To provide a substrate for an AT-cut quartz oscillator and a high performance elastic surface wave (SAW) element consisting of a single crystal thin film having easy handling and to provide its light CVD manufacturing method.

A β-SiC (011) buffer layer (a quartz thin film being a low temperature growth buffer layer) 102 and a quartz (011) 103 as a growth layer are subjected to heteroepitaxial crystal growth on a silicon (011) substrate 101, then an area 104 where a quartz epitaxial thin film exists while being exposed is formed by removing an unnecessary silicon by an anisotropic etching by using an SiO2film formed on the back surface of the silicon substrate as a mask to form a diaphragm structure.

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