Semiconductor optical integrated device including a reduced thickness upper cladding layer in a ridge waveguide portion, and method of manufacturing the same

A method of manufacturing a semiconductor optical integrated device which includes a buried hetero structure waveguide portion and a ridge waveguide portion, the method comprising:

• a first step of layering at least a lower cladding layer and a waveguide core layer on a substrate in a region where the buried hetero structure waveguide portion is to be formed and a region where the ridge waveguide portion is to be formed;
• a second step of etching a semiconductor layer which includes the waveguide core layer in a mesa shape in the region where the buried hetero structure waveguide portion is to be formed;
• a third step of embedding a semiconductor cladding material near both sides of the waveguide core layer in the region where the buried hetero structure waveguide portion is to be formed;
• a fourth step of layering a semiconductor layer, which includes at least an upper cladding layer, in the region where the buried hetero structure waveguide portion is to be formed and the region where the ridge waveguide portion is to be formed;
• a fifth step of performing etching to remove a part of the upper cladding layer in the region where the ridge waveguide portion is to be formed;
• and
• a sixth step of removing both sides of the waveguide core layer in the regions where the ridge waveguide portion is to be formed and etching the semiconductor layer which includes at least the upper cladding layer in a mesa shape, in this order.