Semiconductor device having semiconductor optical waveguide and opposed insulator-filled trench and manufacturing method thereof

A manufacturing method of a semiconductor device, comprising the steps of:

• (a) preparing a first semiconductor substrate having a first insulating film formed on an upper surface thereof and a second insulating film formed on a lower surface thereof and a second semiconductor substrate having a third insulating film formed on an upper surface thereof;
• (b) forming a trench having a first depth from an upper surface of the first insulating film in the first insulating film and the first semiconductor substrate by sequentially processing the first insulating film and the first semiconductor substrate;
• (c) burying a fourth insulating film in the trench to form a cladding layer made of the fourth insulating film;
• (d) bonding the first semiconductor substrate and the second semiconductor substrate by bonding the first insulating film and the cladding layer to the third insulating film by heat treatment;
• (e) processing the second semiconductor substrate to a predetermined thickness to form a semiconductor layer made of the second semiconductor substrate;
• and
• (f) processing the semiconductor layer to form an optical waveguide made of the semiconductor layer in a region overlapping the cladding layer in a plan view,
• wherein a thickness of the third insulating film is 1 μm or less, and
• a distance from an interface between the optical waveguide and the third insulating film to a bottom surface of the trench is 2 μm or more.