Your problem is likely not the size of the hole. The pressure of 4 Torr should
be adequate.

  There may be other problems, though
  (1) The resist may nto be cleared from the etch holes

  (2) The Si could have a significant native oxide that is slowing initiation of
the etch.  You might consider doing a BOE or BHF dip to minimize the native
oxide before etching.

  (3) If the *wafer* is at 75-95C this could slow the etch rate, since the etch
rate is partially governed by adsorption of XeF2 at the Si surface.  You might
try keeping the wafer at a lower temperature.


Bin Liu  wrote:
  Dear All,

I plan use XeF2 etch silicon. The XeF2 is designed to go through several
3*5um holes of photoresist and then etch away the silicon underneath. I
want the etched area to be 20um in radius. I heated up the XeF2 to
75C-95C during the etching process, the pressure during etching is
around 4 torr, I flush the XeF2 every 10 min, and got the sample sitting
in the gas for 40 min, but I still get very limited etching area through
the holes. I wonder if anyone have experience on XeF2 etching silicon,
can you give me some suggestion? the temperature? the pressure? or is it
because the holes are so small that limit the etching area?