Try the following process steps;

    PROCESS
   Pour fresh Phosphoric Acid in your own designated quartz beaker and cover
with your own designated lid to prevent evaporation.
   Heat solution to 155C.
   NOTE: Wafers should not have resist on them when going into nitride strip
bath.
   Use your own designated Teflon cassette for this etch to prevent
contamination.
   Dip wafers in your own designated beaker of DI water for 15 second.
   Immerse in 6:1 Buffered HF (in your own designated plastic or Teflon beaker)
for 30 seconds. This is to remove any oxide layer that is on the top of the
nitride.
   Overflow rinse (in your own designated beaker) for 5 minutes.
   Blow Dry.
   Inspect.
   Immerse the wafers in DI water for 15 seconds (in your own designated
beaker).
   Immerse the wafers in the hot Phosphoric (nitride strip) solution and replace
the lid to prevent evaporation which effects the etch rates. Note 800A of
standard nitride takes about 40 minutes to strip in fresh solution (you may want
to go 50 minutes to make sure it is all off.
   Overflow Rinse with DI water for 5 minutes.
   Blow Dry.
   Inspect to be sure all the nitride has been removed (i.e. measure oxide under
the nitride -- if it is less than or equal to what you had originally, the
nitride is off.


[email protected] wrote:
  I am interested in chemical etching of silicon nitride LPCVD deposited.
Actually, I'm using BHF, but it has a slow etch rate (10A/min). Is there
something faster?
Thanks
Andrea