Rigorous simulation of defective EUV multilayer masks

Sambale, Christoph; Schmoeller, Thomas; Erdmann, Andreas; Evanschitzky, Peter; Kalus, Christian K.

doi:10.1117/12.518049

Cited by 5 publications

(3 citation statements)

References 6 publications

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“…1(a) can still be critical printable defects as are predicted by EM simulation. 4 On top of that, small bumps with the same volume and hence with the same visible signal can have different printability due to different origins of defects as schematically shown in Fig.1 (b). This confusion could generate many nuisance defects that need to be followed by thorough characterization possibly using EUV microscope to identify the potential defectivity of each defect, which can induce enormous workload.…”

Section: Introductionmentioning

confidence: 97%

Actinic detection of multilayer defects on EUV mask blanks using LPP light source and dark-field imaging

et al. 2004

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The development of defect-free mask blanks including inspection is one of the big challenges for the implementation of extreme ultraviolet lithography (EUVL), especially when the introduction of EUVL is rescheduled to a later technology node. Among others, inspection of multilayer coated mask blanks with no oversight of critical defects and with minimal detection of false defects is a challenging issue for providing mask blanks free of defects or with thorough characterization of any existing defects. MIRAI Project has been developing a novel actinic (at-wavelength) inspection tool for detecting critical multilayer defects using a dark-field imaging and a laser-produced plasma (LPP) light source, expecting better sensitivity and better correlation with printability. The first experimental set up is completed for proof-of-concept (POC) demonstration using 20x Schwarzschild imaging optics and a backsideilluminated CCD.An in-house LPP light source is integrated to optimally illuminate the area of interest by EUV with a wavelength of 13.5nm. For its illuminator, a multilayer-coated elliptical mirror is used to illuminate a mask blank with the EUV that is collected within a wide solid angle from the light source. The first EUV dark-field image is obtained from a mask blank with programmed multilayer defects which are manufactured by locating well-defined patterns before depositing Mo/Si multilayer on EUV mask substrate. All the fabricated multilayer defects down to 70nm in width and 3.5nm in height are detected as clear signals that are distinguishable from the background intensity arising from the scattering by the surface roughness of the multilayer-coated mask blank. We have also detected a phase defect as low as 2nm in height. False defect count was not only zero within the area of view but also statistically confirmed to be less than one within the whole area of a mask blank assuming the extrapolation of observed fluctuation of background intensity is applicable. EUV pulse energy measurements and a CCD speed scaling suggested that the inspection throughput of 2 hours per mask blank will be feasible. The actinic tool based on this scheme will, not only serve for benchmarking with non-actinic tools or support multilayer deposition process improvements, but also be a viable choice for qualification of premium EUV mask blanks.

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Section: Introductionmentioning

confidence: 97%

Actinic detection of multilayer defects on EUV mask blanks using LPP light source and dark-field imaging

et al. 2004

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“…In other words, visible/UV inspection is only sensitive to the top surface of the multilayer while the defect printability also depends on the smoothing of the multilayer or the morphology of the multilayer underneath. For example, line defects that are completely smoothed out during multilayer deposition can still be critical printable defects as are predicted by EM simulation 6 . It should be quite reasonable from an economic perspective to pursue visible/UV solution for detecting critical defects on multilayer-coated mask blanks, not only by improving inspection sensitivity of the tool but also by devising multilayer deposition process to avoid emergence of undetectable defects such as by introducing non-smoothing multilayer deposition process for the upper part of multilayer.…”

Section: Introductionmentioning

confidence: 98%

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

et al. 2004

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MIRAI Project has developed a novel actinic (at-wavelength) inspection tool for detecting critical multilayer defects on EUV mask blanks using a dark-field imaging and a laser-produced plasma (LPP) light source. The first milestone of proof-of-concept was successfully achieved by demonstration of programmed defect detection accurate to 70nm in width and 2nm in height without any detection of false defects 1 . Characterization of this experimental actinic inspection tool is ongoing to define the detailed specification of a proto-type tool. One of the important factors that define the sensitivity of the inspection tool is the signal to noise ratio available from the inspection image. In this paper, characterization results of background fluctuation and through focus imaging are presented.The characterization of background fluctuation suggested that the pixel-to-pixel fluctuation by spatial fluctuation of roughness is smaller than originally assumed possibly because of the smoothing by the aberration of the imaging optics. The negative impact of the degradation of defect signal by the aberration at the best focus is relaxed due to the smoothed fluctuation of the background intensity.

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“…For example, line defects that are completely smoothed out during multilayer deposition can still be critical printable defects as predicted by electromagnetic (EM) simulation. 5) It should be quite reasonable from an economic perspective to pursue the extension of visible/UV solution for qualifying defect-free mask blanks. These activities include not only improvement in inspection sensitivity of the tool but also potential refinement of the multilayer deposition process itself such as the combination of nonsmoothing and smoothing deposition processes to avoid the emergence of undetectable defects.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity-Limiting Factors of at-Wavelength Extreme Ultraviolet Lithography Mask Blank Inspection

Tezuka¹,

Tanaka²,

Terasawa³

et al. 2006

jjap

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Sensitivity-limiting factors of at-wavelength inspection for extreme UV lithography (EUVL) mask blanks have been analyzed. The sensitivity of the inspection tool is modeled on the basis of the inspection image of programmed multilayer defects and the characterized attributes of the tool components. The characterization includes point spread function (PSF) analysis of the imaging optics and the back-illuminated charge-coupled-device (BI-CCD) sensor as well as power spectral density (PSD) analysis of the mask blank surface. The statistical scaling of signal-to-noise ratio (SNR) in conjunction with the variables of optics, sensors, and mask blanks has predicted effective improvement paths of its sensitivity. Increasing the magnification of optics, reducing the total PSF, and improving the roughness of mask blanks will address the needs for its application in future generations. Signal intensity dependency on the geometrical attributes of defects is also studied by both experiment and electromagnetic simulation. It is revealed that the bottom height of defects and defect smoothing throughout the multilayer deposition significantly influence defect signal intensity. Comprehensive measures to accommodate a variety of defects and to mitigate associated risks are also discussed.

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Rigorous simulation of defective EUV multilayer masks

Cited by 5 publications

References 6 publications

Actinic detection of multilayer defects on EUV mask blanks using LPP light source and dark-field imaging

Actinic detection of multilayer defects on EUV mask blanks using LPP light source and dark-field imaging

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

Sensitivity-Limiting Factors of at-Wavelength Extreme Ultraviolet Lithography Mask Blank Inspection

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