Role of HCl in Atomic Layer Deposition of TiO2 Thin Films from Titanium Tetrachloride and Water

Atomic layer deposition (ALD) of TiO2 thin film from TiCl4 and H2O has been intensively studied since the invention of ALD method to grow thin films via chemical adsorptions of two precursors.. However the role of HCl which is a gaseous byproduct in ALD chemistry for TiO2 growth is still intriguing in terms of the growth mechanism. In order to investigate the role of HCl in TiO2 ALD, HCl. pulse and its purging steps are inserted in a typical sequence of TiCl4 pulse-purge-H2O pulse-purge. When they are inserted after the first-half reaction (chemisorption of TiCl4), the grown thickness of TiO2 becomes thinner or thicker at lower or higher growth temperatures than 300 degrees C, respectively. However the insertion after the second-half reaction (chemisorption of H2O) results in severely reduced thicknesses in all growth temperatures. By using the result, we explain the growth mechanism and the role of HCl in TiO2 ALD.