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Fourier ellipsometry - An ellipsometric approach to Fourier scatterometry
Abstract and Figures
An extension of Fourier scatterometry is presented, aiming at increasing the sensitivity by measuring the phase difference between the
reflections polarized parallel and perpendicular to the plane of incidence. The ellipsometric approach requires no additional hardware
elements compared with conventional Fourier scatterometry. Furthermore, incoherent illumination is also sufficient, which enables spectroscopy
using standard low-cost light sources.
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... This configuration, in combination with simulations, results in determining the geometrical properties of nanostructures with resolutions as high as 3 nm and over large areas. This approach distinguishes itself from other works in the literature on Fourier scatterometry, in which the phase difference properties are investigated using a focused beam spot [11][12][13]. ...
... This technique is based on Fourier microscopy and quantifies the intensity and the angle of diffracted orders that are generated by illuminating a grating at well-defined angles of incidence. Unlike other Fourier scatterometry methods described in literature, which use a focused beam spot, this technique uses a collimated laser beam (405 nm) that illuminates the nanostructures (inspection diameter 100 µm) through an objective lens (achromat, numerical aperture (NA) 0.8, working distance 0.3 µm) [11][12][13]19]. This collimated illumination is realized by focusing the incident laser beam in the back-focal plane of the objective lens. ...
Substrate Conformal Imprint Lithography (SCIL) technology enables the fabrication of complex nanostructures with sub-10 nm resolution over large areas for industrial-scale production. This technology utilizes novel composite silicone rubber stamps that provides versatility in addition to high precision. To inspect the quality and reproducibility of the nanostructures that are fabricated using SCIL, a novel optical characterization method using Fourier microscopy is proposed. In this method, nanostructures are illuminated under a microscope objective using a collimated light beam at different incident angles and the properties of the reflected and/or diffracted beams are analysed to extract critical dimensions of the nanostructures. This fast and non-destructive method has the potentials of being used as an in-line inspection technology to extract the critical dimensions of the nanostructures over large areas and improve the overall properties of nanostructured surfaces.
... Improved sensitivity has been demonstrated by utilizing a scanning focused spot, 32-38 interferometry 39, 40 or ellipsometry. 23 ...
... 48 The sensitivity of the parameters can be checked by uncertainty analysis. 23,32,49 In case of spectroscopy and characterization of material properties, the parameterization of the dielectric function is a major issue from which a lot of technologically important material properties can be obtained, like for the case of polycrystalline semiconductors. 50, 51 Also in scatterometry, using different wavelengths in a broad range can increase the accuracy, reliability and the number of fit parameters. ...
Indirect optical methods like ellipsometry or scatterometry require an optical model to calculate the response of the system, and to fit the parameters in order to minimize the difference between the calculated and measured values. The most common problem of optical modeling is that the measured structures and materials turn out to be more complex in reality than the simplified optical models used as first attempts to fit the measurement. The complexity of the optical models can be increased by introducing additional parameters, if they (1) are physically relevant, (2) improve the fit quality, (3) don't correlate with other parameters. The sensitivity of the parameters can be determined by mathematical analysis, but the accuracy has to be validated by reference methods. In this work some modeling and verification aspects of ellipsometry and optical scatterometry will be discussed and shown for a range of materials (semiconductors, dielectrics, composite materials), structures (damage and porosity profiles, gratings and other photonic structures, surface roughness) and cross-checking methods (atomic force microscopy, electron microscopy, x-ray diffraction, ion beam analysis). The high-sensitivity, high-throughput, in situ or in line capabilities of the optical methods will be demonstrated by different applications.
... In addition, optical scatterometry is mostly suitable for measuring repetitive dense structures, but infeasible for the measurement of isolated or generally non-periodic structures. To address the challenges or limitations in conventional optical scatterometry, several designs have been presented with the idea of trying to collect the scattering information about the nanostructure under test conditions as much as possible, such as with the goniometric optical scatter instrument [12][13][14], through-focus scanning optical microscopy [15], scatterfield microscopy [16], tomographic diffractive microscopy [17,18], and Fourier scatterometry [19,20]. Recently, we have also developed a novel instrument called the tomographic Mueller-matrix scatterometer (TMS) [21]. ...
