ICMCTF2004 Session C4/F2: Nondestructive and In-Situ Characterization Techniques and Process Monitoring

Wednesday, April 21, 2004 1:30 PM in Room California

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	C4/F2-1 Advances in Multichannel Ellipsometric Techniques for Nondestructive and In-Situ Characterization of Thin Films R.W. Collins (The University of Toledo); I. An (The Univesity of Toledo); C. Chen (The University of Toledo); A.S. Ferlauto (The Universityof Toledo); J.A. Zapien (The University of Toledo) Several recent instrumentation advances over the last five years have enhanced the performance and capabilities of rotating-element multichannel ellipsometers for non-destructive, in situ analysis of thin films, surfaces, and interfaces. First, a single rotating MgF₂ compensator has been incorporated into a multichannel ellipsometer, leading to an instrument in the PSC_rA configuration (P: polarizer; S: sample; C_r: rotating compensator; A: analyzer). This instrument provides spectra in the unnormalized 4x1 Stokes vector of the light beam reflected from a sample surface in a minimum time of ~25 ms. Second, frequency-coupled dual-rotating compensators have been incorporated into a multichannel ellipsometer, yielding an instrument in the PC_1rSC_2rA configuration. This instrument provides spectra in the unnormalized 4x4 Mueller matrix of a sample in a minimum time of ~0.25 s. Third, the spectral range of the single rotating-polarizer and compensator ellipsometers (P_rSA and PSC_rA configurations) have been extended well into the ultraviolet by incorporation of a tandem Xe-D2 source arrangement. The resulting instrument provides ellipsometric spectra from 1.5 to 6.5 eV in fully parallel operation. The single rotating-compensator multichannel ellipsometer has been demonstrated in recent studies of the evolution of crystalline volume fraction in mixed-phase thin films prepared by plasma-enhanced chemical vapor deposition. In these studies, the thin films can be analyzed even when deposited on macroscopically structured substrates. The dual rotating-compensator multichannel ellipsometer has been applied to characterize the bulk complex dielectric functions of cubic crystalline solids as well as the surface-induced complex dielectric function anisotropy. This instrument has also been applied for high speed characterization of microstructure-induced optical anisotropy in thin films. Finally, applications of the uv-extended multichannel ellipsometers include studies of wide band gap thin film growth. In the case of boron nitride prepared by physical vapor deposition, for example, the extended uv spectral range provides the capability of discriminating between the cubic and hexagonal phases even in thin layers. Anticipated future applications of these new instruments will be discussed as well as future directions in the development of multichannel ellipsometry.
2:10 PM		C4/F2-3 In Situ Real-time Spectroscopic Ellipsometry Study of the Growth of Dense/porous Sin_X Multilayer Optical Thin Films A. Amassian, R. Vernhes, J.E. Klemberg-Sapieha, P. Desjardins, L. Martinu (Ecole Polytechnique de Montreal, Canada) We have recently demonstrated that multilayer and graded-index optical interference filters solely based on the control of film porosity can be fabricated through the modulation of ion bombardment energy during PECVD in a microwave/radio frequency discharge ¹. In the present work we investigate the growth mechanism of such dense/porous multilayer systems using in situ real-time spectroscopic ellipsometry (RTSE) combined with variable-angle spectroellipsometry (VASE), AFM, and SEM. When grown on c-Si, dense SiN_x films, obtained at high ion energy, E_i, exhibit bulk-like properties, with n ~ 2.0 (550 nm) and small surface roughness, R ~ 2 nm. Porous SiN_x films, deposited at low E_i, are porous and columnar, with n ~ 1.6 and R ~ 20 nm. Our results indicate that the optical properties, microstructure, and R of the dense films can be further tuned through the choice of the underlying film roughness. To demonstrate this effect, we focused on two limiting cases: (i) the growth of dense films directly on porous layers with high R, and (ii) the growth of dense films on surface-engineered porous layers with low R. When films are grown directly on a rough porous layer, RTSE data reveal surface porosity filling, before film thickness starts to increase. Films prepared under these conditions exhibit a lower average n (~1.8), an ascending n depth profile, and higher R (~10 nm) than the layers deposited under identical conditions on initially flat surfaces. On the contrary, ion bombardment of the initial porous film substantially decreases R. This provides a relatively flat surface layer on which the subsequently deposited dense film grown under intense ion bombardment develops homogeneous, bulk-like properties. Finally, surface-engineered dense/porous SiN_x multilayer stacks with improved optical performance have been fabricated. [1] R. Vernhes, O. Zabeida, J.E. Klemberg-Sapieha, and L. Martinu, Applied Optics, 2003, in press.
