Room temperature plasma enhanced atomic layer deposition for TiO2 and WO3 films

Abstract

This paper presents a study on plasma enhanced atomic layer deposition (ALD) of TiO2 and WO3 films on silicon substrates. At low temperatures, ALD processes, which are not feasible at high temperatures, could be possible. For example, temperatures at 180 °C and above allow no WO3 ALD process with WF6 as a precursor because etching processes hinder film growth. Further low temperature deposition techniques are needed to coat temperature sensitive materials. For the deposition, WF6 and TiCl4 are used as metal precursors and O2 and H2O as oxygen sources. The depositions were accomplished in the temperature range of 30 °C up to 180 °C for both metal oxides. Spectroscopic ellipsometry, x-ray reflection, and grazing incidence diffraction were used to investigate the deposited ALD thin films. Film growth, density, crystallinity, and roughness are discussed as functions of temperature after ensuring the ALD requirement of self-saturating adsorption. Growth rates and measured material properties are in good agreement with literature data.