METHOD FOR MANUFACTURING MACH-ZEHNDER MODULATOR, METHOD FOR MANUFACTURING OPTICAL WAVEGUIDE, AND INSULATION-SEPARATED OPTICAL WAVEGUIDE

摘要

PROBLEM TO BE SOLVED: To provide a method for manufacturing a Mach-Zehnder modulator, by which a stepped portion on a side face of an optical waveguide can be decreased.SOLUTION: An insulation film mask 41 has an opening 41b corresponding to an opening 39b of a resist mask 39a. The insulation film mask 41 covers side faces and upper faces of a first portion and a second portion of a waveguide mesa 33 as well as covers side faces of a third portion of the waveguide mesa 33. A second clad layer of the semiconductor waveguide mesa 33 is etched by using the insulation film mask 41 to expose an upper portion of a core layer. In an embodiment of the present invention, the semiconductor waveguide mesa 33 is etched by using SOG (spin on glass) and SiON as a mask until the upper portion of the core layer is exposed. In this process, since the insulation film 35 has no opening other than a portion corresponding to a waveguide top, a first clad layer or an element separation mesa area located below the core layer of the waveguide mesa 33 cannot be etched.