Hi all,

          Has anyone encountered with the problem of formation of blisters
inside the PSG film (LPCVD ~1.5um thick) which is deposited on top of LPCVD SiO2
(~0.5um thick) which inturn is deposited on top of LPCVD nitride and/or
patterned LPCVD P-doped PolySi-1 (0.5um thick)...??

  P.S: These blisters start to appear only when the LPCVD P-doped PolySi-2 (~2um
thick) [which is deposited on top of the above mentioned patterned PSG layer],
is annealed @ ~1000 oC.
  Possibility of surface contamination is expected to be the least, since,
cleaning @ each stage of the above mentioned process is thoroughly performed as
per that of standard CMOS line. Also the pattern of blistering from Die to Die
across the whole wafer is very similar & consistant.


  Thanks and Regards
  mrutyu