Dear all:
  I am bothered by two questions now. First, could heavily doped
Arsenic be formed as etch-stop layer, just as Boron,
in TMAH or KOH layer? The other is the etch selectivity
between heavily doped silicon with Arsenic and lightly doped
silicon with Boron. Any suggestion or reference will be appericiated
greatly.

Thanks in advance.
Sincerely,
Li Gang