Characterization of $TiO_2$ thin films formed by plasma enhanced atomic layer deposition

Abstract

The growth of titanium dioxide ($TiO_2$) films has attracted a great deal of attention in electronic devices because of their highest dielectric constant in binary oxides. In this work, $TiO_2$ films deposited by plasma-enhanced atomic layer deposition (PEALD) using titanium isopropoxide (TTIP, $Ti(OCH(CH_3)_2)_4$) and oxygen radicals were studied. Even though, in conventional ALD, $H_2O$ or $H_2O_2$ was a oxygen precursor to deposit $TiO_2$, we suggested that oxygen could be used as oxygen precursor using PEALD below 300℃, where reactions between TTIP and oxygen did not happen. The film growth mechanism was investigated and film characteristics were analyzed by optical, structural, compositional and electrical properties. With the concept of PEALD, $TiO_2$ films were grown at process window of 150 - 300℃ and the pressure of 3 torr. In this temperature range, the growth rate increased with decreasing temperature and the fully saturated thickness per cycle was 0.67Å /cycle at 150℃. Also, the optimal plasma conditions were obtained with the plasma time, plasma power and Ar/$O_2$ ratio. The refractive index of was measured up to 2.58 at 950Å film grown at 275℃ in accord with the density of 4.09g/㎤ measured from RBS analysis, which are as high as bulk $TiO_2$. From Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RBS) analysis, titanium dioxide films by PEALD had oxygen-rich phase ($TiO_{2.23}$) and also there were carbon concentrations as low as about 1 ~ 2 at. %. The crystal structures of as-deposited films were amorphous structure in all temperature range while annealed films at 650℃ for 2min showed anatase peak at the θ = 25.44° corresponding to (101). The electrical properties of $TiO_2$ films were determined by I-V and C-V measurements. Leakage current of as-deposited films at 225℃ was 1.27E-6A/㎠ at 1MV/cm. After annealing process, the leakage current density of Ar annealed film was increased to 2.55E-6A/㎠ while that of $O_2$ an...