Comparison of SiH4 and Si2H6 RTCVD kinetics using in-situ spectroscopic ellipsometry

A comparison of SiH4 and Si2H6 chemical vapor deposition kinetics was performed in a rapid thermal processing (RTP) system at temperatures between 600 and 800 degrees C and reactant gas pressures between 1 and 25 mTorr. Quantitative assessment of the nucleation parameters and the microstructures of the deposited polycrystalline Si (poly-Si) films on SiO2 have been determined using in situ real time single wavelength and spectroscopic ellipsometry. In addition to ellipsometry, atomic force microscopy and cross-sectional transmission electron microscopy were used ex situ to observe the nucleation stage and the microstructures of the poly-Si films. In the present study we compare the nucleation, poly-Si blm microstructure and surface roughness using SiH4 and Si2H6 in the RTP system and show that under the same processing conditions the saturation nuclei density (10(10) cm(-2)) for Si2H6 is about 6 times higher than that for SiH4 and the poly-Si films from Si2H6 are smoother and have better columnar structure than those from SiH4. A particularly important parameter for selective epitaxial depositions is the time for nuclei to form, i.e. the incubation time. An operational incubation time were determined from the real time ellipsometric measurements and confirmed by AFM. The incubation times for using SiH4, and Si2H6 are different, but they show similar activation energies of about E-inc = 1 eV in the 600-800 degrees C range. A formula of incubation time t(inc) was obtained and expressed as follows: t(inc) = C/P e(E?(inc)/kT) The physical meaning and comparison with the previous experimental results from other Labs are also discussed.