Papers

ICMCTF2000 Session C5: Modeling and Measurement/Ellipsometry et.al

Wednesday, April 12, 2000 8:30 AM in Room Sunset

Wednesday Morning

Start	Invited?	Item
8:30 AM		C5-1 Invited - Missing - McGahan Unknown McGahan (Consultant)
9:10 AM		C5-3 Optical Properties of Amorphous Tantalum Oxide Thin Films Measured by IR-VIS-UV (0.03eV-8.5eV) Spectroscopic Ellipsometry* E. Franke, M. Schubert, C.L. Trimble, M.J. DeVries, J.A. Woollam (University of Nebraska) Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure and total gas pressure have been varied. The infrared (IR) optical properties of amorphous tantalum oxide are investigated for the first time by ellipsometry from 0.03eV to 1eV. We obtained the characteristic lattice absorption resonances. We further observe additional infrared absorption modes at the same spectral positions for each sample, which we tentatively assign to tantalum-hydrogen or tantalum-hydroxyl bonding vibrations. The experimental infrared ellipsometric data were analyzed using Lorentzian lineshapes for each absorption mode observed in the spectra. The thin films were further analyzed by glancing angle-of-incidence X-ray diffraction, atomic force microscopy (AFM), and variable angle-of-incidence spectroscopic ellipsometry in the UV-VIS (ultraviolet; visible) spectral region from E = 1 eV to E = 8.5 eV. The tantalum oxide optical properties were extracted from a multiple sample regression formalism. We consider thin film porosity, and therefore analyzed the experimental ellipsometric data in the UV/VIS spectral region by an effective medium approach. We obtain information on the tantalum oxide optical properties, a percentage void fraction and the film thickness. The "optical" percentage void fractions correspond to surface roughness measured by AFM, and depend on deposition parameters. * BMDO # DSAG60-98-C-0054, NASA Glenn Research Center grant # NAG3-2219, and NASA Epscor grant # NCC5-169
9:30 AM		C5-4 A New Combined Instrument with UV-visible and Far Infrared Spectroscopic Ellipsometry for Optical Thin Film Characterization B.P Boher, J.P.P. Piel, J.L.S. Stehle (SOPRA, France) Spectroscopic ellipsometry has long been recognized as a powerful technique to characterize thin films and multilayer structures. It is now routinely used for non-destructive on-line characterization of semiconductor process. SOPRA, leader in commercial spectroscopic ellipsometer for research and development, has decided recently to offer an instrument capable to cover the largest wavelength range available up to know (from deep UV 190nm to far infrared up to 18µm). The base is the up to date GESP instrument (Gonio Ellipso Spectro Photometer) which can work from 190nm to 2µm using a standard rotating polariser configuration with xenon lamp and Rochon polarisers. On the same setup, we have add another set of arms including globar source, Fourier transform interferometer, grid polarisers and MCT detector to be able to work from 1.44 to 18µm. All kinds of measurements (spectroscopic ellipsometry, photometry and scatterometry) and the analysis can be made from 190nm to 18µm with the same softwares. The proposed paper will present this new system with some examples of application concerning optical thin films.
9:50 AM		C5-5 Generalized Ellipsometry for Novel Optical Materials M. Schubert (University of Nebraska-Lincoln) Ellipsometry uses polarized light to determine optical properties and microstructure of materials, especially for thin films. Traditionally, this technique is restricted to isotropic materials only. Recently, a new global approach was developed from theory for anisotropic media, and implemented into numerous exciting experiments. This new field is called Generalized Ellipsometry. Owing to its unique capability to characterize optical and structural properties of general anisotropic, and hence complex sample systems, this technique enables new insights into physical phenomena of thin films, and provides precise structural and optical data of novel materials such as chiral liquid crystals for high-resolution displays, group III-V semiconductor compounds for LED and Laser applications, and magneto-optic layers for mass data storage devices. The concept and calculus of Generalized Ellipsometry is outlined. This calculus spans the symmetric and nonsymmetric dielectric, twisted symmetric dielectric, and symmetric and nonsymmetric magnetic materials. Applications of theory and experiment are discussed to demonstrate the ability of Generalized Ellipsometry for analysis of complex multilayered samples with inherent and arbitrarily oriented anisotropy.
10:30 AM		C5-7 Ellipsometry on Thin Layers of Biological Interest: Characterization and Applications H. Arwin (Linköping University, Sweden) The developments of instrumentation and methodology for optical characterization have advanced to a level allowing a detailed analysis of thin layers and complicated microstructures. The thickness resolution and in situ advantage of ellipsometry make this optical technique particularly suitable for studies of thin organic layers of biological interest. Early ellipsometric studies in this area mainly provided thickness quantification, often expressed in terms of surface mass. However, with state of the art methodology it is now possible to perform monolayer spectroscopy, e g of a protein layer at a solid/liquid interface, and also to resolve details in the kinetics of layer formation. Furthermore, complicated microstructures, like porous silicon layers, can be modeled with ellipsometry and protein adsorption can be monitored in such layers providing information about pore filling and penetration depths of protein molecules of different size and type. Quantification of adsorption and microstructural parameters of thin organic layers on planar surfaces and in porous layers are of large interest, especially in areas like biomaterials and surface-based biointeraction. Furthermore, by combining ellipsometric readout and biospecificity, possibilities to develop biosensor concepts are emerging. This leads to a technology transfer in form of instrumentation dedicated for sensor applications. In this report we review the use of ellipsometry in various forms for studies of organic layers with special emphasis on biologically related issues including in situ monitoring of protein adsorption on planar surfaces and in porous layers, protein monolayer spectroscopy and ellipsometric imaging for determination of thickness distributions. Included is also a discussion about recent developments of biosensor systems and possibilities for in situ monitoring of engineering of multilayer systems based on macromolecules.
