Study of deposition temperature on high crystallinity nanocrystalline silicon thin films with in-situ hydrogen plasma-passivated grains

Publication date: 31 December 2015
Source:Thin Solid Films, Volume 597
Author(s): Czang-Ho Lee, William S. Wong, Andrei Sazonov, Arokia Nathan
This paper studies the effect of deposition temperature on the growth of nanocrystalline silicon (nc-Si) films deposited by 13.56MHz plasma enhanced chemical vapor deposition (PECVD) with in-situ hydrogen (H) passivation. A high crystalline volume fraction (XC) of 80% was found in the ~100nm nc-Si film deposited at 260°C with 99% H2 diluted SiH4 at intermediate RF power between the power-limited and precursor-limited regimes. Based on these optimized deposition conditions, 300–400nm nc-Si films deposited at 75–260°C also showed a high XC of 82–85%, an intrinsic-like dark-conductivity (σdark) of ~10⁻⁶ S/cm, and even a low mean oxygen content (CO) of 10¹⁷–10¹⁸ at./cm³. Although material properties were similar, deposition temperature appeared to change the qualitative structure of the nanocrystalline grains. The preferred grain orientation changed from 〈111〉 to 〈220〉 as the deposition temperature was increased from 75 to 260°C due to enhanced surface diffusion of deposition precursors. This reflected in more compact and lateral columnar growth of nc-Si films with increasing deposition temperature. We successfully demonstrated high field-effect hole and electron mobilities of 33.8 and 225cm²/Vs, respectively, in top-gate thin-film transistors (TFTs) employing the ~100nm nc-Si channel layer deposited at 260°C.