An Experimental and TheoreticalStudy of the Impact of the PrecursorPulse Time on the Growth Per Cycleand Crystallinity Quality of TiO2 ThinFilms Grown by ALD and PEALDTechnique

摘要

In this paper, theoretical and experimental approaches were used to evaluate the impactof the precursor’s pulse time on the growth per cycle and the crystallinity quality ofatomic layer deposited TiO2 thin films on Si(100) and FTO substrates. We employ ageneral model that can be applied to both metal and oxidant precursors, based onthe Maxwell-Boltzmann velocity distribution from which the molecular flux of gasesthat collide with the substrate is deduced to adjust the experimental characteristics ofgrowth per cycle vs. pulse time. This model allowed us to adjust the growth per cycleof TiO2 films produced by thermal atomic layer deposition and by plasma-enhancedatomic layer deposition under different deposition parameters and substrates. Theinfluence of growth per cycle on the chemical and structural properties of TiO2 thinfilms was evaluated by Rutherford backscattering spectroscopy, grazing incidence xray diffraction, and ellipsometry techniques. In thermal mode, using H2O as an oxidantprecursor, the stoichiometry of TiOx films has an x value of 1.98 from the growth percycle saturated regardless of the metal precursor or substrate used. Using O2 plasma,a super-stoichiometric film with x values from 2.02 to 2.30 was obtained. In thermalmode, the growth per cycle saturated and film thickness are, on average, 40% higherfor TiCl4 compared to TTIP precursor. Using O2 plasma, the growth per cycle saturatedis approximately twice as high as the thermal mode using the TTIP precursor. For bothatomic layer deposition modes, the degree of crystallinity showed values of 50–80% forTiCl4 in the temperature range of 250–350?C. For TTIP, it was below 40% in thermalmode and between 80 and 95% in plasma mode (250?C). It was observed that thereaction rate, the diffusion coefficient, and the molecular flux are inversely proportionalto the temperature. These results provide evidence that the crystallinity and epitaxialquality of the TiO2 film are higher for TTIP using O2 plasma. However, we verified that there was better stability of the parameters analyzed for TiCl4 in the two atomic layerdeposition modes.