Selective surface exposure, cleans and conditioning of the germanium film in a Ge photodetector

A method, comprising:

• forming a germanium layer on a semiconductor substrate;
• forming a nitride layer on the germanium layer;
• forming an oxide on the nitride layer;
• forming a photoresist layer on the oxide layer;
• patterning the photoresist layer to have an opening;
• performing a first etch to the oxide layer through the opening with a first chemistry;
• performing a second etch to the nitride layer through the opening with a second chemistry, the second etch being a timed dry etch that etches through about 75% to about 90% of the nitride layer with a second chemistry, to produce a protective nitride buffer over the germanium layer, the protective nitride buffer being about 10% to about 25% of an original thickness of the nitride layer;
• removing the photoresist layer with a third chemistry to which the germanium layer is sensitive, the protective nitride buffer protecting the underlying germanium layer from the third chemistry;
• performing a third etch to the protective nitride buffer, the third etch being a timed etch that etches through the approximate 10% to 25% of the nitride layer that was not previously etched in the second etch;
• and
• wet cleaning a surface of the germanium layer with a fourth chemistry that cleans the surface and conditions the atomic termini of the surface to be primarily either hydrophobic or hydrophilic.