Semiconductor optical waveguide device and method for manufacturing the same

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

• forming a stacked semiconductor layer on a substrate, the stacked semiconductor layer including a first III-V group compound semiconductor layer to be a cladding layer, a first semiconductor layer to be a first core layer, a second III-V group compound semiconductor, layer to be an intermediate layer, and a second semiconductor layer to be a second core layer;
• forming a first insulating layer on the stacked semiconductor layer;
• forming a first mask on the first insulating layer;
• forming a patterned insulating layer including a first thick-film portion, a first thin-film portion, and a first level difference separating the first thick-film portion from the first thin-film portion by etching the first insulating layer using the first mask;
• forming a second mask on the patterned insulating layer;
• forming a first insulating layer mask by etching the patterned insulating layer using the second mask, the first insulating layer mask including a second thick-film portion, a second thin-film portion, and a second level difference that are formed from the first thick-film portion, the first thin-film portion, and the first level difference of the patterned insulating layer, respectively;
• etching the first III-V group compound semiconductor layer using the first insulating layer mask to a middle of a thickness direction of the first III-V group compound semiconductor layer;
• forming a second insulating layer mask having a shape of the second thick-film portion of the first insulating layer mask by etching an entire surface of the first insulating layer mask until the second thin-film portion of the first insulating layer mask is completely removed;
• and
• forming the first core layer and a first semiconductor mesa including the cladding layer by etching a remainder of the first III-V group compound semiconductor layer and the first semiconductor layer using the second insulating layer mask,
• wherein the patterned insulating layer has a pair of first edges extending along a first axis, the pair of first edges of the patterned insulating layer being spaced apart from each other by a first width,
• the first insulating layer mask has a pair of second edges extending along the first axis, the pair of second edges of the first insulating layer mask being spaced apart from each other by a second width smaller than the first width, and
• the second width defines widths of the first core layer and the first semiconductor mesa.