Impact of Relative Humidity during Spin-Deposition of Metal Oxide Thin Films from Aqueous Solution Precursors

Relative humidity during the spin-processing of thin film solution precursors is often not controlled or measured, and its effect on film thickness is generally unappreciated. Herein, we report that the relative humidity during spin-processing has a marked impact on the film thickness of amorphous metal oxide (aluminum oxide and lanthanum zirconium oxide) and hafnium oxide-sulfate (HafSOx) thin films deposited from aqueous precursors. In the humidity range studied [20–95% relative humidity (RH)], film thicknesses varied by a factor of nearly 3, and this effect is independent of the metal precursor identity. Our data suggest that film thickness depends linearly on evaporation rate (100 – RH) for all systems studied, suggesting this effect is predominantly due to the unique characteristics of water as a solvent. In situ X-ray reflectivity studies of HafSOx films deposited under different humidities reveal that, while the thickness varies significantly with humidity, the density of the as-deposited films is ...