Taper-etching method and method of manufacturing near-field light generator

A method of manufacturing a near-field light generator, the near-field light generator comprising a waveguide and a plasmon generator, wherein:

• the waveguide includes a core through which light propagates, and a cladding that surrounds the core;
• the core has a top surface;
• the cladding includes a cladding layer that has a groove located above the top surface of the core;
• the groove has two wall faces that intersect at a predetermined angle;
• and
• the plasmon generator has:
• two slopes opposed to the two wall faces;
• an edge part defined by the two slopes intersecting each other;
• and a near-field light generating part located at an end of the edge part and generating near-field light,
• the near-field light generator being configured so that the light propagating through the core is totally reflected at the top surface of the core to cause evanescent light to occur from the top surface of the core, and a surface plasmon is excited on the edge part through coupling with the evanescent light, the surface plasmon propagates along the edge part to the near-field light generating part, and the near-field light generating part generates near-field light based on the surface plasmon,
• the method comprising the steps of:
• forming the core;
• forming the cladding;
• and
• forming the plasmon generator, wherein:
• the step of forming the cladding includes the steps of:
• forming a layer to be etched, the layer to be etched being made of a dielectric material and having a top surface;
• forming an etching mask on the top surface of the layer to be etched, the etching mask having an opening;
• and
• taper-etching a portion of the layer to be etched, the portion being exposed from the opening, by reactive ion etching so that the groove is formed in the layer to be etched and the layer to be etched thereby becomes the cladding layer, wherein:
• the step of taper-etching employs an etching gas containing a first gas contributing to the etching of the layer to be etched and a second gas contributing to deposition of a sidewall protective film, and changes, during the step, a ratio of a flow rate of the second gas to a flow rate of the first gas so that the ratio increases;
• the layer to be etched is made of SiO2 or SiON;
• the etching mask contains elemental Al;
• and
• the second gas contains N2.