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Optical characterization of patterned thin films

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... Although microimaging ellipsometry is a well-established technique. [41][42][43] much fewer efforts have so far been made for large-area imaging of thin films. Our group has proposed a divergent light source configuration for large-area imaging. ...
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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 solution is to further reduce the complexity of the analysis by using more samples that are as homogeneous as possible on a millimetre-scale area. This could enable the definition of reference materials in the future that incorporate porosity as a referenced value similar to the already described references for layer thickness [43,44] and homogeneity/patterning [45]. ...
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The practical performance of surface coatings in applications like catalysis, water splitting or batteries depends critically on the coating materials’ porosity. Determining the porosity in a fast and non-destructive way is still an unsolved problem for industrial thin-films technology. As a contribution to calibrated, non-destructive, optical layer characterisation, we present a multi-method comparison study on porous TiO2 films deposited by sol-gel synthesis on Si wafers. The ellipsometric data were collected on a range of samples with different TiO2 layer thickness and different porosity values. These samples were produced by templated sol-gel synthesis resulting in layers with a well-defined pore size and pore density. The ellipsometry measurement data were analysed by means of a Bruggeman effective medium approximation (BEMA), with the aim to determine the mixture ratio of void and matrix material by a multi-sample analysis strategy. This analysis yielded porosities and layer thicknesses for all samples as well as the dielectric function for the matrix material. Following the idea of multi-method techniques in metrology, the data was referenced to imaging by electron microscopy (SEM) and to a new EPMA (electron probe microanalysis) porosity approach for thin film analysis. This work might lead to a better metrological understanding of optical porosimetry and also to better-qualified characterisation methods for nano-porous layer systems.
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The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(omega-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, R-q. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified.
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Two types of film thickness standards have been developed, manufactured and investigated - for X-ray reflectometry (XRR), X-ray fluorescence analysis (XRR), electron probe microanalysis (EMPA) on the one hand, and ellipsometry on the other. Metrological characterisation of both specific kinds of material measures and investigation results achieved are reported. The standards for XRR, XRF, EMPA consist of quarts substrate coated with Pt resp. a C-Ni-C-layer-system with a nominal metal layers thickness of 10 nm alternatively 50 nm. An established process for manufacture of X-ray mirrors was used for coating. XRR proved to be the dominant investigation method. Apart from film thickness characteristics like film thickness variances, interdiffusion between substrate and film have been analysed. In conclusion it can be estimated that the expanded measurement uncertainty of the film thickness for XRR applications is less than 0.5 nm. The standards for calibration of ellipsometer used for film thickness determination consist of an Si-substrate and an SiO2-film. They are provided with an additional topographic structure making a topographic film thickness determination (approximately) possible. The nominal values of film thicknesses are between 6 nm and 900 nm. Film thickness determinations were effected by XRR, Scanning Force Microscopy in combination with Transmission Electron Microscopy as well as various ellipsometrical techniques. The consistency of results found by different measurement techniques is discussed.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Optical constant spectra for silicon and thermally grown silicon dioxide have been simultaneously determined using variable angle of incidence spectroscopic ellipsometry from 0.75 to 6.5 eV. Spectroscopic ellipsometric data sets acquired at multiple angles of incidence from seven samples with oxide thicknesses from 2 to 350 nm were analyzed using a self-contained multi-sample technique to obtain Kramers–Kronig consistent optical constant spectra. The investigation used a systematic approach utilizing optical models of increasing complexity in order to investigate the need for fitting the thermal SiO2 optical constants and including an interface layer between the silicon and SiO2 in modeling the data. A detailed study was made of parameter correlation effects involving the optical constants used for the interface layer. The resulting thermal silicon dioxide optical constants were shown to be independent of the precise substrate model used, and were found to be approximately 0.4% higher in index than published values for bulk glasseous SiO2. The resulting silicon optical constants are comparable to previous ellipsometric measurements in the regions of overlap, and are in agreement with long wavelength prism measurements and transmission measurements near the band gap. © 1998 American Institute of Physics.
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Spectroscopic ellipsometry is a very powerful technique for optical characterization of thin-film and bulk materials, but the technique measures functions of complex reflection coefficients, which are usually not of interest per se. The interesting characteristics, such as film thickness, surface roughness thickness and optical functions can be determined only by modeling the near-surface region of the sample. However, the measured quantities are not equivalent to those determined from the modeling. Ellipsometry measurements determine elements of the sample Mueller matrix, but the usual result of modeling calculations are elements of the sample Jones matrix. Often this difference is academic, but if the sample depolarizes the light, it is not. Ellipsometry calculations also include methods for determining the optical functions of materials. Data for bulk materials are usually accurate for substrates, but are not appropriate for most thin films. Therefore, reasonable parameterizations are quite useful in performing spectroscopic ellipsometry data analysis. Recently, there has been an increased interest in anisotropic materials, both in thin-film and bulk form. A generalized procedure will be presented for calculating the elements of the Jones matrix for any number of layers, any one of which may or may not be uniaxial.