2:30 PM		C4/F2-4 Spectroscopic Ellipsometry Characterization of ITO Films Prepared by Reactive MF Dual Magnetron Sputtering: Effect of Substrate Temperature Mykola Vinnichenko (National Kyiv Taras Shevchenko University, Ukraine); A. Rogozin, N. Shevchenko, A. Kolitsch, U. Kreissig, W. Moeller (Forschungszentrum Rossendorf, Germany) The reactive middle frequency (MF) dual magnetron sputtering is a favorable process for industrial applications. Production of low resistivity (~10^-4 Ω cm) ITO films by this method requires their heat treatment. The ITO film formation and evolution at elevated substrate temperatures is not properly addressed because the phase diagram of this material is not known. Thus, in situ spectroscopic ellipsometry (SE) was applied to characterize the growth of ITO films at heated substrates (Ts=RT-510 C). The results of in situ and ex situ SE were compared with the film resistivity, stoichiometry (elastic recoil detection analysis) and structure (X-ray diffraction). The in situ SE indicates formation of the rough film with graded optical properties. This grading is stronger for the films deposited without substrate heating. The free electron parameters were determined from parameterization of the film optical constants in Drude-Lorentz approach. Their behavior with increasing Ts agrees with concomitant resistivity dependence, measured by the four point probe method. Thus, in situ SE monitoring of the free electron parameters provides a tool for real-time contactless characterization of the growing film resistivity. Quantitative characterization of the resistivity by SE requires further improvement of the optical model. The existence of the resistivity grading through the film thickness was indicated by this method for the growth without heating. At heated substrates this grading vanishes after deposition of ~50 nm layer and homogeneous film start growing. The films grown at the Ts=400 C have resistivity of 1.2 10^-4 Ω cm that is comparable with the best results achieved with ceramic targets. The SE data analysis demonstrated that improvement of the film resistivity with increasing Ts is mainly due to enhancement of the free electron mobility.It is accompanied by improvement of the film stoichiometry, changes of texture and crystallinity.
2:50 PM		C4/F2-5 Real-time Spectroscopic Ellipsometry Study during the Growth of Nanocrystalline and Nanolaminate Nitride Coatings S.M. Aouadi, M. Debessai, T. Maeruf, S. Stadler (Southern Illinois University Carbondale) Spectroscopic ellipsometry (SE) was employed to study the optical, electronic, and transport properties of various classes of nanocrystalline and nanolaminate nitride coatings grown by reactive unbalanced magnetron-sputtering. The investigated materials include TaZrN and NbZrN solid solutions, nc-ZrN/Ag and nc-ZrN/Ni nanocomposites, and Ta/ZrN and Ni/ZrN nanolaminates. Film properties were tailored by varying the energy and flux of bombarding ions and the substrate temperature. The following models were used to interpret the ellipsometric data: (a) effective medium theories describing the heterostructures in terms of their constituent materials and (b) a combined Drude-Lorentz model describing the optical response of the conduction and valence electrons. A correlation was found between the optical data and the chemical composition using the linear and Bruggeman effective medium approximations for the solid solution and the nanocomposite materials, respectively. The Drude-Lorentz model provided extensive information regarding the optical and electronic properties of the films (plasma frequency, electron mean free path, electrical resistivity, and band structure). In addition, the conduction electron mean free path was found to vary linearly with the number of nitrogen vacancies in the solid solution and with the grain size in the nanocomposite films. For the supelattice structures, the interdiffusion layers were monitored as a function of deposition conditions, which were then optimized to lead a quasi two-dimensional growth character. All SE findings were confirmed using X-Ray Diffraction, Transmission Electron Microscopy, and X-Ray Photoelectron Spectroscopy.
