In the semiconductor manufacturing, the control of Chemical-Mechanical Planarization (CMP) process time for Shallow Trench Isolation (STI) is important. A wafer under- or over-polishing causes leakage and short-circuits making the chips defective. The CMP process control by interferometry is one of the most used systems to monitor the polishing time. In some cases, the interferometry process control is not possible because the wafer patterns cause some unwanted effects such as scattering, diffraction, and absorption. Consequently the signal is affected. In this paper, we apply a theoretical and experimental approach on the light reflected from different STI stacks in order to interpret the observed optical phenomenon. The experimental study is done to get close to the light measurement conditions within the manufacturing environment. With this experiment, we evidence that the trench pattern inside memory zones is responsible for the diffraction effect on the signal. In a production environment, this pattern results in a lower measured intensity when the size of memory area increases. Besides, numerical calculations are performed based on differential method in order to predict the diffracted intensity, which depends on the chip design parameters and the incident wavelengths tuning. By using STI models, this method helps to determine the wavelengths with the highest reflected intensity.
The suitability of a corneal graft for transplant surgery is based on different criteria. It may be rejected in particular due
to a loss of transparency, directly linked to its scattering properties. Then, these become an important parameter. The aim
of this paper is to quantify the influence of the cornea thickness and of the epithelial layer on scattering properties. The
origin of scattering is discussed based on polarimetric analysis of scattered field (surface and/or bulk) and on full-field
optical coherence tomography imaging (structural information).
The cornea is the single human tissue being transparent. This unique property may be explained by the particular
structure of the cornea, but the precise role of each of its constituents remains unsolved. On other matter, prior to corneal
transplant, graft must be evaluated during a sorting procedure where a technician assesses of its transparency quality.
Nevertheless, this criterion remains subjective and qualitative.
This study proposes to combine 3D imagery using Full-Field Optical Coherence Tomography jointly with angular
resolved scattering measurement to achieve a quantitative transparency characterization of the cornea. The OCT provides
micrometric resolution structural information about the cornea, and we observe the evolution occurring when oedema
develops within the tissue. Scattering properties are evaluated and compared parallely, as the transparency of the graft.
A close link between the scattering intensity level of the cornea and its thickness is highlighted through this study.
Furthermore, the three-dimensional imagery offers a view over the structural modifications leading to a change in
transparency, and the combination with scattering properties measurement provides clues over the characteristic scale of
scatterers to consider for a better understanding of corneal transparency evolution.
Achieving an objective and quantified parameter for the transparency would be helpful for a more efficient corneal graft
sorting, and may be able to detect the presence of localized wounds as the ones related to a previous refractive surgery.
However, the study of graft nearly eligible for corneal transplant would be needed to confirm the results this study
presents.
With device size reduction, variability induced by local micro roughness is becoming less and less negligible in terms of
statistical control of critical dimensions (CD). We applied a recent approach developed at Fresnel Institute for the
determination of micro roughness on periodic structures through optical far field characterization using an angle resolved
scatterometer. Structure periodicity affects the diffraction orders, while roughness signature is mainly found between
diffraction orders. Theoretical simulation was performed using two in-house computer codes based on differential
method and on first order approximation. We will review the theoretical approach and show roughness data derived from
measurement on glass gratings as well as poly silicon gate type structures.
In the field of microelectronic industry, periodic structures are produced with spatial dimensions that can be less than
100 nm. Because of the material and process effects, these structures will most likely present some additional roughness.
