A study on EUV reticle surface molecular contamination under different storage conditions in a HVM foundry fab

Singh, Sherjang; Yatzor, Brett; Taylor, Ron; Wood, O. R.; Mangat, Pawitter J. S.

doi:10.1117/12.2258393

“…We hypothesized that the most likely explanation for contamination would be a thin carbon film growing on top of the multilayer and absorber, based on previous studies of carbon contamination on EUV multilayers and Ta-based absorbers depending on storage conditions and EUV exposure. [4][5][6] Therefore from this point forward, we hold all other parameters constant and adjust only the carbon layer thickness on either the multilayer or absorber when assessing the repeatability of the technique; this assumption allows us to use a simple brute-force search that guarantees convergence to a unique optimal solution (given a fixed initial model and a set of reflectivity measurements). This allows us to quantify changes in the carbon film thickness and the relative phase.…”

Section: Introductionmentioning

confidence: 99%

Picometer sensitivity metrology for EUV absorber phase

Sherwin

¹

,

Cordova

²

,

Miyakawa

³

et al. 2021

J. Micro/Nanopattern. Mats. Metro.

0

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With growing interest in EUV attenuated phase-shift masks due to their superior image quality for applications such as dense contact and pillar arrays, it is becoming critical to model, measure, and monitor the intensity and relative phase of multilayer and absorber reflections. We present a solution based on physical modeling of reflectometry data, which can achieve single picometer phase precision and sensitivity to changes in average film thickness below one atomic monolayer. We measure absorber and multilayer reflectivity to determine thin-film parameters with a multidimensional optimization and then acquire a new measurement of either multilayer or absorber to determine perturbations in surface contamination thickness. While it is difficult to assess the accuracy of the first step, the simplicity of the second step allows us to characterize our sensitivity to changes in contamination thickness. We apply this analysis using an initial set of measurements and repeated measurements after a period of storage. For the multilayer, the total contamination growth was 1068 pm, which occurred almost exclusively during storage (1085 pm) and decreased very slightly during repeated measurements (−17 pm). For the absorber, the behavior was quite different, with a total growth of 126 pm, which occurred much less during storage (28 pm) and primarily during repeated measurements (98 pm). Ultimately, the change in relative phase (absorber minus multilayer) was −0.86 deg for the multilayer and −1.12 deg for the absorber. We estimate the precision of the surface contamination measurement to be 3σ < 6pm for measuring thickness and 3σ < 0.2 deg for measuring phase.

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“…We hypothesized that the most likely explanation for contamination would be a thin carbon film growing on top of the multilayer and absorber, based on previous studies of carbon contamination on EUV multilayers and Ta-based absorbers depending on storage conditions and EUV exposure. [4][5][6] Therefore from this point forward, we hold all other parameters constant and adjust only the carbon layer thickness on either the multilayer or absorber when assessing the repeatability of the technique; this assumption allows us to use a simple brute-force search that guarantees convergence to a unique optimal solution (given a fixed initial model and a set of reflectivity measurements). This allows us to quantify changes in the carbon film thickness and the relative phase.…”

Section: Introductionmentioning

confidence: 99%

Picometer sensitivity metrology for EUV absorber phase

Sherwin

¹

,

Cordova

²

,

Miyakawa

³

et al. 2020

Extreme Ultraviolet Lithography 2020

0

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With growing interest in EUV attenuated phase-shift masks due to their superior image quality for applications such as dense contact and pillar arrays, it is becoming critical to model, measure, and monitor the intensity and relative phase of multilayer and absorber reflections. We present a solution based on physical modeling of reflectometry data, which can achieve single picometer phase precision and sensitivity to changes in average film thickness below one atomic monolayer. We measure absorber and multilayer reflectivity to determine thin-film parameters with a multidimensional optimization and then acquire a new measurement of either multilayer or absorber to determine perturbations in surface contamination thickness. While it is difficult to assess the accuracy of the first step, the simplicity of the second step allows us to characterize our sensitivity to changes in contamination thickness. We apply this analysis using an initial set of measurements and repeated measurements after a period of storage. For the multilayer, the total contamination growth was 1068 pm, which occurred almost exclusively during storage (1085 pm) and decreased very slightly during repeated measurements (−17 pm). For the absorber, the behavior was quite different, with a total growth of 126 pm, which occurred much less during storage (28 pm) and primarily during repeated measurements (98 pm). Ultimately, the change in relative phase (absorber minus multilayer) was −0.86 deg for the multilayer and −1.12 deg for the absorber. We estimate the precision of the surface contamination measurement to be 3σ < 6pm for measuring thickness and 3σ < 0.2 deg for measuring phase.

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“…Molecular contamination can build up on an EUV photomask during storage. Upon subsequent EUV exposure these loosely bound hydrocarbons can be carbonized, leading to EUV photomask reflection loss and degradation of exposure uniformity [6] .…”

Section: Introductionmentioning

confidence: 99%

Lifetime test on EUV photomask with EBL2

Wu

¹

,

Bender

²

,

Jonckheere

³

et al. 2019

Photomask Japan 2019: XXVI Symposium on Photomask and Next-Generation Lithography Mask Technology

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TNO has built EBL2, an EUV exposure facility equipped with an in vacuo X-ray photoelectron spectroscopy setup (XPS) and an in-situ ellipsometer. EBL2 enables lifetime testing of EUV optics, photomasks, pellicles and related components under development in relevant EUV scanner and source conditions, which was previously not available to industry. This lifetime testing can help the industry to prepare for high volume production using EUV lithography by bringing forward information about material behavior which facilitates the development cycle. This paper describes an EUV photomask lifetime test performed at EBL2. The mask was exposed to different EUV doses under a controlled gas and temperature environment. To investigate how EUV light interacts with the mask, various analysis techniques were applied before and after EUV exposure. In-situ XPS was used to investigate elemental compositions of the mask surface. An ex-situ critical dimension scanning electron microscope (CD-SEM) and an atomic force microscope (AFM) were used to explore the impact of EUV light on critical dimensions (CD) and feature profiles. In addition, EUV reflectometry (EUVR) was used to investigate the change of reflectivity after EUV exposures. The exposure conditions are reported, as well as an analysis of the effects observed.

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A study on EUV reticle surface molecular contamination under different storage conditions in a HVM foundry fab

Cited by 3 publications

References 4 publications

Picometer sensitivity metrology for EUV absorber phase

Picometer sensitivity metrology for EUV absorber phase

Picometer sensitivity metrology for EUV absorber phase

Lifetime test on EUV photomask with EBL2

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