Papers

AVS1996 Session TF-WeM: In-Situ and Ex-Situ Characterization I

Wednesday, October 16, 1996 8:20 AM in Room 107B

Wednesday Morning

Start	Invited?	Item
8:20 AM		TF-WeM-1 Generalized Ellipsometric Characterization of Cubic and Hexagonal Boron Nitride Thin Films Deposited by Magnetron Sputtering on [100]-Si M. Schubert, B. Rheinlaender (University of Leipzig, Germany); E. Franke (Institute for Surface Modification e.V, Germany); H. Neumann (Institute for Surface Modification e.V., Germany); J. Hahn, M. Roeder (Technical University of Chemnitz, Germany) Hexagonal and cubic boron nitride thin films have been investigated by ex-situ spectroscopic generalized ellipsometry (GE). The boron nitride thin films were deposited by d.c. and r.f. magnetron sputtering on [100]-Si substrates. GE has recently been developed for investigation of anisotropic layered structures. Our GE measurements reveal that an effective uniaxial anisotropy perpendicular to the sample surface exists within the hexagonal boron nitride layers. Depending on the growth conditions the macroscopic optical behavior varies from optically positive to optically negative. We explain the observed macroscopic dielectric function tensor in terms of an average inclination of the microscopic c-planes towards the sample normal. From a multi sample analysis we obtain the ordinary and extraordinary refractive indices of hexagonal, and the isotropic optical constants of cubic boron nitride. As well, for each hexagonal boron nitride sample we obtain the average inclination of the c-planes with respect to the sample normal. The optical constants are in good agreement with known bulk values. The axis inclinations are confirmed by transmission electron microscopy investigations.
8:40 AM		TF-WeM-2 A Five Layer Stack of Nitride, Oxide, and Amorphous Silicon on Glass, Analyzed with Spectroscopic Ellipsometry H. Tompkins, P. Williams (Motorola, Inc.) A stack of nitride, oxide, amorphous Si, oxide, nitride on a glass substrate was fabricated and subsequently analyzed with Spectroscopic Ellipsometry. The oxides and nitrides were deposited by PECVD and the amorphous Si was deposited with sputter deposition. The optical constants of these materials depend on deposition conditions and hence handbook values cannot be used directly. The optical constants of the amorphous Si layer are modeled as a combination of Lorentz oscillators. A further complication is that the amorphous Si is opaque over about half of the spectral range. Drawbacks of the straight-forward analysis method are discussed and an enhanced analysis method is described and the results presented. The enhanced method improves the uncertainty in the thickness determination of two of the layers by an order of magnitude.
9:00 AM		TF-WeM-3 Comparison of Ellipsometry Measurements of ZrO\sub 2\ Films Deposited on Fused Silica Substrates in a Round-Robin Experiment, Part 2 F. Urban, III, P. Ruzakowski Athey, J. Elman (Florida International University); G. Exarhos, J. Jellison (Pacific Northwest National Laboratory); C. Pickering (Defence Research Agency, United Kingdom); J. Woollam (University of Nebraska, Lincoln) The thickness and optical properties of thin films may be determined by ellipsometry measurements of the polarization state change in light reflecting from the film surface. The method is becoming more popular, in part because data can be acquired both in situ and ex situ, and are sensitive to film thickness changes on the order of monolayers. The last decade has seen a dramatic increase in the number of ellipsometers, commercial and specially designed, each somewhat different. The purpose of the round robin experiment carried out here was to compare a wide variety of methods on samples prepared as identically as possible. In Part 1 there was reasonable agreement but small differences between the film thicknesses and optical properties determined by each research group.[1] The work to be presented explores these differences in detail to discover the effect of the different measurement protocols, film modeling, mathematical formalism, and numerical solution methods that were used by each group. Samples were prepared by one group (Exarhos) by reactively sputtering from a zirconium target using an argon and oxygen atmosphere. Substrates of fused silica were coated on a rotating planetary for improved uniformity. Samples prepared under identical conditions were sent to the laboratories of the authors for measurement and analysis. [1] Submitted, Thin Solid Films, same authors as above
9:20 AM		TF-WeM-4 Thin Film Characterization by Spectroscopic Ellipsometry: Overcoming the Data Analysis Challenge B. Johs, J. Woollam (J.A. Woollam Co., Inc.) Accurate and timely characterization of thin film structures is a very important aspect of many research and industrial applications. As a non-destructive and non-invasive optical technique, Spectroscopic Ellipsometry (SE) offers powerful characterization capabilities for a wide range of thin film problems. With many commercial spectroscopic ellipsometer systems on the market, acquiring accurate SE data has become a fully automated and routine process. However, analyzing the SE data to extract the relevant thin film parameters is not always so straight forward. In all but the simplest of cases, e.g., bulk samples and ideal single films on a substrate, extracting information from the SE data requires a model dependent analysis procedure. The development of an appropriate model and SE data analysis strategy are critical for the quantitative characterization of any given class of thin film materials/structures. If the model is incorrect or too simplistic to adequately fit the experimentally measured SE data, the resulting analysis may not accurately represent the true physical nature of the thin film structure being characterized. On the other hand, if the model or sample structure is overly complex, there may not be enough information content in the SE data set to uniquely determine all of the desired thin film parameters. Techniques and strategies for overcoming these SE data analysis challenges are presented in this talk, using several real-world examples: determination of thin film ITO optical constants in the presence of compositional grading, characterization of anisotropic films and substrates, and the simultaneous determination of optical constants and layer thicknesses in multi-layer film structures. Recent successes in performing real-time analysis of insitu SE data to characterize the deposition and etching processes of dielectric and semiconductor materials will also be presented.
