Mr. Devesh Thakare Profile

Devesh Thakare

at K U Leuven

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Author

Publications (9)

SPIE Journal Paper | 7 August 2023

Optimizing extreme ultraviolet lithography imaging metrics as a function of absorber thickness and illumination source: a simulation case study of Ta-Co alloy

Devesh Thakare, Annelies Delabie, Vicky Philipsen

JM3, Vol. 22, Issue 03, 033201, (August 2023) https://doi.org/10.1117/12.10.1117/1.JMM.22.3.033201

KEYWORDS: Diffraction, Nanoimprint lithography, Light sources and illumination, Alloys, Extreme ultraviolet lithography, Extreme ultraviolet, Optical properties, Semiconducting wafers, Reflection, Printing

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BackgroundThe optical properties of the absorber material and its thickness, along with the choice of illumination, govern the imaging performance of an EUV photomask. Consequently, the imaging metrics, viz., normalized image log slope (NILS), telecentricity error (TCE), and best focus variation (BFV) through pitch, exhibit a trade-off. Previous studies have focused on either reflectivity or phase shift induced by the absorber to determine the optimum absorber thickness, which ignores the structure of the patterns on the mask.AimThis simulation study intends to facilitate the optimum absorber thickness selection with an emphasis on diffraction order analysis of the line and space (LnS) pattern and investigates the impact of illumination source shapes for a Ta-Co alloy absorber mask.ApproachWe investigate the behavior of imaging metrics as a function of the absorber thickness using literature-recommended illumination source shapes. NILS, TCE, throughput criterion, diffraction order’s amplitude ratio, and phase difference are the critical parameters when selecting the optimum absorber thickness. A through-pitch imaging performance of the Ta-Co alloy absorber with recommended thicknesses is compared with the reference 60 nm Ta-based absorber using leaf dipole (LDP), inner half leaf dipole (IHLDP), and outer half leaf dipole (OHLDP) for LnS patterns with a target trench of 10 nm and pitch ranging from 20 to 40 nm.ResultsThe proposed absorber thickness optimization methodology validates the reference Ta-based absorber thickness and recommends 52 nm of Ta-Co alloy absorber thickness. IHLDP and OHLDP demonstrate enhanced NILS for the smallest pitch. However, this behavior is inconsistent throughout the pitch. IHLDP exhibits low TCE. However, because of higher BFV, the advantages are not exceptionally beneficial.ConclusionsA holistic approach makes the proposed absorber thickness optimization methodology reliable and generally applicable. The through-pitch simulation outcomes at selected absorber thickness favor a conventional full-leaf dipole for the studied imaging metrics.

SPIE Journal Paper | 21 June 2023

Evaluation of Ta-Co alloys as novel high-k extreme ultraviolet mask absorber

Devesh Thakare, Meiyi Wu, Karl Opsomer, Qais Saadeh, Victor Soltwisch, Philipp Naujok, Christophe Detavernier, Davide Dattilo, Markus Foltin, Andy Goodyear, Mike Cooke, Annelies Delabie, Vicky Philipsen

JM3, Vol. 22, Issue 02, 024403, (June 2023) https://doi.org/10.1117/12.10.1117/1.JMM.22.2.024403

KEYWORDS: Alloys, Extreme ultraviolet, Tantalum, Nanoimprint lithography, Etching, Oxides, Silicon, Ruthenium, Light sources and illumination, Film thickness

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Proceedings Article | 1 December 2022 Paper

Precise optical constants: determination and impact on metrology, simulation, and development of EUV masks

Qais Saadeh, Hazem Mesilhy, Victor Soltwisch, Andreas Erdmann, Richard Ciesielski, Leonhard Lohr, Anna Andrle, Vicky Philipsen, Devesh Thakare, Christian Laubis, Frank Scholze, Michael Kolbe

Proceedings Volume 12293, 122930Y (2022) https://doi.org/10.1117/12.2643246

KEYWORDS: Extreme ultraviolet, Scatterometry, Photomasks, Refractive index, Scattering, Reflectivity, Metrology, Databases, Oxidation, Multilayers, Extreme ultraviolet lithography, Extreme ultraviolet coatings, Modeling and simulation, Optical constants, Optical metrology

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Proceedings Article | 1 November 2022 Paper

Optimizing EUV imaging metrics as a function of absorber thickness and illumination source: simulation case study of Ta-Co alloy

Devesh Thakare, Annelies Delabie, Vicky Philipsen

Proceedings Volume 12472, 124720A (2022) https://doi.org/10.1117/12.2640098

KEYWORDS: Photomasks, Extreme ultraviolet lithography

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Proceedings Article | 15 September 2022 Presentation

