Control of orientation from random to (220) or (400) in polycrystalline silicon films

摘要

The control of grain orientation in polycrystalline silicon thin films on glass substrates by low-temperature techniques was investigated. Either (220) or (400) preferential grain orientation could be attained by control of source gas ratio over substrate temperatures between 250 °C and 360 °C. A remote type plasma chemical vapor deposition system was used with source gas mixtures of SiF_4, H_2 and Ar. The (220) preferential films were obtained with Ar/H_2SiF_4 gas flow rates of 60/15/30 sccm (respectively), while the (400) preferential oriented films were obtained at higher SiF_4/H_2 ratios (SiF_4/H_2 = 90/10 sccm). At the higher SiF_4/H_2 ratio during the crystal nucleation stage, either randomly oriented or (400) grains formed followed by the highly preferred deposition of (400) oriented crystallites. Raman scattering and ellipsometry spectra indicated that the (400) oriented films had a very smooth surface.