10:00 AM		TF-WeM-6 Analysis of Plasma-Enhanced CVD Diamond Film Growth Processes from CO/H\sub 2\ and CH\sub 4\/H\sub 2\ Mixtures using Real Time Spectroellipsometry J. Lee, B. Hong, R. Messier, R. Collins (Pennsylvania State University) The preparation parameter space within which diamond films can be grown by plasma-enhanced chemical vapor deposition (PECVD) is quite extensive. Gas mixtures containing C, H, and O atoms can be used, and substrate temperatures can be varied from 400 to 1000C. Real time probes that can provide growth rate and film properties for a succession of thin films deposited on a single substrate are very useful for scanning extensive regions of parameter space. We have applied real time spectroellipsometry in order to characterized the growth of diamond on nanocrystalline diamond films under a wide range of conditions, including variations of the gas mixture and substrate temperature. The focus of this report is a comparison of film growth from CO/H\sub 2\ and CH\sub 4\/H\sub 2\ mixtures. We have found that for the growth of diamond films from 400 to 800C, using a standard CH\sub 4\/H\sub 2\ gas flow rate ation of 0.01, the deposition rate increases with temperature in accordance with an 8 kcal/mol activation energy for precursor incorporation. Identical behavior is observed using a CO/H\sub 2\ gas flow ratio of 0.2, suggesting that the film precursor is the same hydrocarbon radical(s) in each case. As the CO/H\sub 2\ flow ratio is increased above 0.5, the temperature dependence of the growth rate changes remarkably. At a CO/H\sub 2\ ratio of ~10, the deposition rate becomes sharply peaked near 400C with a maximum rate that is ten times higher than that obtained from CH\sub 4\/H\sub 2\ at 400C o\C. This is an indication that the film precursors under these conditions are no longer hydrocarbons, but activated CO species. In this study, we will compare the quality of nanocrystalline diamond films prepared with CO/H\sub 2\ ratios as high as ~20 and at temperatures as low as 200C, with standard films prepared at 750C from CH\s ub 4\/H\sub 2\.
10:20 AM		TF-WeM-7 Optical Properties of a Mixed-Metal Oxide Film, Co\sub 3\(Cr,Fe)\sub 3-x\O\sub 4\, Deposited by Spray Pyrolysis P. Ruzakowski Athey (PPG Industries, Inc.); F. Urban (Florida International University); W. McGahan (Nanometrics, Inc.); M. Tabet (Florida International University) A mixed-metal oxide, Co\sub 3\(Cr,Fe)\sub 3-x\O\sub 4\, is a PPG Industries Inc. thin film product used to enhance the energy performance of a variety of float glass substrates used in buildings and homes. Thin films of Fe\sub 2\O\sub 3\, Cr\sub 2\O\sub 3\, Co\sub 3\O\sub 4\ and Co\sub 3\(Cr,Fe)\sub 3-x\O\sub 4\ were each deposited by hand spray pyrolysis of metal acetylacetonates on heated soda-lime silicate float glass. Optical constants of each single oxide film were determined from the combined analysis of variable angle of incidence spectroscopic ellipsometry and normal transmittance (T) measurements, 300-1700nm, while including the non-zero absorption of the substrate as a fitting parameter. The mixed-metal oxide film was optically modelled with an effective medium approximation layer consisting of Fe\sub 2\O\sub 3\, Cr\sub 2\O\sub 3\, and Co\sub 3\O\sub 4\. Best fits were obtained by varying both the film thickness and the optical constants of each oxide phase making up the mixed-metal oxide. Surface roughness was measured with atomic force microscopy and included in the optical model where necessary. The oxide phases were identified with thin film x-ray diffraction analysis. The ratio of the metals in the mixed-metal oxide film was determined with x-ray fluorescence. The non-zero absorption of the soda-lime silicate glass was fitted by an ensemble of four Gaussian oscillators over the entire measured spectral range. Simultaneous fits of ellipsometry and T data from coated samples were computed to obtain the film thickness, optical constants, and the amplitudes of the four Gaussian oscillators representing the substrate absorption. Spectra for the optical constants of each metal oxide and the mixed-metal oxide are presented and discussed.