3:10 PM		C4/F2-6 In-Situ Optical Monitoring During the Growth of X-Ray Mirrors R Tomek, S. Stadler, S.M. Aouadi (Southern Illinois University Carbondale) Sputter-deposited Ni/C x-ray reflectors were investigated as a function of substrate bias and substrate temperature. Real time spectroscopic ellipsometry (RTSE) was used as a novel technique to: (1) understand the growth process of these structures; (2) provide a correlation between deposition parameters and interface quality; (3) calibrate deposition rates; and (4) control layer thicknesses. The end points in the ellipsometric data were used as reference points to indicate drifts in the growth rate, which were corrected for during deposition. The thicknesses measured using RTSE were calibrated using X-Ray Reflectivity, which provide thickness accuracy of <0.05 nm. In addition, Optical Emission Spectroscopy (OES) was utilized to monitor the intensity of the emission lines from the various species present in the sputter deposition plasma. OES was used as a real time tool to detect any drift in deposition rate and allow the operator to adjust the power output to the sputter guns. Real time process monitoring and control using both optical techniques improved the performance of these devices. The validity of the model architecture (period, thickness, roughness, interdiffusion) deduced from RTSE and OES were verified using glancing-angle x-ray reflectivity (GXR) measurements.
3:30 PM		C4/F2-7 Optical Constants of Thin Metal Films Determined by In-Situ Spectroscopic Ellipsometry and In-Situ Transmission Measurements N.J. Ianno (University of Nebraska-Lincoln); B. Johs (J.A. Woollam Co.) Ex-situ spectroscopic ellipsometry measurements of the optical constants of thin metal films (less than 10nm thick) are difficult to perform. This results from the fact that films of this thickness are discontinuous and rapidly oxidize upon exposure to air, yielding a complex mixture of voids, oxide and metal. In-situ ellipsometric measurements of the optical constants during film deposition would avoid this complication, however, in order to eliminate correlation effects and obtain accurate results, film transmission measurements are also needed. These could be obtained simultaneously with the ellipsometric data by utilizing a separate in-situ transmission system, or separately in a second set of in-situ transmission experiments. The first approach requires two measurement instruments attached to the deposition system. The second approach could utilize the ellipsometer as the transmission measurement instrument, requiring only a single instrument to perform both measurements. However, this method requires good reproducibility between deposition runs. We have utilized the second approach to determine the optical constants of molybdenum, titanium, Ti-V-Al alloy and graphite films 0 to 20 nm thick. We will show that a single set of optical constants can be used to predict the absolute film transmission, where this data has been experimentally verified.
3:50 PM	Invited	C4/F2-8 In-situ Characterization of Interfaces by High Energy Diffraction H. Reichert (Max-Planck-Institut für Metallforschung, Germany) Surfaces and interfaces are of fundamental interest in condensed matter physics and the availability of highly brilliant synchrotron radiation has boosted our understanding of the structure of surfaces and interfaces in the last decades. Most commonly, the structure of surfaces and interfaces is studied in surface scattering geometries (Grazing Angle Diffraction (GAD), Crystal Truncation Rod Diffraction (CTRD), and in specular and off-specular reflection geometry) at typical photon energies around 10keV. These techniques are not applicable in the case of deeply buried interfaces. Conventional x-ray scattering geometries are often unable to separate the scattering signals from structurally modified thin layers at an interface from the large background of bulk-like scattering signals. Especially for deeply buried interfaces, the strong absorption of the incoming and scattered photons within the capping material producing very weak scattering signals on top of a large background from the penetrated solid. We have recently developed a new diffraction technique using high energy microbeams in a high resolution setup which allows us to resolve most of these problems [1]. Examples of interfacial structures at deeply buried interfaces will be presented for a variety of materials like water, metals [2] and organic liquids. The examples demonstrate the applicability of our methods for the nondestructive and in-situ characterization of a broad range of interfacial structures. [1] H. Reichert et al., Physica B 336, 46 (2003). [2] H. Reichert et al., Nature 408, 839 (2000).
