“…Verifying our previous simulation results [2] that we can use phase shifts other than 90º in order to observe phase and absorber defects with a single scan at focus thereby improving the inspection throughput. More importantly, we can achieve a SNR up to 8 for a phase defect with a height of only 0.35 nm.…”

Section: Enhanced Defect Sensitivity Using Phase Contrast Methods Withsupporting

confidence: 66%

“…In order to further improve the SNR, we apply apodization in the pupil to suppress the low frequency components of the speckle noise from surface roughness while at the same time increasing the contrast of the defect by lowering the DC interferometric reference wave component [2]. For this test we consider a native defect found on the mask with an effective size of 1.23 nm × 120 nm.…”

Section: The Relationship Between Signal and Noise Under Apodizationmentioning

confidence: 99%

“…To address this issue, the use of the Zernike phase contrast microscope for EUV actinic blank inspection has been proposed [1,2]. Zernike phase contrast is capable of detecting phase defects at best focus by enhancing the signal to noise ratio (SNR) through directly interference between the scattered and unscattered light, and the apodization in the pupil plane can further suppress the speckle noise to improve the SNR of the phase defect.…”

Section: Introductionmentioning

confidence: 99%

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Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection

et al. 2015

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In this paper, we present an experimental verification of Zernike phase contrast enhanced EUV multilayer (ML) blank defect detection using the SHARP EUV microscope. A programmed defect as small as 0.35 nm in height is detected at focus with signal to noise ratio (SNR) up to 8. Also, a direct comparison of the through-focus image behavior between bright field and Zernike phase contrast for ML defects ranging from 40 nm to 75 nm in width on the substrate is presented. Results show the advantages of using the Zernike phase contrast method even for defects with both phase and absorption components including a native defect. The impact of pupil apodization combined with Zernike phase contrast is also demonstrated, showing improved SNR is due to the stronger reduction of roughness dependent noise than defect signal, confirming our previous simulation results. Finally we directly compare Zernike phase contrast, dark field and bright field microscopes.

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Section: Resultssupporting

confidence: 93%

Section: Enhanced Defect Sensitivity Using Phase Contrast Methods Withsupporting

confidence: 66%

Section: The Relationship Between Signal and Noise Under Apodizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection

et al. 2015

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“…For example, a zone plate can be used to create a phase contrast objective lens that, unlike a conventional lens, causes phase objects to produce strong contrast near focus [33][34][35]. To demonstrate the algorithm's ability to consider an arbitrary pupil function and partial coherence, measurements were taken using two lenses: a standard zone plate that results in conventional imaging and an unapodized phase contrast zone plate with a circular, 90 • phase shifting region of radius 0.3× the imaging NA.…”

Section: Methodsmentioning

confidence: 99%

Quantitative phase retrieval with arbitrary pupil and illumination

et al. 2015

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We present a general algorithm for combining measurements taken under various illumination and imaging conditions to quantitatively extract the amplitude and phase of an object wave. The algorithm uses the weak object transfer function, which incorporates arbitrary pupil functions and partially coherent illumination. The approach is extended beyond the weak object regime using an iterative algorithm. We demonstrate the method on measurements of Extreme Ultraviolet Lithography (EUV) multilayer mask defects taken in an EUV zone plate microscope with both a standard zone plate lens and a zone plate implementing Zernike phase contrast. Am. 73, 1434Am. 73, (1983. 5. J. R. Fienup, "Phase retrieval algorithms: a comparison," Appl. Opt. 21, 2758Opt. 21, -2769Opt. 21, (1982. 217, 408-432 (1953). 32. C. Chang, A. Sakdinawat, P. Fischer, E. Anderson, and D. Attwood, "Single-element objective lens for soft x-ray differential interference contrast microscopy," Opt. Lett. 31, 1564Lett. 31, -1566Lett. 31, (2006. 33. F. Zernike, "Phase contrast, a new method for the microscopic observation of transparent objects," Physica 9, 686-698 (1942

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Source performance metrics for EUV mask inspection

Juschkin¹,

Wack²

2022

J. Micro/Nanopattern. Mats. Metro.

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Rules are derived to obtain specifications on radiance, power, lifetime, and cleanliness of the source for an actinic patterned mask inspection system. We focus on the physical processes and technological aspects governing the requirements of radiation sources for reticle inspection. We discuss differences and similarities to scanner with respect to magnification, system etendue, and image recording. Source radiance requirements are estimated from a perspective of targeted throughput and defect detection sensitivity. The derivations consider the influence of photon shot noise on signal detection and conservation laws of light etendue and radiant flux. We describe the scaling laws for required radiance with targeted sensitivity index, optical contrast, field size, and system throughput. In addition, we address the limits on the required brightness and minimum repetition rate set by mask damage threshold. Finally, system and source cleanliness requirements and criticality of the source availability and lifetime are discussed. The analysis can be applied to other microscopy-based metrology and inspection applications.

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Phase-enhanced defect sensitivity for EUV mask inspection

Cited by 6 publications

References 1 publication

Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection

Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection

Quantitative phase retrieval with arbitrary pupil and illumination

Source performance metrics for EUV mask inspection

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