An XPS Study of Silicon Oxynitride Rapid Thermally Grown in Nitric Oxide
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* Dept of Electrical Engineering, National University of Singapore, Singapore, [email protected] ** Central Characterization Laboratory, Institute of Materials Research and Engineering, Singapore *** Surface Science Lab, Dept of Physics, National University of Singapore, Singapore * R & D Dept, Chartered Semiconductor Manufacturing Limited, Singapore ***** Applied Materials South-East Asia Pte Ltd, Singapore
ABSTRACT
Earlier growth studies on the rapid thermal oxidation of silicon in NO (RTNO) were not sufficiently comprehensive and were limited by temperature measurement uncertainty and thermal non-uniformity across the wafer. Using a state-of-the-art rapid thermal processing (RTP) system, the RTNO growth characteristics at 100 and 760 Torr, from 900 to 1200°C and from 0 to 480 s were investigated. It was found that the initial growth rate anomalously decreasedwith temperature and pressure. These anomalies were correlated to the evolution of the XPS N Is spectrum of the RTNO film with oxidation time, temperature and pressure. INTRODUCTION
Earlier RTNO growth studies were limited in the process conditions employed, temperature measurement uncertainty, and thermal non-uniformity across the wafer [1,2]. Most of them only report that RTNO growth saturates rapidly to less than 40 A and have not looked in detail how it changes with process conditions, especially in the initial growth regime [3-5]. We therefore found incentives to do it again using a more extensive set of process conditions in a state-of-the-art RTP system [6]. EXPERIMENT
200 mm lightly B-doped CZ Si wafers were RCA cleaned immediately before they were processed in the RTP system in a single-step cycle. The RTP system employed in this study is the Applied Materials RTP XEplus Centura, which is equipped with W-halogen lamps and a concise and emissivity-independent temperature measurement and control system. The process chamber was purged with ultra-pure N2 before each wafer was processed. The oxidation conditions include two different pressures (100 and 760 Torr) as well as a wide range of oxidation temperature (900 to 1200 'C) and time (0 to 480 s). A gas flow rate of 5 slm and wafer rotation rate of 90 rpm was maintained throughout the cycle. Oxide thicknesses were obtained by well-calibrated ellipsometry (wavelength = 673.0 nm) and assuming a bulk Si0 2 refractive index of 1.46 on a 49-point mapping. Selected oxide thicknesses in the ultrathin regime were verified by high-resolution transmission electron microscopy measurements. High-resolution XPS spectra were collected using a step size of 0.10 eV and normal takeoff angle in the VG Scientific EscaLab 2201XL, which is equipped with a monochromatic Al / x-ray source (ho = 1486.6 eV). Peaks were charge referenced to the Si0 2 band in the Si 2p spectrum at 103.0 eV. The peaks were not charge referenced to the substrate Si 2p or adventitious C Is peak
171 Mat. Res. Soc. Symp. Proc. Vol. 592 © 2000 Materials Research Society
as the former varies with dopant concentration while the latter is af
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