4:30 PM		C4/F2-10 Real-time Study of Crystalline Growth of Magnetron Sputter Deposition of Metal Coatings and Alloys S. Lee, J. Mueller, M. Cipollo (US Army Armament Research Development and Engineering Center, Benét Labs) An in-situ planer magnetron system, capable of real-time X-ray diffraction, was used to study effects of sputter parameter on crystalline nucleation and growth of tantalum and tungsten-titanium alloy coatings. Our investigation resulted in the following conclusions: 1) Substrate material plays an important role in tantalum phase formation. Under the same sputter gas pressure and plasma power, tantalum on glass resulted in growth of an amorphous interface layer, then a beta tantalum thin layer, followed by alpha tantalum growth. Tantalum on silicon wafer resulted in growth of predominately alpha phase tantalum. Tantalum on gun steel resulted in mixed alpha and beta Ta growth. 2) Sputter clean of substrate surface was very effective in improving coatings adhesion to substrate. Four sputter deposited tantalum on steel specimens showed improved adhesion after reverse sputter clean of the substrate. 3) Increased sputter gas pressure resulted in decrease in sputter rate, increase in grain size, and high (002) textured beta tantalum converting to more random beta tantalum. 4) Crystalline phase is not a sensitive function of sputter pressure in the gas pressure range (10-100mTorr) and plasma power (10-60 watts). 5) In separate experiments using a conventional planar magnetron system to study effect of substrate heating, substrate heating was shown to promote alpha over beta phase tantalum formation on gun steel substrate. 6) Alloy sputtering offers an alternative to metal coatings. Sputtered titanium-tungsten (10% Ti, 90% W) alloy target on steel substrate resulted in Ti-W alloy with similar stoichiometry as the target, but preferred W (110) orientation.
4:50 PM		C4/F2-11 Structure and Property Characterizations of Ta_0.1W_0.9O_x Thin Films Deposited by Pulsed Laser Ablation D. Yang, L. Xue (National Research Council Canada) Ta_0.1W_0.9O_x thin films were grown on Si (100) and ITO glasses at a substrate temperature range of 20 to 600°C using a KrF excimer laser operating at a wavelength of 248 nm and a repetition rate of 50 Hz. The laser beam was focused onto a 90-mm diameter Ta_0.1W_0.9O_2.95 target to induce its ablation in O₂ process gas with a pressure range of 1 to 40 mTorr. X-ray diffraction (XRD) results showed that Ta_0.1W_0.9O_x films deposited at a substrate temperature of 600°C were polycrystalline, while films with amorphous structure were obtained at lower substrate temperatures. Ta_0.1W_0.9O_x films deposited on both Si(100) and ITO glasses at high O₂ pressures preserved the chemical stochiometry of the Ta_0.1W_0.9O_2.95 target, and had the tetragonal crystal structure at substrate temperature of 600°C. Films deposited at lower O₂ pressures had oxygen deficiency with poorer crystallinity. Ta_0.1W_0.9O_x films deposited on ITO glasses appeared almost colorless at the O₂ pressure of 40 mTorr, while they had colors of light blue, blue and black respectively as the O₂ pressures decreasing from 20, 10 to 1 mTorr. Optical properties, such as index of refraction and extinction coefficient, of Ta_0.1 W_0.9O_2.95 films have also been determined by reflectance and transmittance measurements. Some potential applications of Ta_0.1W_0.9O_2.95 films in optical devices have also been evaluated.