| 摘要 |
An SiO<SUB>2 </SUB>film is formed on a semiconductor layer stack, the SiO<SUB>2 </SUB>film having a thickness da and an etch rate Ra in buffered (BHF). A waveguide ridge with the SiO<SUB>2 </SUB>film thereon is formed using a resist pattern 76 . An SiN film is formed on top and both sides of the waveguide ridge, while leaving the resist pattern in place, the SiN film having a thickness db and an etch rate Rb in BHF, where 1<(db/Rb)/(da/Ra). Then the resist pattern and the overlying portion of the SiN film are removed by lift-off to form an opening in the SiN film. Wet etching for a predetermined period of time with BHF removes the SiO<SUB>2 </SUB>film from the waveguide ridge, while leaving the SiN film in place.
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