BOX-shaped silicon nitride waveguide and preparation method thereof

The invention discloses a BOX-shaped silicon nitride waveguide and a preparation method thereof, and belongs to the technical field of optical materials, and the method comprises the steps: sequentially forming a first coating layer, a first sacrificial layer and a second sacrificial layer on a semiconductor substrate; etching the first sacrificial layer and the second sacrificial layer, and removing the second sacrificial layer to form a strip-shaped groove; growing a silicon nitride material, enabling one part of the silicon nitride material to grow in the strip-shaped groove, enabling one part of the silicon nitride material to cover the first sacrificial layer, and flattening the surface to form a BOX silicon nitride groove; growing a second coating layer, filling the BOX silicon nitride groove with a part of the second coating layer, covering the first sacrificial layer with a part of the second coating layer, and flattening the surface to form a smooth surface; growing a siliconnitride material and cove