Mariana Fraga - Relationships among growth mechanism, structure and morphology of PEALD TiO2 films: the influence of O2 plasma power, precursor chemistry and plasma exposure mode

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      W ChiappimG   E TestoniA   C O C DoriaR   S PessoaM   A FragaN   K A M Galvão,K   G GrigorovL   Vieira1,2 and H   S Maciel. NanotechnologyVolume   27Number   30.



    Titanium dioxide (TiO2)   thin films have generated considerable interest over recent   years, because they are functional materials suitable for a wide   range of applications. The efficient use of the outstanding   functional properties of these films relies strongly on their   basic characteristics, such as structure and morphology, which   are affected by deposition parameters. Here, we report on the   influence of plasma power and precursor chemistry on the growth   kinetics, structure and morphology of TiO2 thin   films grown on Si(100) by plasma-enhanced atomic layer deposition   (PEALD). For this, remote capacitively coupled 13.56 MHz oxygen   plasma was used to act as a co-reactant during the ALD process   using two different metal precursors: titanium tetrachloride   (TiCl4)   and titanium tetraisopropoxide (TTIP). Furthermore, we   investigate the effect of direct plasma exposure during the   co-reactant pulse on the aforementioned material properties. The   extensive characterization of TiO2 films   using Rutherford backscattering spectroscopy, ellipsometry, x-ray   diffraction (XRD), field-emission scanning electron microscopy,   and atomic force microscopy (AFM) have revealed how the   investigated process parameters affect their growth per cycle   (GPC), crystallization and morphology. The GPC tends to increase   with plasma power for both precursors, however, for the TTIP   precursor, it starts decreasing when the plasma power is greater   than 100 W. From XRD analysis, we found a good correlation   between film crystallinity and GPC behavior, mainly for the TTIP   process. The AFM images indicated the formation of films with   grain size higher than film thickness (grain size/film thickness   ratio ≈20) for both precursors, and plasma power analysis allows   us to infer that this phenomenon can be directly related to the   increase of the flux of energetic oxygen species on the   substrate/growing film surface. Finally, the effect of direct   plasma exposure on film structure and morphology was evidenced   showing that the grid removal causes a drastic reduction in the   grain size, particularly for TiO2 synthesized   using TiCl4.

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