Imaging performance improvements by EUV mask stack optimization

Davydova, Natalia; Setten, Eelco van; Kruif, Robert de; Oorschot, Dorothe; Dusa, Mircea V.; Wagner, Christian; Jiang, Jiong; Liu, Wei; Kang, Houyang; Liu, Huayu; Spies, Petra; Wiese, N.; Waiblinger, M.

doi:10.1117/12.884504

Cited by 9 publications

(14 citation statements)

References 4 publications

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“…Based on literature we know that intermixing between the Si and Mo layers will happen [2,6]. Table 2 presents the details of a ML with intermixing from [6]. The intermixing layers formed by Mo atoms deposited on Si are thicker than those formed by Si atoms incident upon Mo [8][9][10].…”

Section: Starting Pointmentioning

confidence: 98%

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Actinic characterization and modeling of the EUV mask stack

Philipsen¹,

Hendrickx

Jonckheere

et al. 2013

SPIE Proceedings

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This paper presents a detailed mask stack modeling based on experimental actinic characterization of the EUV mask stack. A dedicated mask has been fabricated with line/space gratings down to 40nm half-pitch (at mask level, i.e., 10nm at wafer). Using the Advanced Light Source facility at LBNL extensive reflectometry and diffractometry have been performed. The experimental reflectivity results through incidence angle and through EUV wavelength enable us to model both the multilayer definition, as well as the absorber definition in the simulator. The effective performance of the calibrated mask stack in the simulator is validated against the experimental diffractometry results through incidence angle. The presented experimental mask stack characterization and modeling allows a better definition of the mask stack in the simulation tools to enhance their predictive and precompensation power.

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Section: Starting Pointmentioning

confidence: 98%

“…Also the simulated curve does not match to the experimental one. Based on literature we know that intermixing between the Si and Mo layers will happen [2,6]. Table 2 presents the details of a ML with intermixing from [6].…”

Section: Starting Pointmentioning

confidence: 99%

Actinic characterization and modeling of the EUV mask stack

Philipsen¹,

Hendrickx

Jonckheere

et al. 2013

SPIE Proceedings

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“…The reflectance of the absorber decreases with absorber height, thus the image contrast and NILS (normalized image log-slope) increase (Figure 4). A high contrast image is less sensitive to dose variation and has larger Exposure Latitude (EL) [2], [3] and larger Process Window (PW). A high-contrast image is also less sensitive to variations of scanner parameters such as aberrations, dynamics etc., therefore the Critical Dimension Uniformity (CDU) of a high contrast image is also better.…”

Section: Figurementioning

confidence: 99%

“…MEEF typically decreases if the image contrast is increased, but for larger absorber heights, wafer CD is more sensitive to mask CD variations. Therefore MEEF behavior as a function of absorber height is non-trivial [2] .…”

Section: Figurementioning

confidence: 99%

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Experimental approach to EUV imaging enhancement by mask absorber height optimization

et al. 2013

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EUV lithography performance is improved significantly by optimizing and fine-tuning of the EUV mask. The EUV mask is an active element of the scanner optical system influencing main lithographic figure of merits such as image contrast, critical dimension uniformity (CDU), focus and overlay. The mask stack consists of Mo/Si multilayer acting as a bright field and a patterned absorber stack. In this work we will concentrate on investigation of EUV absorber.Absorber topography that is pronounced compared to the imaging wavelength of 13.5 nm, will give rise to various mask 3d effects such as shadowing or dependence of CD on feature orientation, best focus shift of different resolution structures, etc. [1] [2] . Light interference in the absorber layer results in swinging behavior of various lithography metrics as function of the absorber height [5] . Optimization of the mask absorber allows mitigating mask 3d effects and improving imaging performance. In particular, reduction of the absorber height mitigates the shadowing effect and relaxes requirements on Optical Proximity Correction (OPC), but can result in smaller Process Window due to lower imaging contrast and larger best focus shifts.In this work we will show results of an experimental approach to absorber height optimization. A special mask with 27 different absorber heights in the range 40-70 nm is manufactured by Toppan Photomasks. EUV reflectivity spectra are measured for the different absorber heights and an experimental swing curve is constructed.For each absorber height various resolution features are present on the mask. Lines of 27 nm and 22 nm are imaged on the wafer using the ASML EUV scanner NXE:3300B with an NA of 0.33. The experimental CD swing curve is constructed as well as HV change as a function of absorber height. The impact of the absorber height on Exposure Latitude (EL) and Dose to Size (D2S) is investigated. EL improves with increasing absorber height in some cases, however there is no clear EL gain for a 70 nm absorber compared to for example 52 nm absorber. D2S does show a clear trend through absorber height. In particular, D2S can be reduced by absorber height reduction: e.g. for 52 nm absorber D2S is 5% or 1 mJ/cm 2 smaller compared to 70 nm.The experimental results are used for calibration and verification of rigorous mask 3d simulations. This knowledge is crucial for accurate OPC of production masks and allows for accurate litho simulations of EUV user cases as a basis for lithography roadmaps towards High Volume Manufacturing and High NA EUV.EUV absorber behavior is determined by phase shifts Reflectivity Swing Curve X 8% k 6% 4% 2% awrmiim mm 55 6.5 75 85 9.5 10.5 Ab orbe heieht,A /2n Light retardation in the matter 4 phase shift Substrate: LTEM EUV mask n -refraction index of absorber 46, 53, 60, 67.5, 75, 82 (for n = 0.95) 180° phase shift between bright field and dark field: A h 67.5 (for n=0.95) 1. Figure 1 Two types of phase shifts in EUV mask: (a) Interference between reflection at the top of the absorber and from the multil...

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