Diffraction based overlay metrology: accuracy and performance on front end stack

Leray, Philippe; Cheng, Stone; Kandel, Daniel; Adel, Mike; Marchelli, Anat; Vakshtein, Irina; Vasconi, Mauro; Salski, Bartłomiej

doi:10.1117/12.772516

Cited by 23 publications

(15 citation statements)

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“…The interested reader is referred Leray et al 18 19 and later by Ausschnitt 20 , any non-zero diffraction order can also be used for overlay measurement. In this case we cannot utilize the reciprocity principle to simplify the model and it remains as described by a whole set of terms from Eqn.…”

Section: Order Control In Scatterometry Overlay Metrologymentioning

confidence: 99%

Diffraction order control in overlay metrology: a review of the roadmap options

et al. 2008

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Resolution enhancement in advanced optical lithography will reach a new plateau of complexity at the 32 nm design rule manufacturing node. In order to circumvent the fundamental optical resolution limitations, ultra low k 1 printing processes are being adopted, which typically involve multiple exposure steps. Since alignment performance is not fundamentally limited by resolution, it is expected to yield a greater contribution to the effort to tighten lithographic error budgets. In the worst case, the positioning budget usually allocated to a single patterning step is divided between two. A concurrent emerging reality is that of high order overlay modeling and control. In tandem with multiple exposures, this trend creates great pressure to reduce scribeline target real estate per exposure. As the industry migrates away from metrology targets formed from large isolated features, the adoption of dense periodic array proxies brings improved process compatibility and information density as epitomized by the AIM target 1 . These periodic structures enable a whole range of new metrology sensor architectures, both imaging and scatterometry based, that rely on the principle of diffraction order control and which are no longer aberration limited. Advanced imaging techniques remain compatible with side-by-side targets while scatterometry methods require grating-over-grating targets. In this paper, a number of different imaging and scatterometry architectures are presented and compared in terms of random errors, systematic errors and scribespace requirements. It is asserted that an optimal solution must combine the TMU peak performance capabilities of scatterometry with the cost of ownership advantages of target size and multi-layer capabilities of imaging. INTRODUCTIONBrightfield imaging has been the mainstay sensor architecture of overlay metrology since the inception of automated methods in the 1980s. Throughout this period, the vast majority of measurements have been performed on so called boxin-box targets, which can be conveniently described as "large and isolated" test structures. By virtue of their smoothly varying centralized pupil distribution functions, such structures present well understood imaging challenges to the metrology tool designer. However, the features of interest for which today's advanced processes are optimized and the distances between them are rapidly shrinking away from the lumbering dimensions of these structures. This is burdening the process engineer with major compatibility challenges between metrology and device structures.At the outset of the 32 nm design rule era, these trends are driving the emergence of a whole new generation of overlay metrology structures, which are at various stages of industry adoption. The majority of these new structures differ fundamentally from their box-in-box predecessors in the crucial metrics of information content and feature density. They are enabled by replacing isolated structures from two patterning steps with periodic ones, either side-by-side or gratin...

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Section: Order Control In Scatterometry Overlay Metrologymentioning

confidence: 99%

Diffraction order control in overlay metrology: a review of the roadmap options

et al. 2008

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“…where M(x,y) is the Mueller matrix of the sample in laboratory (x,y) frame, M(s,p) is the Mueller matrix of the sample in the (s,p) frame and R(φ) is the matrix of rotation in Stokes vector space 5 . The imaging in conoscopic mode implies that all parallel beams reflected with the polar angle θ with the incidence plane at azimuthal angle φ contribute to the same pixel of the image in back focal plane (see Fig.…”

Section: Experimental Set-upmentioning

confidence: 99%

Overlay measurements by Mueller polarimetry in the back focal plane

Novikova¹,

Fallet

Manhas

et al. 2011

SPIE Proceedings

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Angle resolved Mueller polarimetry implemented as polarimetric imaging of the back focal plane of a high NA microscope objective has already demonstrated a good potential for CD metrology 1 . In this paper we present the experimental and numerical results which indicate that this technique may also be competitive for measurements of the overlay error δ between two gratings at different levels. Series of samples of superimposed gratings with well controlled overlay errors have been manufactured and measured with the angle resolved Mueller polarimeter. The overlay targets were 20 µm wide. When overlay error δ = 0 the absolute value of Mueller matrix elements is invariant by matrix transposition. This symmetry breaks down when δ ≠ 0. As a result, we can define the following overlay estimator matrix: Ε = |Μ | − |Μ | t . The simulations show that matrix element E 14 is the most sensitive to the overlay error. In the experiments the scalar estimator of E 14 was defined by averaging the pixel values over specifically chosen mask. The scalar estimator is found to vary essentially linearly with δ for the overlay values up to 50 nm. Our technique allows entering quite small overlay marks (down to 5 µm wide). The only one target measurement is needed for each overlay direction. The actual overlay value can be determined without detailed simulation of the structure provided the two calibrated overlay structures are available for each direction.

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“…This would be particularly true for overlay (default of positioning of superimposed grids at different layers), a parameter that is becoming increasingly critical and requires in-die, dense sampling, while current methods involve up to eight standard (50 μm wide) targets to provide all the relevant information. 45 We provide two examples: The first illustrates the use of spectroscopic measurements, and the second shows the possibilities of the angle-resolved polarimeter.…”

Section: Introductionmentioning

confidence: 99%

Application of Spectroscopic Ellipsometry and Mueller Ellipsometry to Optical Characterization

et al. 2013

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This article provides a brief overview of both established and novel ellipsometry techniques, as well as their applications. Ellipsometry is an indirect optical technique, in that information about the physical properties of a sample is obtained through modeling analysis. Standard ellipsometry is typically used to characterize optically isotropic bulk and/or layered materials. More advanced techniques such as Mueller ellipsometry, also known as polarimetry in the literature, are necessary for the complete and accurate characterization of anisotropic and/or depolarizing samples that occur in many instances, both in research and in real-life activities. In this article, we cover three main subject areas: Basic theory of polarization, standard ellipsometry, and Mueller ellipsometry. The first section is devoted to a short, pedagogical introduction of the formalisms used to describe light polarization. The second section is devoted to standard ellipsometry. The focus is on the experimental aspects, including both pros and cons of commercially available instruments. The third section is devoted to recent advances in Mueller ellipsometry. Application examples are provided in the second and third sections to illustrate how each technique works.

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Diffraction based overlay metrology: accuracy and performance on front end stack

Cited by 23 publications

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Diffraction order control in overlay metrology: a review of the roadmap options

Diffraction order control in overlay metrology: a review of the roadmap options

Overlay measurements by Mueller polarimetry in the back focal plane

Application of Spectroscopic Ellipsometry and Mueller Ellipsometry to Optical Characterization

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