Comparison of SiH 4 and Si 2 H 6 RTCVD Kinetics Using in-situ Spectroscopic Ellipsometry
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t.~= -ekr inc P The physical meaning and comparison with the previous experimental results from other Labs are also discussed. I. INTRODUCTION Interest exists for the selective epitaxial growth (SEG) of silicon, because this process offers a number of advantages" 2 , such as a via hole filling method for planarization and a diffusion microsource for attaining accurate dopant profiles. The conventional approach in chemical vapor deposition (CVD) processes to obtain selective deposition is the use of dichlorosilane with H2 and HC13. However, the employment of ultrahigh vacuum chemical vapor deposition (UHV/CVD) systems restricts the use of chlorine-containing Si source compounds in favor of silane or disilane as the reactants with H2. The use of Si2H6 in Si selective epitaxy by CVD 4 is motivated by low process temperature and high growth rate (ten times higher than that of the Sill4 process5 ). The effectiveness of SEG is determined largely by the nucleation of Si on SiO 2. The key parameters that characterize the nucleation process such as the time for stable nuclei formation, the incubation time, and the nuclei saturation density are difficult to measure by 115 Mat. Res. Soc. Symp. Proc. Vol. 470 0 1997 Materials Research Society
electron microscope, and a technique that allows real time monitoring of these parameters is valuable for process development. The conventional in situ surface probes cannot be used in the highly reactive and high-temperature ambient of a CVD reactor. However, ellipsometry has been shown to be capable of making measurements of nucleation, with monolayer sensitivity and 6789 In the present study we compare the nucleation, quantification of microstructure'"' polycrystalline Si (poly-Si) film microstructure and surface roughness using Sill4 and Si 2H6 in a rapid thermal CVD system . In situ and real time ellipsometry as well as AFM and crosssectional transmission electron microscopy (XTEM) were used for this study. II. EXPERIMENTAL The experimental apparatus consists of a RTCVD system and an in-situ ellipsometer9 . The ellipsometer is a custom built rotating analyzer ellipsometer similar to the system described by 10 Aspnes . The ellipsometry measurements are made in an inverted configuration (i.e., measured from below the sample).. The in-situ spectroscopic ellipsometry (SE) measurements were made with photon energies between 2.5 and 5.0 eV and at room temperature after cooling the sample. The real time single wavelength ellipsometry (SWE) was carried out at 340 nm (3.65 eV), since this wavelength is relatively insensitive to temperature for Si The experiments were performed on SiO 2 (thermally oxidized in dry 02 to about 20 nm thickness) covered single crystal Si (c-Si) wafers (p-type, (100) oriented) under total pressures of 0.02-0.5 Torr and temperatures of 600-800 oC. The source gases used for the investigation were Sill4 and Si2H6 (5%, diluted with He). III. RESULTS AND DISCUSSION 1. Comparison of Poly-Si Film Microstructure and Roughn
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