Inspection of EUV reticles

Pettibone, Donald W.; Veldman, Andrei; Liang, Ted; Stivers, Alan R.; Mangat, Pawitter J. S.; Hector, Scott Daniel; Wasson, James R.; Blaedel, Kenneth L.; Fisch, Emily; Walker, David M.

doi:10.1117/12.472311

Cited by 11 publications

(9 citation statements)

References 3 publications

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“…TaN is more promising than Cr at this point because mask have been made with higher contrast for inspection with TaN (>90%) than with Cr (>65%). 11,43 TaN is also more highly absorbing than Cr at EUV wavelengths, so absorber stacks with TaN can be 5 to 20 nm thinner than those with antireflective Cr. Yan et al 41 recently showed that absorber layers that have index of refraction near unity perform better than those that have an index significantly smaller than unity.…”

Section: Absorber and Buffer Layer Choicementioning

confidence: 98%

“…Pettibone et al 11 have described how contrast and reflectivity of the absorber affect patterned mask inspection sensitivity. The multilayer surface is fairly reflective at typical inspection wavelengths, 43 so the absorber should have low reflectivity to provide high contrast during inspection.…”

Section: Absorber and Buffer Layer Choicementioning

confidence: 98%

“…Defect requirements for both the front and back surfaces are specified with the most challenging requirement being no defects on the front surface >50-nm PSL equivalent size. As Pettibone et al described, 11 bright field imaging inspection has been used for inspecting substrates for defects. A group of five substrates from one supplier have had 3 to 8 defects on the surface >90 nm as determined by a bright field optical inspection.…”

Section: Mask Substratesmentioning

confidence: 98%

“…The resist pattern is transferred into the absorber layer using reactive ion etching. The patterned absorber layer is inspected with bright field optical microscopy, 11 and defects in the absorber pattern are repaired with FIB repair as described by Liang et al 37 The buffer layer protects the multilayer from the repair process. Since the buffer layer absorbs EUV light, it must be removed from the clear areas of the mask pattern with reactive ion and or wet etching.…”

Section: Mask Patterningmentioning

confidence: 99%

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EUVL masks: requirements and potential solutions

Hector

2002

Emerging Lithographic Technologies VI

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Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. Significant progress has been made in developing mask fabrication processes for EUVL. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor that is coated with Mo/Si multilayers. A SEMI standard is now available for mask substrates. SEMI standards are also being developed for mask mounting, for mask blank multilayers and absorbers and for mask handling and storage. Several commercial suppliers are developing polishing processes for LTEM substrates, and they are progressing toward meeting the requirements for flatness, surface roughness, and defects defined in the SEMI standard.One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. Significant progress has been made in developing mask blank multilayer coating processes with low added defect density. Besides lowering added defect density, methods to reduce defect printability are being developed to effectively enable repair of many defect types. These repair processes might significantly increase yield of EUV mask blanks before defect density is lowered to production targets. Calculations of EUVL mask cost indicate that defect repair processes could allow the initial defect density targets for mask blanks to be relaxed.The mask patterning process for EUVL is nearly the same as that for conventional binary optical lithography masks. EUVL mask patterning efforts are focused on developing the EUV-specific aspects of the patterning process. Eight absorbers have been evaluated against the requirements for EUVL masks, and two absorbers-TaN and Cr--will probably meet the requirements after some further development.

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Section: Absorber and Buffer Layer Choicementioning

confidence: 98%

Section: Absorber and Buffer Layer Choicementioning

confidence: 98%

Section: Mask Substratesmentioning

confidence: 98%

Section: Mask Patterningmentioning

confidence: 99%

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EUVL masks: requirements and potential solutions

Hector

2002

Emerging Lithographic Technologies VI

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“…This provides a contrasted image of the absorber patterns and defects present on top of the mask blank, 4 but this technique is not able to probe the multilayer and image buried defects. 5 Methods based on at-wavelength inspection have already been implemented, and have shown the high potential of this technique. The comparison between at-wavelength bright-field and dark-field measurements shows the advantages and the limits of these two types of techniques.…”

mentioning

confidence: 99%

Highly sensitive detection technique of buried defects in extreme ultraviolet masks using at-wavelength scanning dark-field microscopy

Farys

Schiavone

Polack

et al. 2005

Applied Physics Letters

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A technique to probe defects buried inside extreme ultraviolet (EUV) masks has been implemented using a dark-field microscopy detection setup. Specific samples have been fabricated to evaluate the sensitivity of this technique. They consist of silicon oxide gratings of a few nanometers height, coated with 40 layer pairs of molybdenum-silicon. We observed images with a good contrast on samples with defects as low as 3 nm. However, the imaging mechanism of scanning dark-field microscopy is not linear and can produce image distortions. Conditions of correct imaging have been analyzed, and simulations have been performed that show good agreement with the experimental data. This work opens the way for a better understanding of the capability of at-wavelength inspection technique for EUV mask

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Optical inspection of next generation lithography masks

Pettibone

Stokowski

2004

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

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For the last 5years a joint venture has pursued a research program studying and enhancing the ability of optical inspection tools to meet the inspection needs of extreme ultraviolet (EUV) and other next generation lithographies (NGLs). In this article we present a survey of results we have obtained for patterned inspection of NGL masks. The NGL technologies that we have studied include two electron projection lithographies, EUV, and step and flash imprint lithography (SFIL). We discuss the sensitivity of the inspection tools and mask design factors that affect tool sensitivity. In contrast to conventional photomask inspection, which primarily utilizes transmitted light for inspection, almost all NGL mask inspections are performed in reflected light. Much of the work has been directed towards EUV mask inspection and how to optimize the mask to facilitate inspection. Early EUV masks had an optical contrast of 40% or lower. Our partners have succeeded in making high contrast EUV masks ranging in contrast from 70% to 98%. Die to die and die to database inspections, at a wavelength of 257nm, of EUV masks have been achieved with a sensitivity that is comparable to what can be achieved with conventional photomasks, with a minimum detected defect size of 80nm square defects. We have inspected scattering with angular limitation projection electron-beam masks successfully. Electron-beam stencil masks, such as that used in projection reduction exposure with variable axis immersion lenses, pose a problem in that their high aspect ratio of mask thickness to minimum feature width results in low resolution transmission images. Reflected light images provide high-resolution images suitable for inspection, but will not be sensitive to defects below the inspection surface. We have run inspections on SFIL masks in die to die, reflected light in an effort to provide information concerning possible cumulative damage due to imprinting and to provide feedback on defect densities, types and sizes to improve the masks. Our defect sensitivity on SFIL masks is approximately 100nm, though we cannot run at the highest sensitivity due to large numbers of nonprogrammed defects. We have also used an inspection system, at a wavelength of 364nm, to inspect both unpatterned EUV substrates (no coatings) and blanks (with EUV multilayer coatings), and demonstrated a sensitivity of approximately 100nm to polystyrene latex spheres. This information has helped drive down the defect densities on EUV blanks and substrates by some three orders of magnitude. Extensions of conventional optical lithography have pushed out the introduction of NGL technology to the 33nm or possibly the 22nm node. Mask inspection technology will need substantial improvements in resolution to meet the NGL inspection requirements below the 45nm node.

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Inspection of EUV reticles

Cited by 11 publications

References 3 publications

EUVL masks: requirements and potential solutions

EUVL masks: requirements and potential solutions

Highly sensitive detection technique of buried defects in extreme ultraviolet masks using at-wavelength scanning dark-field microscopy

Optical inspection of next generation lithography masks

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