Fig. 2(a) shows the effect of growth temperature on the GPC and nr of SnO2 thin films. With increasing growth temperatures from 150 and 350 °C, the GPC slightly increased from 0.05 to 0.072 nm/cycle, while the nr showed an almost constant value of 1.95. From a careful study on the growth kinetics of PEALD-SnO2 at 350 °C and the fact that the thermal decomposition temperature of SnCl4 is higher than 500 °C [2], the possibility of thermal decomposition of SnCl4 can be excluded from the origin of the increase in GPC. Therefore, it is plausible that the lower GPC at low growth temperatures is due to an incomplete reaction between chemisorbed SnCl4 and plasma at given temperatures, which is a similar effect of the low plasma power, as seen in Fig. 1(c). As shown in the inset images of Fig. 2(a), RBS spectrum indicated that Cl impurities was not exist in the films deposited at 150 and 350 °C. It is thought that PEALD-SnO2 thin films using SnCl4and O2 plasma can be deposited as impurity-free films through the clear ligand elimination reaction by oxygen radicals. Based on the simulation analysis of RBS, PEALD-SnO2 thin films using SnCl4 and O2 plasma exhibited an oxygen-rich stoichiometry, while the O/Sn atomic ratio of the films decreased from 2.23 to 2.04 when the deposition increased from 150 to 350 °C. A similar behavior (depending on the growth temperature) was in good agreement with previous studies by Choi et al. [8] and Heo et al. [2]. It was suggested that oxygen-rich SnO2 thin films resulted from unstable oxygen species such as hydroxyl groups, interstitial oxygen, or oxygen at grain boundaries at low growth temperatures. Furthermore, the oxidation of the substrate surface by exposure to the energetic O2 plasma at the initial growth stage could contribute to the oxygen abundance found in the RBS analysis. From the areal density of the film obtained by RBS, the volume density of the PEALD-SnO2 thin film was calculated as 5.95 g/cm3 and 6.72 g/cm3 at 150 and 350 °C, respectively, which was in accordance with the bulk density (6.95 g/cm3).