SON device and manufacturing method thereof

The invention provides an SON device and a manufacturing method thereof. The manufacturing method comprises the following steps: providing a semiconductor substrate; forming a groove in the semiconductor substrate, wherein the groove is provided with a first side wall and a second side wall; a dielectric layer is formed, the dielectric layer covers the surface of the groove and extends to cover the surface of the semiconductor substrate, and the dielectric layer comprises a first dielectric layer and a second dielectric layer which are stacked; filling a decomposable material layer in the groove; etching back the decomposable material layer to remove a part of the decomposable material layer and a part of the dielectric layer covering the first side wall so as to expose a part of the first side wall; forming an epitaxial layer filling the groove from the exposed first side wall through an epitaxial growth process; removing the second dielectric layer through a wet etching process, and forming a gap on the sec