Hello
We are having a problem with our LPCVD Nitride process;
We have an Advanced Scientific Materials   MICON III System.
Initially the problem showed up as:  Our film thickness was fairly even on
the first wafer, but every other wafer was 50% of intended thickness and
non-uniform
We have re-tested our process after sequentially doing the following:
=  Changed/repaired MFC for DiChlorosilane. and changed out tank.
=  Leak checked system - replaced bellows in valve - re-leak tested.
=  Changed the process to increase the silane flow from 300-550sccm which
has improved our          uniformity, but now we need a sacrificial wafer up
front  and a second wafer after the brace in the center of the boat.  We
have the same results with 3" & 4" wafers.

This has been an on-going dilemma for us for several weeks,  there have been
other changes / and instrument checks during that time.