The development of necessary instrumentation and metrology at the nanoscale, especially fast, low-cost, and nondestructive metrology techniques, is of great significance for the realization of reliable and repeatable nanomanufacturing. In this work, we present the application of a homemade novel optical scatterometer called the tomographic Mueller-matrix scatterometer (TMS), for the measurement of photoresist gratings. The TMS adopts a dual rotating-compensator configuration and illuminates the nanostructure sequentially under test conditions by a plane wave, with varying illumination directions and records. For each illumination direction, the polarized scattered field along various directions of observation can be seen in the form of scattering Mueller matrices. That more scattering information is collected by TMS than conventional optical scatterometry ensures that it achieves better measurement sensitivity and accuracy. We also show the capability of TMS for determining both grating pitch and other structural parameters, which is incapable by current zeroth-order methods such as reflectometry- or ellipsometry-based scatterometry.
... Using high numerical aperture (NA) lenses, the range of incident and reflected angles can be as large as -64° to 64° using e.g. of a lens of NA = 0.9 with azimuth angles between 0° and 360°. The sensitivity can be increased by extending the instrumentations utilizing phase information by applying a scanning focused spot [7,8], by interferometry or by adding polarization information using ellipsometry [11,12]. ...
Scatterometry is a common tool for the dimensional characterization of periodic nanostructures. In this paper we compare measurement results of two different scatterometric methods: a goniometric DUV scatterometer and a coherent scanning Fourier scatterometer. We present a comparison between these two methods by analyzing the measurement results on a silicon wafer with 1D gratings having periods between 300 nm and 600 nm. The measurements have been performed with PTB’s goniometric DUV scatterometer and the coherent scanning Fourier scatterometer at TU Delft. Moreover for the parameter reconstruction of the goniometric measurement data, we apply a maximum likelihood estimation, which provides the statistical error model parameters directly from measurement data.
Accurate determination of the physical parameters of nanostructures from optical far-field scattering is an important and challenging topic in the semiconductor industry. Here, we propose a novel metrology method to determine simultaneously the height and side-wall angle of a step-shaped silicon nanostructure. By employing an optical singular beam into a typical coherent Fourier scatterometry system, both parameters can be retrieved through analyzing the intensity profile of the far-field scattering pattern. The use of singular beam is shown to be sensitive to slight changes of the parameters of the step. By changing the relative direction between the singularity and structure, the height and side-wall angle can both be retrieved with high precision. This new method is robust, simple, and can provide valuable means for micro-and-nano- metrologies.
Thin films covering large surfaces are used in a very wide range of applications from displays through corrosion resistance, decoration, water proofing, smart windows, adhesion performance to solar panels and many more. Scaling up existing thin film measurement techniques requires a high speed and the redesign of the configurations. The aim of this review is to give an overview of recent and past activities in the area, as well as an outlook of future opportunities. This article is protected by copyright. All rights reserved.
The research on solar cells based on photonic, plasmonic and various nanostructured materials has been increasing in the recent years. A wide range of nanomaterial approaches are applied from photonic crystals to plasmonics, to trap light and enhance the absorption as well as the efficiency of solar cells. The first part of this chapter presents examples on applications that utilize nanostructured materials for photovoltaics. In the second part, ellipsometry related metrology issues are discussed briefly, dividing the topic in two major parts: effective medium and scatterometry approaches.
Methods for solving Maxwell's equations are integral part of optical
metrology and computational lithography setups. Applications require accurate
geometrical resolution, high numerical accuracy and/or low computation times.
We present a finite-element based electromagnetic field solver relying on
unstructured 3D meshes and adaptive hp-refinement. We apply the method for
simulating light scattering off arrays of high aspect-ratio nano-posts and
FinFETs.