The optical far field characterization of these structures usually allows to deduce the shape parameters of the periodic
structure. Measurements are performed thanks to an ellipsometric apparatus, associated with modelling and inversion
algorithms. In this configuration the technique is called "scatterometry". This method does not permit to directly extract
roughness parameters. This paper aims at describing how model and experimental tools can be used to characterize the
roughness of gratings. The study needs a complete three-dimensional electromagnetic modelling of the structure but the
calculations are very time consuming. Here, different theoretical models are associated in order to reduce the calculation
time: rigorous numerical differential theory and Born approximation theory. The exact numerical model allows to treat
the periodic part of the structure while the roughness is viewed as a perturbation and treated using a first order
approximation. From an experimental point of view, the information on the periodic part of the structure lies in the
diffraction orders, while the roughness signature is mainly found between diffraction orders. Practically, this model
could be used in the semiconductor industry for a detailed roughness characterization, based on an optical measurement
using the same test structures used for scatterometry.
Micrometer scale resolution full-field optical coherence tomography (FF-OCT) is developed for imaging human graft corneas. Three-dimensional (3-D) images with ultrahigh resolution (respectively, 1 and 1.5 µm in the axial and transverse directions), comparable to traditional histological sections, are obtained allowing the visualization of the cells and the precise structure of the different layers that compose the tissue. The sensitivity of our device enables imaging the entire thickness of the cornea, even in edematous corneas more than 800 µm thick. Furthermore, we provide tomographic 3-D images of laser incisions inside the tissue at various depths without slicing the studied corneas. The effects of laser ablations can be observed, along various optical sections, directly in the bulk of the sample with high accuracy, providing information on the interface quality and also imaging tiny changes of the tissue structure. FF-OCT appears to be a powerful tool for subcellular imaging of the corneal structure and pathologies on the entire thickness of the tissue as well as interface quality and changes in the collagen structure due to laser incisions on ex vivo human cornea.
Angle-resolved ellipsometric data are recorded on light scattering and provide a real time process for selective imaging
in scattering media. Surface and bulk effects are separated and could be used for a selective screening inside the tissues.
Optical Coherence Tomography (OCT) is an attractive technique to study works of art because it allows non-destructive
and contactless analysis. In the case of musical instruments, the study of wood finishes could give interesting
information as the thicknesses of the layers, the number of layers and the presence of fillers. A time-domain full-field
OCT, achieving high resolution, is used in both visible and near infrared ranges to characterize semi-transparent layers
containing scattering particles as charged varnish layers. We present OCT measurements on wood varnished with
different coatings. We show that the detection of pigment particles is dependent of the spectral range and that both
spectral domains allow to reach micrometer-scale spatial resolutions.
Light scattering is a current tool for characterization of defects in optical interferential coatings. However, this tool is not fully efficient for multilayer component. Indeed, in this case, the scattered light from multilayers originates from several interface roughnesses that cannot be separated a priori. In this paper, a technique which can isolate a single interface embedded within a stack is presented. It is based on destructive interferences between the polarization modes of the angular scattering. These interferences can be tuned in a selective way that allows the extraction of light issued from a specific scattering interface.
A recent optical technique is reviewed to identify the scattering origins (surface roughness or bulk heterogeneities) and
eliminate scattering sources in a selective way. Applications concern the field of optical interference coatings, remote
sensing and imaging in random media.
Far field light scattering from rough surfaces and inhomogeneous bulks has extensively been studied these last decades, with a major application in random media characterization. Angular Resolved measurements are performed and investigated thanks to the development of electromagnetic models. The studies are extended to the case of high angular resolution, that's mean to the speckle pattern. We show that the analysis of the polarization state of the scattered field permits to complete this study and to identify signatures of the different polarization sources which are surfaces or bulks. An application will then be to annul each scattering source in order to select the characterized element.
The validity of the Ellipsometry of Angular Resolved Scattering technique introduced in a well known scatterometer has been demonstrated. The results were applied to the separation of surface and bulk effects in low-loss samples, because first-order scattering only depends on the origin of scattering, not on the topography or microstructure. The major point that we address is then the generalization of the separation technique (surface or bulk) to arbitrary heterogeneous samples with high level diffuse reflectance. The problem is strongly different since phase data from these samples depend on microstructure, not only on the physical origin of scattering.
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