David - At CWRU, we use about 0.5 slpm of N2 flow during idle. This
is introduced into the furnaces via a needle valve, eliminating the
need for an MFC. The idle flow runs continuously, but is shut off
during processing via a pneumatic valve.
As another suggestion, you may want to contact your furnace
manufacturer for their guidelines. By the way, we are set up to
run 4" wafers (in 6" diameter tubes).
As far as evaluating the "proper" flow, we periodically we monitor
mobile ion contamination through bias-temperature stress measurements;
we have not seen any problems with our current flow rate. Empirically
measuring oxide growth at low levels may be difficult.
Hope this feedback is helpful!
Acting Lab Manager, MFL
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