Stopping An Etch In A Planar Layer After Etching A 3D Structure

A method of fabricating a semiconductor device, comprising:

• forming a plurality of gallium containing III-nitride nanowires extending through a silicon nitride masking layer on a support, wherein the support comprises a gallium containing III-nitride semiconductor surface under the silicon nitride masking layer;
• forming a patterned mask over a first portion of the plurality of nanowires, such that a second portion of the plurality of nanowires are exposed and are not located under the patterned mask;
• etching the second portion of the plurality of nanowires to remove the second portion of the plurality of nanowires;
• monitoring by optical emission spectroscopy an amount of gallium byproduct during the etching of the second portion of the plurality of nanowires;
• and
• stopping the etching on detecting that the silicon nitride masking layer is substantially removed and the gallium containing III-nitride semiconductor surface is exposed.