Low temperature SiO_x thin film deposited by plasma enhanced atomic layer deposition for thin film encapsulation applications

Silicon oxide (SiO_x) films were synthesized by plasma enhanced atomic layer deposition (PEALD) using di-isopropylaminosilane [SiH₃N(C₃H₇)₂] as the precursor and an oxygen plasma as the reactant. The layers were characterized with respect to different growth temperatures between 60 and 150 °C. The film density and surface roughness values measured by x-ray reflectometry and atomic force microscopy all approached those of thermally grown SiO_x. Also, reasonably high breakdown voltages were observed at all deposition temperatures. An interesting phenomenon involves the fact that the SiO_x layer deposited at 60 °C is most effective as a moisture barrier, as it exhibits the lowest water vapor transmission rate. X-ray photoelectron spectroscopy analyses indicate that the silicon monoxide bonding characteristic becomes more pronounced as the growth temperature decreases. It is conjectured that such a difference in the bonding state renders the surface of the low temperature SiO_x films rather hydrophobic, which suppresses the penetration of moisture. The results indicate that low temperature PEALD SiO_x films may be suitable for thin film encapsulation applications in mechanical flexible platforms.