Effect of ozone concentration on atomic layer deposited tin oxide

Tin dioxide (SnO2) thin films were deposited by atomic layer deposition (ALD) using tetrakis(dimethylamino)tin {[(CH3)2N]4Sn} and various concentrations of ozone (O3) at 200 °C. In order to characterize SnO2 thin films, the growth rate, thin film crystallinity, surface roughness, chemical bonding state, and electrical and optical properties were investigated. The growth rate of SnO2 increased slightly when the O3 concentration was increased. However, the growth rate was almost saturated above 300 g/m3 concentration of O3. Also, the x-ray diffraction patterns of SnO2 thin films become sharper when the O3 concentration increased. Specifically, the (101) and (211) peaks of SnO2 improved. In addition, the defects of the SnO2 thin films such as oxygen vacancy and hydroxyl group are related to the O3 concentration that was observed via x-ray photoelectron spectroscopy. As the O3 concentration is higher than 300 g/m3, the electrical Hall resistivity and mobility saturated 3.6 × 10−3 Ω cm and 9.58 cm2/V s, respectively. However, the carrier concentration slightly decreased to 3.22 × 1020 cm−3. It is assumed that the oxygen vacancies were filled with a high O3 concentration at ALD reaction. The optical bandgaps were larger than 3.5 eV, and the transmittance of all SnO2 thin films exceeded 90%. The O3 concentration below 200 g/m3 in the ALD process of SnO2 thin films is considered to be one of the factors that can affect the crystallinity, chemical bonding, and electrical properties.