Zernike phase contrast microscope for EUV mask inspection

Wang, Yow-Gwo; Miyakawa, Ryan; Neureuther, Andrew R.; Naulleau, Patrick

doi:10.1117/12.2048180

Cited by 6 publications

(9 citation statements)

References 5 publications

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“…We recognize that this technique has the potential to enhance the contrast of phase defects and phase features on EUV masks in a similar way, thus improving the sensitivity of actinic mask imaging or inspection tools. 9 Zernike phase contrast microscopy in the soft x-ray spectral range using a zoneplate lens and phase ring has been demonstrated by Schmahl et al 10 With well-collimated illumination, the required phase shift of the undiffracted light can be achieved within the zoneplate pupil, sparing the need for an additional phase-shifting element, and simplifying the design and alignment. 11 Figures 4(a) and 4(b) show cartoons of a standard, off-axis zoneplate and an off-axis zoneplate for Zernike phase contrast, in comparison.…”

Section: Zernike Phase Contrastmentioning

confidence: 99%

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Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

Benk

Miyakawa

Chao

et al. 2015

J. Micro/Nanolith. MEMS MOEMS

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Abstract. The authors are expanding the capabilities of the SHARP microscope by implementing complementary imaging modes. SHARP (the SEMATECH High-NA Actinic Reticle Review Project) is an actinic, synchrotron-based microscope dedicated to extreme ultraviolet photomask research. SHARP's programmable Fourier synthesis illuminator and its use of Fresnel zoneplate lenses as imaging optics provide a versatile framework, facilitating the implementation of diverse modes beyond conventional imaging. In addition to SHARP's set of standard zoneplates, we have created more than 100 zoneplates for complementary imaging modes, all designed to extract additional information from photomasks, to improve navigation, and to enhance defect detection. More than 50 new zoneplates are installed in the tool; the remaining lenses are currently in production. We discuss the design and fabrication of zoneplates for complementary imaging modes and present image data, obtained using Zernike phase contrast and different implementations of differential interference contrast (DIC). First results show that Zernike phase contrast can significantly increase the signal from phase defects in SHARP image data, thus improving the sensitivity of the microscope. DIC is effective on a variety of features, including phase defects and intensity speckle from substrate and multilayer roughness. The additional imaging modes are now available to users of the SHARP microscope.

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Section: Zernike Phase Contrastmentioning

confidence: 99%

“…Furthermore, it may be useful to apply apodization to balance the amplitudes and to optimize the contrast of the interfering elements of the field. 9 Improvements in contrast will be studied for common types of phase, amplitude and combined phase and amplitude defects, and found on blank and patterned regions of EUV photomasks.…”

Section: Zernike Phase Contrastmentioning

confidence: 99%

Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

Benk

Miyakawa

Chao

et al. 2015

J. Micro/Nanolith. MEMS MOEMS

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“…A narrower defect has larger scattering angle and thus not all the photons can be collected by the pupil. Wider defects have smaller scattering angle but more and more of the scattered light passes through the central phase shifted region thus the effect of phase contrast for this portion of the light will be negated [1]. The absorption component of the defect improves the in-focus component for large defects to the point that a nearly similar and adequate SNR is obtained in focus for larger defects.…”

Section: Change In Nature Of Programmed Defects With Size and Inspectmentioning

confidence: 96%

“…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%

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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“…The constant phase shift among every zone can reduce the potential to introduce unexpected aberration into the Fresnel zoneplate. Moreover, this variable allows the user to 11 determine the trade-off between file size (number of trapezoids) and the error tolerance on their zoneplate pattern design. Figure 10 shows the impact of selected precision on file size for three different zoneplate sizes (number of zones).…”

Section: Trapezoid Representation Of the Zoneplate Patternmentioning

confidence: 99%

Efficient Fresnel zoneplate pattern data preparation for high-resolution nanofabrication

Wang

Miyakawa

Chao

et al. 2017

Optics Communications

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Abstract.A Fresnel zoneplate is a diffractive optical element consisting of concentric rings (zones) for which the transmitted light produces a focal spot that is used in all wavelength regimes, including x-rays. The pattern of transmission openings determines the location of the spot and the sub-half wavelength size of the openings can adjust the intensity. Today, very general transmission zoneplate patterns are used for many special imaging and image compensation purposes. Manufacturing zoneplates require a zoneplate pattern file, which precisely describes the size, shape, and contour of the rings based on the desired optical properties of the lens. Generating such a pattern requires the delicate balance of achieving the required optical performance while maintaining manageable file sizes and computation times. Here we describe a new algorithm meeting these needs. By precisely controlling the number of shapes in each zone, the algorithm simultaneously optimizes the desired optical tolerances with the pattern file size.

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Zernike phase contrast microscope for EUV mask inspection

Cited by 6 publications

References 5 publications

Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

Broader view on extreme ultraviolet masks: adding complementary imaging modes to the SHARP microscope

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

Efficient Fresnel zoneplate pattern data preparation for high-resolution nanofabrication

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