Mask aspects of EUVL imaging at 27nm node and below

Davydova, Natalia; Setten, Eelco van; Han, Sang-In; Kerkhof, Mark van de; Kruif, Robert de; Oorschot, Dorothe; Zimmerman, John; Lammers, Ad; Connolly, Brid; Driessen, Frank; Oosten, Anton van; Dusa, Mircea V.; Dommelen, Youri van; Harned, Noreen; Jiang, Jiong; Liu, Wei; Kang, Houyang; Liu, Huayu

doi:10.1117/12.896816

Cited by 13 publications

(11 citation statements)

References 12 publications

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“…A ML stack calibration was already performed in our previous work for other masks [3], [4] and a reasonably good match is achieved for peak reflectivity, centroid wavelength and full width at half maximum of reflectivity spectrum by assuming Mo-Si inter-mixing in the multilayer. However so far we could not achieve good match of the low reflectance tails of the spectrum.…”

Section: Reflectivity Measurements and Stack Calibrationmentioning

confidence: 98%

“…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%

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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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Section: Reflectivity Measurements and Stack Calibrationmentioning

confidence: 98%

Section: Figurementioning

confidence: 99%

Experimental approach to EUV imaging enhancement by mask absorber height optimization

et al. 2013

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“…However absorber height variations will result in varying shadowing effect and thus contribute to CDU. Furthermore where the absorber transmission of a transmissive mask is < 0.1% the EUV absorber reflectivity is 1-3% inducing image border reflections to neighboring fields and resulting in additional CDU [2] . Some parameters are interchangeable.…”

Section: Euv Mask Challengesmentioning

confidence: 98%

EUVL mask performance and optimization

et al. 2012

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d Toppan Photomasks inc., 131 Old Settlers Boulevard, Round Rock, TX 78664 USA EUV lithography requires an exposure system with complex reflective optics and an equally complex EUV dedicated reflective mask. The required high level of reflectivity is obtained by using multilayers. The multilayer of the system optics and the mask are tuned to each other. The mask is equipped with an additional patterned absorber layer.The EUV mask is an optical element with many parameters that contribute to the final image and overlay quality on the wafer and the productivity of the system. Several of these parameters can be tuned for optimal overlay, imaging and productivity results. This should be done with care because of possible interaction between parameters.We will present an overview of the EUV mask contributors to the imaging, overlay and productivity performance for the 27 nm node and below, such as multilayer and absorber stack composition, reflectivity and reflectivity uniformity. These parameters will be reviewed in the context of real-life scanner parameters for the ASML NXE:3100 and NXE:3300 system configurations. The predictions will be compared to actual exposure results on NXE:3100 systems (NA=0.25) for various masks and extrapolated to the NXE:3300 (NA=0.33).In particular, we will present extensive multilayer and absorber actinic spectral reflectance measurements of a state-ofthe art EUV mask over a range of incidence angles corresponding to an NA of 0.33 at multiple positions within the image field. The ML measurements allow calibrating ML stack for imaging simulations. It allows also the estimation of mask-induced apodization effects having impact on overlay.In general, the reflectivity measurements will give detailed variations over the image field of mask parameters such as ML centroid wavelength and absorber reflectivity which contribute to CD uniformity. Such a relation will be established by means of rigorous full stack imaging simulations taking into account optical properties of the coming NXE:3300 system.Based on this investigation we will propose optimal EUV mask parameters for the 22 nm node EUV lithography and below, to provide guidance for mask manufacturers to support the introduction of EUV High Volume Manufacturing.

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“…However, the path toward establishing the EUV lithography faces many technical difficulties. Issues with insufficient light-source power, particlefree mask handling, defect-free mask, availability of flat mask blanks, [1][2][3][4][5] and resist material development 6,7 are some of those difficulties that need to be resolved. From the viewpoint of EUV mask fabrication, mask pattern defect inspection [8][9][10] and repair [11][12][13] are some of the even more demanding tasks to be addressed.…”

Section: Introductionmentioning

confidence: 99%

Observation of phase defect on extreme ultraviolet mask using an extreme ultraviolet microscope

Amano¹,

Terasawa²,

Watanabe³

et al. 2014

J. Micro/Nanolith. MEMS MOEMS

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Abstract. Influences of phase defect structures on extreme ultraviolet (EUV) microscope images were examined. Phase defects on the bottom of a multilayer (ML) do not always propagate vertically upward to the ML's top surface. For this study, two types of masks were prepared. One was an EUV blank with programmed phase defects made of lines in order to analyze the inclination angle of the phase defects. The other was an EUV mask that consists of programmed dot type phase defects 80 nm wide and 2.4 nm high with absorber patterns of halfpitch 88-nm lines-and-spaces. The positions of the phase defects relative to the absorber lines were designed to be shifted accordingly. Transmission electron microscope observations revealed that the line type phase defects starting from the bottom surface of the ML propagated toward the ML's top surface, while inclined toward the center of the EUV blank. At the distances of 0 and 66 mm from the center of the EUV blank, the inclination angles varied from 0 to 4 deg. The impacts of the inclination angles on EUV microscope images were significant even though the positions of the phase defect relative to the absorber line, as measured by a scanning probe microscope, were the same. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Mask aspects of EUVL imaging at 27nm node and below

Cited by 13 publications

References 12 publications

Experimental approach to EUV imaging enhancement by mask absorber height optimization

Experimental approach to EUV imaging enhancement by mask absorber height optimization

EUVL mask performance and optimization

Observation of phase defect on extreme ultraviolet mask using an extreme ultraviolet microscope

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