The EUV mask exposed

Vicky Philipsen, Devesh Thakare, Dongbo Xu, Ling Ee Tan, Jetske Stortelder, Mike Cooke, Andy Goodyear, Victor Soltwisch, Qais Saadeh, Sascha Brose, Andreas Erdmann

Proceedings Volume PC12325, PC123250B (2022) https://doi.org/10.1117/12.2641306

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Proceedings Article | 26 May 2022 Presentation + Paper

Evaluation of Ta-Co alloys as novel high-k EUV mask absorber

Devesh Thakare, Meiyi Wu, Karl Opsomer, Christophe Detavernier, Philipp Naujok, Qais Saadeh, Victor Soltwisch, Annelies Delabie, Vicky Philipsen

Proceedings Volume 12051, 120510D (2022) https://doi.org/10.1117/12.2614235

KEYWORDS: Tantalum, Extreme ultraviolet, Photomasks, Cobalt, Extreme ultraviolet lithography

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Proceedings Article | 12 October 2021 Presentation + Paper

First results of EUV-scanner compatibility tests performed on novel 'high-NA' reticle absorber materials

Jetske Stortelder, Rob Ebeling, Corné Rijnsent, Michel van Putten, Véronique de Rooij-Lohmann, Maximilian Smit, Arnold Storm, Norbert Koster, Henk Lensen, Vicky Philipsen, Karl Opsomer, Devesh Thakare, Torsten Feigl, Philipp Naujok

Proceedings Volume 11854, 1185414 (2021) https://doi.org/10.1117/12.2600928

KEYWORDS: Extreme ultraviolet lithography, Hydrogen, Reticles, Extreme ultraviolet, Plasma, Scanners, EUV optics, Accelerated life testing, Materials analysis, Extreme ultraviolet coatings, Contamination control

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Novel reticle absorber materials are required for high-NA EUV lithography. TNO and ASML developed an assessment for the compatibility of novel high-NA reticle absorber materials with conditions that mimic the EUV scanner environment^[1]. Four candidate reticle absorber materials were evaluated, TaCo, RuTa, PtMo and Pt2Mo alloys, in a joint research program. For the compatibility tests, dedicated samples with silicon wafer substrates were fabricated. The silicon wafers were coated with a Mo-Si multilayer coating, followed by a Ru capping layer and finally the absorber material.

Chemical outgassing tests, in presence of hydrogen radicals, did not show chemical outgassing for the TaCo and PtMo alloys. RuTa and Pt₂Mo alloys were not tested, based upon their elemental composition chemical outgassing is not expected. Next, all four materials were exposed in a hydrogen plasma resistance test equivalent to an EUV exposure of at least 250 thousand wafers** in the EUV scanner. No plasma-induced defects, like blistering or delamination, were found that were related to the intrinsic absorber properties.

The RuTa and PtMo alloys were selected for EUV exposure in the EBL2 facility at TNO. Both materials were exposed to an 9.6 kJ/mm² EUV peak dose at an EUV peak intensity of 450 mW/mm² in a hydrogen environment. This EBL2 EUV exposure of 6 hours represents about 1-2 months of EUV dose (at least 150 thousand wafers) in a NXE or EXE scanner with a 300 W source. Both materials showed good performance during EUV exposure. Relevant surface defects and chemical outgassing were not observed. The few observed blisters in the low EUV intensity areas are likely provoked by particle contamination or coating defects.

All four absorber materials, TaCo, RuTa, PtMo and Pt₂Mo alloys performed well in the compatibility tests that were executed. Not all compatibility tests could be performed on each absorber material within the scope of our research program. Further testing would be needed to complete the compatibility assessment, including an EUV exposure on a patterned reticle.

SPIE Journal Paper | 3 May 2021

Study of novel EUVL mask absorber candidates

Meiyi Wu, Devesh Thakare, Jean-François de Marneffe, Patrick Jaenen, Laurent Souriau, Karl Opsomer, Jean-Philippe Soulié, Andreas Erdmann, Hazem M. Mesilhy, Philipp Naujok, Markus Foltin, Victor Soltwisch, Qais Saadeh, Vicky Philipsen

JM3, Vol. 20, Issue 02, 021002, (May 2021) https://doi.org/10.1117/12.10.1117/1.JMM.20.2.021002

KEYWORDS: Photomasks, Extreme ultraviolet lithography, Extreme ultraviolet, Nanoimprint lithography, Etching, Ruthenium, Refractive index, Optical lithography, Semiconducting wafers, Thin films

