Papers

ICMCTF2002 Session C6-1: Optical Spectroscopy Including Ellipsometry: Modeling, Measurement and Process Control

Thursday, April 25, 2002 3:50 PM in Room Sunset

Thursday Afternoon

Start	Invited?	Item
3:50 PM		C6-1-8 Applications of uv-extended Real Time Spectroscopic Ellipsometry to Determine Phase Evolution of Cubic Boron Nitride Films Under Dynamic Substrate Bias Step-down Deposition Conditions. J.A. Zapien, R.W. Collins, R. Messier (The Pennsylvania State University) We have developed a uv-extended rotating-polarizer multichannel ellipsometer (uv-RTSE) having a photon energy range from 1.5 to 6.5 eV, a minimum acquisition time of 24.5 ms for full-spectra in (ψ, Δ), and sub-monolayer sensitivity at this high speed. As a result of its uv-extended spectral range, the new multichannel ellipsometer is ideal for studying the deposition of wide band gap thin films in real time, including diamond, cubic boron nitride (cBN), and silicon oxynitrides (a-SiO_xN_y), among many others. Here, we report the application of the uv-RTSE in studies of the growth and layered structure of cBN films deposited on c-Si using pulsed dc sputtering of a B₄C target with rf substrate bias. Based on the optical response in the uv spectral region (4.5 to 6.5 eV), it has been possible to characterize the phase evolution of the BN films using a three-layer model with constrained thickness evolution including: (i) an initial hBN layer; (ii) a hBN+cBN mixed-phase interface layer; and (iii) a cBN layer. The detailed layer evolution was obtained as a function of the substrate bias (V_avg) used to grow the BN films under steady-state conditions. The results of such analyses have been found to be in good agreement with ex-situ Fourier transform infrared spectroscopy (FTIR) performed at the end of the deposition. The effect of the deposition conditions on the phase evolution of films deposited under steady state conditions will be presented, as well as our results on the effect of low hydrogen addition (< 0.02 %) during BN deposition under dynamic deposition conditions (step-wise decrease in substrate bias). The stringent requirements of this application example demonstrate clearly the capabilities of uv-RTSE as an effective tool for real time characterization of wide band gap thin film growth.
4:10 PM		C6-1-9 Phase Modulated Spectroscopic Ellipsometry of Multilayer Dielectric Coatings D. Bhattacharyya, N.K. Sahoo, S. Thakur, N.C. Das (Bhabha Atomic Research Centre, India) Ex-situ analysis of multilayer structures is a difficult task due to the presence of a large number of interdependent parameters and Spectroscopic Ellipsometry is a very important tool in this respect, where important information regarding the thickness and optical constants of the layers can be derived quite accurately by fitting the experimental results with suitably modelled theoretical spectra. In the present work an algorithm to characterise e-beam evaporated TiO₂/ SiO₂ based multilayer optical coatings with large number of layers, by Phase Modulated Spectroscopic Ellipsometry, using a discrete spectral zone fitting approach has been demonstrated in the wavelength range of 280-1200 nm. In this technique, the ellipsometric spectra (ψ and δ versus wavelength) were fitted separately in three different wavelength regimes and efforts have been given to find out the lack of periodicity (if any) present in the structure due to the variation in thickness and/or refractive index values of individual layers. It has been assumed that these variations are confined to TiO₂ layers only since properties of TiO₂ are known to vary widely depending on deposition parameters. The refractive indices of SiO₂ layers have been taken from the reference data since it is a relatively well- behaved material. The ellipsometric spectra is fitted first in the wavelength regime of 700-1200 nm and the sample structure was determined. TiO₂ and SiO₂ layers have been assumed to be transparent in this wavelength regime and the dispersion of refractive index with wavelength has been neglected. The data were then fitted in the wavelength regime of 280-340 nm to find out the dispersion relation for the optical constants of TiO₂. Finally the fitting has been done in the wavelength range of 340-700 nm and the true dispersion of refractive index of TiO₂ along with the best fit sample structure have been obtained. The above approach has been successfully used in characterisation of a 23-layer multilayer high reflecting mirror and a 27-layer multilayer beam combiner.
4:30 PM		C6-1-10 Spectroscopic Ellipsometry Study on the Structure of Ta₂O₅/SiO_xNy/Si Gate Dielectric Stacks Yi-Sheng Lai, J.S. Chen (National Cheng Kung University, Taiwan, ROC) Amorphous tantalum oxide (Ta₂O₅) films are deposited on Si substrate for application as the gate dielectric in metal-oxide-semiconductor field-effect transistors (MOSFETs). Prior to Ta₂O₅ deposition, the Si substrate has been nitrided in an N₂O+ NH₃ plasma at 450°C to form a passive silicon oxynitride (SiO_xN_y) layer. In this work, spectroscopic ellipsometry is used to determine the complex refractive index, the complex dielectric function and the thickness of Ta₂O₅/SiO_xN_y stacks. To solve the ingredients of the dielectric layer, Bruggeman effective medium approach (EMA) model is applied to each layer of the stacks for the ellipsometry data. We have found that the EMA model could explain the composition of the two mixed phases (SiO₂ and Si₃N₄) in the SiO_xN_y layer as well as the porosity ratio in the Ta₂O₅ layer. In addition, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used as complementary methods to verify the film composition and thickness. The correlation between the process conditions and the nitrogen-dependent of the refractive index of the SiO_xN_y layer, as well as the porosity-induced refractive index lowering of the Ta₂O₅ layer will be discussed.
4:50 PM		C6-1-11 Tracking Ellipsometer of 0.1A Sensitivity Developed for In-situ Monitoring of Soft X-ray Multilayer Fabrication Y. Hotta, M. Sato, M. Yamamoto (IMRAM, Tohoku University, JAPAN) For the purpose of in-situ monitoring of soft X-ray multilayer fabrication, a tracking ellipsometer with a He-Ne laser source has been developed utilizing two phase faraday cell modulation of polarizer and analyzer azimuthal angles for tracking of the null(crossed Nicol) position. The ellipsometer has been successfully applied to monitor 70A period Mo/Si multilayer fabrication with an extremely high sensitivity of better than 0.1A, which reveals growth mode consisting of Mo-island growth, silicide formation at the Mo/Si and Si/Mo interfaces. The advantage of the ellipsometer will be discussed with emphasis on the ellipsometric deposition mass measurement for accurate deposition rate monitoring. The accuracy of 0.1deg achievable by the single zone measurement with systematic error elimination will also be discussed.