A method for manufacturing includes the steps of forming a BCB resin region on a semiconductor optical device; processing a surface of the BCB resin region with inductively coupled plasma produced with a high-frequency power supply for supplying ICP power and a high-frequency power supply for supplying bias power, thus forming a silicon oxide film on the surface of the BCB resin region and roughening the surface of the BCB resin region with projections and recesses; and forming an electrode pad on the surface of the BCB resin region in direct contact with the silicon oxide film. The surface roughness of the BCB resin region and the thickness of the silicon oxide film on the surface of the BCB resin region are controlled by adjusting the bias power and the ICP power.