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Novel mask absorber designs are catching the attention of the EUVL community due to their ability to mitigate mask 3D effects. Material selection is part of such an optimization. We propose several candidates as novel EUV lithography mask absorbers, namely TaTeN, Ru–Ta, and Pt–Mo alloys. The choice of these materials is based on their theoretical performance evaluated by EUV imaging simulation based on their complex refractive index N ( λ ) = n ( λ ) + ik ( λ ) , where the optical constants n and k relate to the phase velocity and the absorption of electromagnetic radiation with a wavelength λ, respectively. The materials are deposited as thin films on Si substrate with an additional Ru layer to mimic the cap of the multilayer mirror on the real mask. The experimental n and k values are determined by analyzing EUV reflectivity data obtained using a 13.5-nm synchrotron EUV radiation. The imaging simulation presented consists of calculating several imaging metrics including non-telecentricity, normalized image log-slope, and threshold-to-size for specific use cases using the novel absorber. It also compares the proposed materials with the reference TaBN absorber. TaTeN shows higher absorption than TaBN and refraction closer to 1, which improves phase matching for a high k absorber. The refractive index of Ru–Ta and Pt–Mo alloys exhibits a large difference from that of air and provides the required phase shift of attenuated phase shift masks. The characterizations of these materials target the requirements of an EUVL mask: durability for mask cleaning, mask lifetime, and etchability for mask patterning. The stability is first tested against several standard mask cleaning solutions by a beaker test for up to 24 h. The samples are also exposed to hydrogen plasma to imitate the working environment in an EUV scanner. Concerning material patterning, chemical reactive ion etch is applied for preliminary tests. A proper etch recipe is found for TaTeN with a good etch rate (about 60 nm / min) and good selectivity to the Ru underlayer (Ru etch is negligible).

Proceedings Article | 20 October 2020 Presentation + Paper

Mask absorber for next generation EUV lithography

Meiyi Wu, Devesh Thakare, Jean-François de Marneffe, Patrick Jaenen, Laurent Souriau, Karl Opsomer, Jean-Philippe Soulié, Andreas Erdmann, Hazem Mesilhy, Philipp Naujok, Markus Foltin, Victor Soltwisch, Qais Saadeh, Vicky Philipsen

Proceedings Volume 11517, 1151706 (2020) https://doi.org/10.1117/12.2572114

KEYWORDS: Photomasks, Extreme ultraviolet lithography, Extreme ultraviolet, Etching, Ruthenium, X-rays, Refractive index, Reflectivity, Phase shifts, Mask cleaning

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Novel mask absorber designs are calling attention of the EUVL community due to their ability to mitigate mask 3D effects. Material selection is part of such optimization [1]. In this paper we propose several candidates as novel EUV lithography mask absorbers, namely TaTeN, Ru-Ta and Pt-Mo alloys. The choice of these materials is based on their theoretical performance evaluated by EUV imaging simulation based on their complex refractive index N(λ) = n(λ) +ik(λ), where the optical constants n and k relate to the phase velocity and to the absorption of an electromagnetic radiation with a wavelength λ, respectively. The materials are deposited as thin films on Si substrate with an additional Ru layer to mimic the cap of multilayer mirror (MLM) on the real mask. The experimental n and k values are determined by analyzing EUV reflectivity data obtained using a 13.5 nm synchrotron EUV radiation. The imaging simulation presented in this paper consists of calculation of several imaging metrics like non-telecentricity, normalized image log-slop (NILS), and threshold-to-size for specific use cases using the novel absorber. It also compares the proposed materials to the reference TaBN absorber. TaTeN shows higher absorption than TaBN and refraction closer to 1, which improves phase matching for a high k absorber. The refractive index of Ru-Ta and Pt-Mo alloys exhibits a large difference to that of air and provides the required phased shift of attenuated phase shift masks [2]. The characterizations of these materials target the requirements of an EUVL mask: durability for mask cleaning, mask lifetime and etchablity for mask patterning. The stability is first tested against several standard mask cleaning solutions by beaker test up to 24 hours with the film structure monitored by X-ray reflectivity analysis. The samples are also exposed to hydrogen plasma to imitate the working environment in a EUV scanner. Material integrity is checked with Rutherford backscattering spectroscopy before and after the exposure. Concerning material patterning, chemical reactive ion etch is applied for preliminary tests. A proper etch recipe is found for TaTeN with good etch rate (about 60 nm/min) and good selectivity to Ru underlayer (Ru etch is ignorable).

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