Role of ultra thin SiOx layer on epitaxial YSZ/SiOx/Si thin film

The role of an ultra thin SiOx layer for epitaxial growth of a YSZ (Y2O3 stabilized ZrO2) thin film on a (001)Si substrate through the SiOx layer was investigated by high resolution transmission electron microscope (HRTEM), in-situ heating transmission electron microscope and nano-beam diffraction (NBD) methods. It is found that a trace of epitaxial crystallinity remains in an ultra thin SiOx layer within 2 nm from SiOx/Si interface. According to this result, a YSZ layer could epitaxially grow only on an ultra thin 1-2 nm SiOx layer. It is also found that an ultra thin SiOx layer has another effect to relax the crystallization strain at a YSZ/Si interface. These results indicate that an ultra thin SiOx layer plays two important roles: (a) an ultra thin SiOx layer formed just above the Si surface serves as a medium for the epitaxial growth of a YSZ layer, and (b) even in an ultra thin SiOx is able to relax the crystallization strain of YSZ layer at YSZ/Si interface. These are the critical points of the epitaxial growth of YSZ/SiOx/(001)Si thin film together with a role of an oxygen source reported previously.