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SiO2 layers on Si are important for many applications, especially in the semiconductor industry. The thickness of the oxide layer can be determined from interferences in the X-ray reflectance, but these oscillations are very weak due to the low contrast between the optical constants of Si and SiO2 for the Cu Kα radiation (8048 eV) typically used. When monochromatized synchrotron radiation with an energy of 1841 eV slightly above the Si K edge is used, pronounced oscillations occur. Oxide layer thicknesses from a few nanometer up to 1 μm can be determined with low uncertainties.
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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.
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The problem of relating the specimen ψ and Δ to the instrument readings and component imperfections is solved by a general technique without any restriction on the nature of the imperfections. Thus, for the first time, small incoherent effects in the ellipsometer can be treated. The solution is explicit and is given in terms of the properties of the ideal ellipsometer and the Mueller imperfection matrices of the optical devices. After deriving the general solution, we consider a conventional ellipsometric arrangement. Arrays of coupling constants are introduced which clearly show the effect of imperfections on ψ and Δ. Also, we indicate in a schematic way the elements that remain effective after averaging over two and four zones. Component depolarization is discussed and the matrix elements contributing to it are found. Besides allowing all previous results to be obtained, some new conclusions of this analysis are: a small depolarization of the polarizer light output affects ψ (0.15° error in ψ for 1% depolarization) and this effect remains after two- and four-zone averaging. The effect of both coherent and incoherent p ↔ s cross scattering by the cell windows cancels if a two-zone average is taken. The same applies for the coherent and incoherent cross scattering by the specimen-surface roughness or by surface optical activity. For the compensator, cross scattering caused by birefringence and optical activity cancels only if a four-zone average is taken.
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No light is reflected from the air-water interface under Brewster angle incidence if p-polarized light is used. With constant angle of incidence, the formation of a monolayer on the water surface modifies the Brewster angle condition, and light reflection is observed. Reflectivity-area isotherms of arachidic acid monolayers on pure water and on aqueous solutions of different pH have been measured. Areas of different brightness due to different molecular density and/or refractive index in the monolayer have been recorded with a video system as micrographic pictures. This Brewster angle microscopy enables us also to detect monolayer inhomogeneities and the reversible formation of solid-phase domains upon compression of monolayers of DMPE.
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In the present work, we report low temperature (<285 °C) RF sputter deposition of silicon dioxide films for microelectronic and MEMS applications. The films were prepared by RF diode sputtering using a 3 inch diameter SiO2 target in argon atmosphere in the pressure range 5–20 mTorr and RF power from 100 to 300 W. The effect of deposition parameters (RF power and sputtering pressure) on various properties such as deposition rate, surface morphology, surface roughness, stress and etch rate of silicon dioxide films are investigated. The deposition parameters are optimized to obtain the films having low surface roughness and minimum stress. Due to the advantage of much lower thermal budget of the sputtering process compared to thermal oxidation, the application of RF-sputtered SiO2 films in IC fabrication is explored. Boron diffusion experiments are conducted using a sputtered SiO2 film as a masking layer. In order to investigate the application of RF-sputtered silicon dioxide films for MEMS, SiO2 microstructures such as bridges and cantilever beams were fabricated using bulk and surface micromachining processes. We also explore silicon wafer bonding using RF-sputtered silicon dioxide films as an intermediate layer.
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Imaging ellipsometry is presented as a technique for quantification and visualization of the lateral thickness distribution of thin (0–30 nm) transparent layers on solid substrates. The main advantage of imaging ellipsometry is that every point on a surface is measured at the same time with a high lateral resolution. The method is based on the use of combined null and off‐null ellipsometry at an incident angle close to the pseudo‐Brewster angle of a high index substrate such as silicon. In the present experimental setup, a xenon lamp, a collimator, and a wavelength‐selective filter provide an expanded collimated probe beam with a diameter of 25 mm. Other major components in the system are a polarizer, a compensator, and an analyzer. In this way, a 15×30 mm<sup>2</sup> image of a sample surface can be focused onto a charge‐coupled‐device video camera and transferred to a computer for further evaluation by image processing. Thickness measurements are performed for calibration purposes with ordinary null ellipsometry. The imaging ellipsometer has an accuracy of better than 0.5 nm at a lateral resolution of 5 μm in the present configuration, but improvements of at least a factor of 5 can be foreseen. Several aspects of the ellipsometric imaging system are illustrated in selected applications including continuous protein thickness distributions, stepped silicon dioxide thickness distributions, and visualization of protein patterning of surfaces. The latter can be used in a biosensor system as illustrated here by antigen–antibody binding studies. © 1996 American Institute of Physics.
