Semiconductor device such as semiconductor laser device and manufacturing method therefor, and optical transmission module and optical disk unit employing the semiconductor laser device

A semiconductor device manufacturing method comprising:

• a first semiconductor layer forming step forming on a semiconductor substrate a first semiconductor layer that has an etching rate;
• a second semiconductor layer forming step forming on the first semiconductor layer a second semiconductor layer that has an etching rate slower than the etching rate of the first semiconductor layer;
• a third semiconductor layer forming step forming on the second semiconductor layer a third semiconductor layer that has an etching rate faster than the etching rate of the second semiconductor layer;
• an etching mask forming step forming an etching mask on the third semiconductor layer;
• an etching step etching, by using the etching mask and an etchant, the third semiconductor layer, the second semiconductor layer and the first semiconductor layer in a region outside the etching mask;
• and
• a thin film forming step forming a thin film such that the thin film continuously coats an upper surface and side surfaces of a semiconductor layer group that includes the third semiconductor layer, the second semiconductor layer and the first semiconductor layer remaining after the etching step.