Actinic detection and screening of multilayer defects on EUV mask blanks using dark-field imaging

Tezuka, Yoshihiko; Ito, M.; Terasawa, Tsuneo; Tomie, Toshihisa

doi:10.1117/12.557773

Cited by 14 publications

(14 citation statements)

References 8 publications

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“…When we investigated the programmed phase defects fabricated by using ion beam deposition of Si/Mo multilayer with various sizes of CrN square dots at the bottom of the multilayer as the seeds of defects, the large bumps (dots) were shaped like truncated pyramids while the smaller ones were shaped more like Gaussians 5,10 . In this study, defects were assumed to have a Gaussian shape because the aim of this study is to investigate the detection signal of small phase defect.…”

Section: Phase Defectmentioning

confidence: 99%

“…The actinic mask blank inspection model in this study is based on an experimental tool developed at MIRAI II which consists of EUV source, illumination optics including ellipsoidal and plane mirrors, Schwarzschild optics for dark-field imaging, and an EUV-sensitive backside-illuminated CCD camera [3][4][5] . As shown in Fig.…”

Section: Dark-field Imaging For Phase Defect Detectionmentioning

confidence: 99%

“…In multilayer-coated mask blank, defects and particles on the substrate with a few nanometers in size are of serious concerns, because the topography of the defects propagates through a multilayer during the deposition, where such a multilayer structure causes a phase shift of EUV light when reflected from a mask blank. Since the phase defect is printable even though the top surface of the multilayer could be flat 9 , various inspection techniques have been investigated to detect the phase defects using EUV exposure wavelength [1][2][3][4][5][6][7][8] . In our previous work, an actinic (at wavelength) inspection with dark field imaging was experimentally demonstrated to have a capability of detecting multilayer phase defect caused by a particle defect with a height of smaller than 2 nm 5 .…”

Section: Introductionmentioning

confidence: 99%

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Multilayer bottom topography effect on actinic mask-blank inspection signal

Terasawa¹,

Tanaka²,

Suga³

et al. 2007

SPIE Proceedings

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The detectability of a small phase defect on a multilayer-coated mask blank was investigated by using electromagnetic simulation. When a smoothing deposition of multilayer coating is used the inspection signal from the phase defects is characterized not only by a top surface topography of the multilayer but also by bottom topography. To understand the impact of the bottom topography we first calculated the phase shift of reflected EUV light from multilayers with various bi-layer thicknesses since the smoothing effect may be equivalent to the local multilayer thickness variation. Then, we estimated the actinic inspection signal intensity from bump, pit, line, and groove defects taking into account the phase shift due to bi-layer thickness change and the phase change due to the top surface topography. Simulation results revealed that the phase shift due to the top surface topography was enhanced by smoothing deposition for both convex and concave shaped phase defects. Thus the bump defect is detected as higher bump than the actual height of top surface and the pit defect is detected as a deeper pit than the surface depth.

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Section: Phase Defectmentioning

confidence: 99%

Section: Dark-field Imaging For Phase Defect Detectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multilayer bottom topography effect on actinic mask-blank inspection signal

Terasawa¹,

Tanaka²,

Suga³

et al. 2007

SPIE Proceedings

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“…The system consists of EUV light source, illumination optics containing ellipsoidal and plane mirrors, Schwarzschild optics for dark field imaging, and a EUV-sensitive backside-illuminated CCD camera [3]- [5] . As described in Fig.…”

Section: Inspection Systemmentioning

confidence: 99%

“…We have been developing an actinic full-field inspection system to detect multilayer phase defects with dark field imaging [5] . Here the light scattered from the mask blank surface and then propagating in the direction between the inner and outer NAs (numerical aperture) of the inspection optics reaches a CCD camera.…”

Section: Introductionmentioning

confidence: 99%

Impact of mask blank and mirror surface roughness on actinic EUVL mask blank inspection signal

Yamane¹,

Tanaka²,

Terasawa³

et al. 2008

SPIE Proceedings

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The impact of mask blank surface roughness and mirror surface roughness on the defect inspection signal is presented. The power spectrum density (PSD) of the roughness is assumed to be inversely proportional to the square of the spatial frequency. The PSD was estimated based on the mask blank surface roughness (rms), and then the background intensity was calculated using the PSD of the spatial frequencies between the inner and outer NA. The results indicate that the larger outer NA leads to an increase in the background intensity, and that a mask blank roughness of 0.15 nm generates a background intensity of 0.15 -0.23 %. We also analyzed the effect of the mirror surface roughness on the background intensity and on the defect signal contrast. A point spread function (PSF) of scattered light from the mirror surface was calculated using the estimated PSD, and the defect images were simulated for the inspection optics by employing Fourier technique. The degradation of defect images caused by the mirror roughness was calculated by using the convolution of the PSF with the simulated images. Based on the results, it is concluded that the roughness has a large impact on the maximum intensity of the defect signal but has little effect on the background intensity. It was also learned that the degradation rate of the defect signal contrast is approximately proportional to the square of the mirror roughness.

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Mask defect inspection using an extreme ultraviolet microscope

Hamamoto

Tanaka

Lee

et al. 2005

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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A defect inspection technique on an extreme ultraviolet lithography mask is described. There are two kinds of defects, amplitude defects and phase defects due to the multilayer coating. The technique utilizes a microscope using the same 13.5 nm wavelength as the light used for exposure, and producing a magnified image of defects on a mask. Using this microscope, amplitude defects on practical masks and phase defects are observed. A phase defect was formed by a multilayer coated on a line pattern with a height of 5 nm and width of 90 nm on a glass substrate. Although the detected defect is made beforehand, it is detected by reflection of the light which penetrated inside of a multilayer. These results show that it is possible to detect the internal reflectivity distribution, without depending on surface perturbations.

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Actinic detection and screening of multilayer defects on EUV mask blanks using dark-field imaging

Cited by 14 publications

References 8 publications

Multilayer bottom topography effect on actinic mask-blank inspection signal

Multilayer bottom topography effect on actinic mask-blank inspection signal

Impact of mask blank and mirror surface roughness on actinic EUVL mask blank inspection signal

Mask defect inspection using an extreme ultraviolet microscope

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