11:10 AM		C5-9 Ellipsometric Investigation of the Si / SiO₂ Interface Formation for Application to Highly Reflective Dielectric Mirrors. B. Gallas, S. Fisson, A. Brunet-Bruneau, G. Vuye, J. Rivory (Laboratoire d'Optique des Solides, France) Silicon and silicon dioxide are widely used in opto-electronic applications either for detectors (microcrystalline or hydrogenated silicon for solar cells) or for reflectors. Si / SiO₂ multilayer stacks have been also proposed as reflectors to enhance the emission or the absorption in opto-electronic devices. Recently photonic crystals have also been proposed using the replication of interfaces during the growth and the high index difference between these materials in the near infrared range. For achieving efficient coatings, the abruptness of the interfaces is of importance. In particular inter-mixing and surface roughness could be detrimental to the quality of the interfaces. In this work we present a study of the Si / SiO₂ interface formation during the growth of Si on SiO₂ using in-situ ellipsometry measurements performed at one wavelength. Variable angle x-ray photoelectron spectroscopy (XPS) is also used to confirm the ellipsometric measurements. In-situ ellipsometry and XPS provide evidence for the formation of a SiO_x (02 and Si layers. The variation of x with depth is analysed from (cosΔ, tanΨ) trajectories and the results obtained allow to reproduce the spectroscopic ellipsometry spectra too. The effects on the growth of the temperature and of the surface roughness are investigated. The utilisation of a SiO₂ / Si multilayer stack for elaborating an omnidirectional reflector, angle-insensitive in the near infrared range, is also presented.
11:30 AM		C5-10 Characterization of Thin-film Amorphous Semiconductors Using Spectroscopic Ellipsometry G.E. Jellison, F.A. Modine, V.I. Merkulov, G. Eres, A.A. Puretzky, D.B. Geohegan, J.B. Caughman (Oak Ridge National Laboratory) Spectroscopic ellipsometry (SE) can now be used routinely to characterize amorphous thin films. Since SE measurements do not usually yield quantities of interest to the film grower by themselves, modeling and fitting are required to determine film thickness and optical functions. Recently, we have developed the Tauc-Lorentz model for the optical functions of thin films [Appl. Phys. Lett. 69, 371-373, 2137 (1996)], which has been very useful in interpreting SE results. The SE technique followed by data fitting with the Tauc-Lorentz model has been used to examine over one hundred amorphous carbon and amorphous silicon nitride films made by various film growth techniques. The results yield quantities such as film thicknesses, optical band gap, and complex refractive index, which then can often be directly related to other quantities, such as sp² to sp³ ratio and hardness for amorphous carbon films, and silicon-to-nitrogen ratio for amorphous silicon nitride films. The speed of the technique allows for a very quick, non-destructive evaluation of the thin-film quality.
11:50 AM		C5-11 Non-destructive Testing by means of Spectroscopic Ellipsometry: Fingerprint Spectra vs. Modelling U. Beck, M. MÄnn (Federal Institute for Materials Research and Testing (BAM), Germany) Spectroscopic ellipsometry is a powerful tool of non-destructive testing for the analysis of thin films, coatings and surfaces. It covers the optical responses of the electronic structure of materials from the VUV to the IR wavelength range in an almost non-destructive, non-contact, non-disturbing, and non-invasive way. For these reasons, spectroscopic ellipsometry is applicable to various application areas such as quality control (100 % testing), reference materials (certification), material engineering (material and layer design), statistical testing (repeatability, comparability), homogeneity testing (thickness uniformity) and special physical effects (anisotropy). In addition, from the UV to the NIR, neither the presence nor the absence of vacuum, plasma or air are affecting the measurement. In-situ (mainly single or multiple wavelength set-ups) and ex-situ applications (mainly spectroscopic set-ups) are present state of the art both for substrate and layer characterisation. Optical functions, i.e. refractive index and extinction coefficient, are material-related fingerprints of a given coating/substrate system. The determination of these physical quantities and of layer thickness as well requires model assumptions (layer design, effective medium approach). Despite the capability to check the quality of the model, e.g. by means of multiple angle measurements, the effort seems to be too high for many applications. A concept using ellipsometric quantities (raw data approach) or pseudo-optical functions (bulk approach at fixed angle of incidence) as fingerprints of a given system might be a satisfying solution to many industrial applications (quality control, statistical issues, yes or no decisions, within or without threshold limits, process repeatability, process comparability). Issues like accuracy, precision and uncertainties are discussed for specific applications on bulk materials, single layers, layer stacks and multilayers. In addition, the necessity of an optical inspection of the surface area under investigation is demonstrated for selected examples of analysis. As the fingerprint approach is also useful for the optimisation of the measurement conditions, it should be implemented in standard testing procedures.