Mechanism of <110> preferential orientation in microcrystalline silicon growth and its influence on post-oxidation property

Mechanism of the <110> preferential orientation in microcrystalline silicon (μc-Si) associated with deposition radicals is investigated by comparison of degrees of crystalline orientation to the radical density estimated by solving simultaneous balancing equations as a function of a SiH4 flow rate under the constant flow rate of H2. The calculation result shows that a few percent of Si2H5 radical is involved in the deposition radicals as the second largest number of radicals, and that it increases as a SiH4 flow rate increases. Agreement of its increase with the increase of (220) orientation suggests that dimeric radicals concern with the crystalline growth in the <110> direction. Furthermore, dependence of post-oxidation properties on crystalline orientation controlled by ratio of SiH4/H2 is investigated. While the crystalline volume fraction of the samples are almost equivalent at around 0.7 ∼ 0.8 and the crystalline grain sizes are almost identical between the samples, the post-oxidation properties are much different between the samples and strongly depend on the crystalline orientation. Another influence of SiH4/H2 ratio on μc-Si film growth, presumably etching of a-Si phase at the grain boundaries, is inferred from the infrared absorption spectra of the Si-Hn stretching mode which suggest the change of a-Si passivation condition on the grain boundaries depending on the crystalline orientation.