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The modeling of spectroscopic ellipsometry data is reviewed, and is divided into three phases. The first phase involves the calculation of the Fresnel reflection coefficients for a given layer structure; it is shown that the Abelès formalism provides the most flexibility, and can be readily related to the Berreman formalism for calculations involving anisotropic layers. The second phase is to parameterize the optical functions of each individual layer; several models are reviewed, including effective media, the Lorentz oscillator and a recent parameterization of amorphous semiconductors. The final phase involves the fitting of the spectroscopic ellipsometry data to the model, where different figures of merit of the fitting function are discussed. A proper numerical analysis technique requires that the reduced ¢2 be used as the figure of merit, which will result in the proper weighting of data points, and in obtaining meaningful error limits and a measure of the goodness of fit.
Article
Spectroscopic ellipsometry is a very powerful technique for optical characterization of thin-film and bulk materials, but the technique measures functions of complex reflection coefficients, which are usually not of interest per se. The interesting characteristics, such as film thickness, surface roughness thickness and optical functions can be determined only by modeling the near-surface region of the sample Jones matrix. However, the measured quantities are not equivalent to those determined from the modeling. Ellipsometry measurements determine elements of the sample Mueller matrix, but the usual result of modeling calculations are elements of the sample. Often this difference is academic, but if the sample depolarizes the light, it is not. Ellipsometry calculations also include methods for determining the optical functions of materials. Data for bulk materials are usually accurate for substrates, but are not appropriate for most thin films. Therefore, reasonable parameterizations are quite useful in performing spectroscopic ellipsometry data analysis. Recently, there has been an increased interest in anisotropic materials, both in thin-film and bulk form. A generalized procedure will be presented for calculating the elements of the Jones matrix for any number of layers, any one of which may or may not be uniaxial.
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Silica-based integrated optical waveguide technology is reviewed. Low loss and manufacturable waveguides are made by chemical vapour, flame hydrolysis and electron beam deposition. Fibre to fibre insertion loss is as low as 0.3 dB for a 6 cm long waveguide. Bragg reflective add-drop filters are made with gratings formed by ultraviolet irradiation. The waveguide grating router has found important application as a multiplexer in dense wavelength multiplexed communications systems. Multiplexers with wide pass bands and stop bands are made with Fourier filters: these filters consist of a chain of alternating couplers and delaying arms. The good performance of waveguide grating routers and Fourier filters is due to the high degree of path delay and coupler control achievable by and processing in this technology
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SiO 2 xerogel thin film with a low dielectric constant was successfully prepared by a two-step acid-base catalyst procedure and successive surface modification with trimethylchlorosilane (TMCS). Only 15% porosity could be obtained without surface modification but with surface modification the porosity increased to 50%. These porosity values correspond to measured dielectric constants of 3.95 and 2.45, respectively. The low dielectric constant was revealed to depend mainly on the porous structure of xerogel thin film obtained with surface modification. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses were carried out to evaluate the effect of surface modification which induces the changes of surface coverage from --OC 2 H 5 and --OH to --CH 3 . Rutherford backscattering spectrometry analysis gave the porosity of SiO 2 xerogel thin film as 47.5%. The porosity estimation using refractive index obtained from Ellipsometry work was 43.2% and agrees well with RBS analysis. The network structure of SiO 2 xerogel was also evaluated with scanning electron microscopy and transmission electron microscopy. 1997 Elsevier Science S.A. Keywords: Silica xerogel film; Low dielectric constant; Porosity characteristics 1.
Numerical Recipes in C, The Art of Scientific Computing
  • W H Press
  • S A Teulolsky
  • W T Vetterling
  • B P Flannery
W.H. Press, S.A. Teulolsky, W.T. Vetterling, B.P. Flannery, Numerical Recipes in C, The Art of Scientific Computing, 2nd edition Cambridge University Press, New York, 1992.
  • V Bhatt
  • S Chandra
V. Bhatt, S. Chandra, J. Micromech. Microeng. 17 (2007) 1066.
  • C M Herzinger
  • B Johs
  • W A Mcgahan
  • J A Woollam
C.M. Herzinger, B. Johs, W.A. McGahan, J.A. Woollam, J. of App. Phys. 83 (1998) 3323.
  • G Jin
  • R Jansson
G. Jin, R. Jansson, H. Arwin, Rev. Sci. Instrum. 67 (1996) 2930.
  • D Hönig
  • D Möbius
D. Hönig, D. Möbius, J. Phys. Chem. 95 (1991) 4590.
  • J K Hong
  • H S Yang
  • M H Jo
  • H H Park
  • S Y Choi
J.K. Hong, H.S. Yang, M.H. Jo, H.H. Park, S.Y. Choi, Thin Solid Films 308-309 (1997) 495.
  • Q Zahn
  • J R Leger
Q. Zahn, J.R. Leger, Appl. Opt. 41 (2002) 4443.
  • G E Jellison Jr
G.E. Jellison Jr., Thin Solid Films 234 (1993) 416.
  • Y P Li
  • C H Henry
Y.P. Li, C.H. Henry, IEE Proc. Optoelectronics 143 (1996) 263.
  • G E Jellison
G.E. Jellison Jr., Thin Solid Films 313-314 (1998) 33.
  • R M Azzam
  • N M Bashara
R.M. Azzam, N.M. Bashara, J. Opt. Soc. Am. 61 (1971) 1380.