Optical scatterometry is the state of art optical inspection technique for quality control in lithographic process. As such, any boost in its performance carries very relevant potential in semiconductor industry. Recently we have shown that coherent Fourier scatterometry (CFS) can lead to a notably improved sensitivity in the reconstruction of the geometry of printed gratings. In this work, we report on implementation of a CFS instrument, which confirms the predicted performances. The system, although currently operating at a relatively low numerical aperture (NA = 0.4) and long wavelength (633 nm) allows already the reconstruction of the grating parameters with nanometer accuracy, which is comparable to that of AFM and SEM measurements on the same sample, used as reference measurements. Additionally, 1 nm accuracy in lateral positioning has been demonstrated, corresponding to 0.08% of the pitch of the grating used in the actual experiment.
Scatterometry is a well-established, fast and precise optical metrology method used for the characterization of sub-lambda periodic features. The Fourier scatterometry method, by analyzing the Fourier plane, makes it possible to collect the angle-resolved diffraction spectrum without any mechanical scanning. To improve the depth sensitivity of this method, we combine it with white light interferometry. We show the exemplary application of the method on a silicon line grating. To characterize the sub-lambda features of the grating structures, we apply a model-based reconstruction approach by comparing simulated and measured spectra. All simulations are based on the rigorous coupled-wave analysis method.
Non-interferometric phase retrieval from the intensity measurements in Coherent Fourier Scatterometry (CFS) is presented using a scanningfocused spot. Formulae to determine the state of polarization of the scattered light and to retrieve the phase difference between overlappingscattered orders are given. The scattered far field is rigorously computed and the functionality of the method is proved with experimentalresults.
Incoherent Optical Scatterometry (IOS) is widely used in semiconductor industry in applications related to optical metrology particularly in grating reconstruction. Recently, Coherent Fourier Scatterometry (CFS) has emerged as a strong alternative to the traditional IOS under suitable condition. When available, phase information is an added advantage in CFS to complement the intensity data. Phase information in the scattered far field is dependent on the structure and the composition of the grating. We derive and discuss the phase information accessible through the CFS. Phase difference between the diffracted orders is computed and the polarization dependent phase sensitivity of the grating parameters are discussed. The results are rigorously simulated and an experimental implementation of CFS demonstrates the functionality of the method. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
In recent times, coherent Fourier scatterometry has been considered as an emerging optical
grating scatterometry technique for semiconductor metrology since it shows large sensitivity
owing to its scanning ability. However, further utilization of coherence is possible by making
additional measurements using the principle of temporal phase-shifting interferometry. In this
paper, through numerical simulation, we show how scanning and interferometry can be
coupled together to improve the sensitivity of coherent Fourier scatterometry, to extend its
range of applicability and to obtain sufficient information to calculate the complex scattering
matrix for all angles of incidences inside the numerical aperture of a microscope objective.
Incoherent Fourier Scatterometry (IFS) is a successful tool for high accuracy nano-metrology. As this method uses only far field measurements, it is very convenient from the point of view of industrial applications. A recent development is Coherent Fourier Scatterometry (CFS) in which incoherent illumination is replaced by a coherent one. Through sensitivity analyses using rigorous electromagnetic simulations, we show that the use of coherence and multiple scanning makes Coherent Fourier Scatterometry (CFS) more sensitive than Incoherent Fourier Scatterometry (IFS). We also report that in Coherent Fourier Scatterometry it is possible to determine the position of the sample with respect to the optical axis of the system to a precision dependent only on the experimental noise.
Ever progressive miniaturization of integrated circuits and breakthroughs in knowledge of biological macromolecules deriving from DNA and protein surface research are propelling ellipsometry, a measurement technique based on phase and amplitude changes in polarized light, to greater popularity in a widening array of applications. Ellipsometry, without contact and non-damaging to samples, is an ideal measurement technique to determine optical and physical properties of materials at the nano scale.