10:40 AM		TF-WeM-8 Extended-range FTIR-ATR Si Surface Spectroscopy using a Novel Ge Prism with an Epitaxial Si Overlayer E. Rudkevich, J. Sullivan, S. Nayak, D. Savage, L. McCaughan, M. Lagally (University of Wisconsin, Madison) Fourier Transform Infrared Spectroscopy - Attenuated Total Reflection (FTIR- ATR) is used widely to determine the decomposition pathways of molecules on Si surfaces with the goal of understanding semiconductor manufacturing processes such as chemical vapor deposition (CVD) and wet-chemical cleaning. FTIR-ATR has high spectral resolution and high sensitivity to adsorbates with small oscillator strength, but has a limited spectral range (<7 um) on Si because of Si bulk lattice absorption. We show that its possible to extend this spectral range to ~12 um by using a Ge ATR prism with a thin (~1000 \Ao\) epitaxial graded Si overlayer. The epitaxial Si acts as a crystalline Si substrate. The extended spectral range allows us to probe, in addition to the Si-H and C- H\sub x\ stretch vibrations, the fingerprint region of organic molecules as well as Si-H bending and Si-O stretch vibrations. The graded Si epitaxial layer is deposited on a Ge substrate using a Rapid Thermal Ultra-High Vacuum - Chemical Vapor Deposition (RT UHV-CVD) reactor, after which the substrate is fashioned into an ATR prism. Aspects of the growth of the Si overlayer (roughness and structural effects related to the tensile stress in the film) are monitored in real time with in-situ Reflection High-Energy Electron Diffraction (RHEED). We discuss the optical properties of this prism and compare it to a standard Si prism. We demonstrate the utility of this method by comparing spectra of HF- treated Si(001), the in-situ decomposition of t-butyl silane on Si(001), and in-situ CVD SiGe film growth with ones taken with standard Si ATR prisms. We describe effects of surface homogeneity and strain on the IR spectra and discuss uses of this method for broader growth applications. *Research supported by NSF
11:00 AM		TF-WeM-9 In Situ Characterization of Thin Films by Differential Reflectance Spectroscopy: Nucleation and Growth of Silver Films on TiO\sub 2\(110) Surfaces D. Gagnot, J. Jupille (Laboratoire CNRS/Saint-Gobain, France); Y. Borensztein (Laboratoire d'Optique des Solides, France); P. Gadenne (Laboratoire d'Optique et de Magnetisme, France) The in-situ analysis of the formation of thin films is essential to the understanding of the kinetics of growth (effect of deposition rate, metastable layers,...). We have set up an apparatus to probe metal films in real time during deposition under ultra-high vacuum conditions, at 150 K < T < 1000 K, by means of Differential Reflectance Spectroscopy (DRS) (via the energy position of the plasma and Mie resonances). In the present work, we have studied silver deposits on TiO\sub 2\ (110) with and without surface oxygen vacancies, the amount of which being controlled through the area of the Ti\super 3+\ feature in the X-ray photoemission Ti 2p spectrum. On TiO\sub 2\(110), silver has the tendency to form three dimensional (3D) layers. However, on a clean vacancy-free titanium oxide surface at room temperature, silver at low coverage forms a 2D layer characterized by a high energy plasma resonance (> 4 eV). In the same experimental conditions, the presence of oxygen vacancies favour the formation of 3D adlayers and increases the number of nucleation sites. Finally, carbonaceous impurities lead to the formation of 3D silver films with almost spherical clusters (form factor close to 1). As the film thickens, these prototypical surfaces still behave quite differently. The oxygen vacancies favour the percolation of the silver layer while carbonaceous impurities prevent it. These results compare well with ex situ observations made by atomic force microscopy (F. Creuzet, D. Gagnot, and J. Jupille, unpublished results) and field emission scanning electron microscopy.