my last etch info

Jim McVittie mcvittie at snf.stanford.edu
Tue Jun 24 09:11:35 PDT 2003


Gigi,

Thanks for the info. I have no data on the effects of long pump downs other
than a reduction of water in the system. I guest F could come off the walls
during a long pump down. Over the years, I have seen several papers showing
the effects of F chemistries on subsequent Cl based etches. Generally, F
coming off the chamaber walls will suppress Cl etching for the first few
number of wafers run after the change over. The number of wafers or plasma
clean time needed to remove the F effect no doubt depends on the amount of F
run, the chamber and the Cl etch process details. Judy Hoyt at MIT has
recently been looking at this problem in their lab.
Before they changed to 6" wafers on their P5000, they ran both SF6 and Cl2/HBr
etch chemistries for Si etching. After the 6" upgrade for some reason they
could not run SF6 in the chamber for some time. They found that during the
period without SF6, they got much better poly Si etching with the Cl2/HBr. The
last time I talked to Judy, they were looking at banding SF6 from their poly
Si etch chamber. I think they should be able to live with both chemistries but
they have good results and no one want to do the testing. So far we have not
seen any reason to band SF6 or CF4 from any of our Si etch chambers. In fact,
we use SF6/Cl2 as a chamber clean on the Lam.

    Jim

Luigi Scaccabarozzi wrote:

> Hi all,
> I would like to share some info about my last etch (last sunday) that may
> help writing the new policy or other users to get consistent results.
> Last sunday I did first O2 cleaning (30 min) and then run my recipe
> (GIGI2, Ar:BCl3:Cl2) for 45 min on a dummy.
> Then I etched my samples (GaAs with Ni mask) for 5 min. each (all details
> are in the logbook).
> Though I'm not sure yet about the etch quality,I found exceptionally good
> etch rates (1.3 um / 5  min or 2600 A/min which is even higher  than what
> I expect <~ 2000 A/min) and   the interesting thing is that the last user
> before me was Carl (according  to history, logbook and last run recipe),
> etching with SF6. Even more  interesting is the fact that Carl's etch was
> run  24 hrs earlier and  nobody used the machine in between (and it has
> not been manually cleaned, up to my knowledge).
> Moreover, I remember Ali noticed that his best etch was after a weekend,
> when nobody has used the machine.
> Maybe this is a coincidence or maybe the fact that the machine is left in
> pumpdown for enough time after a supposed "dirty" etch (I mean with
> fluorine) contributes to the cleaning process (or simply that Carl's
> recipe is compatible with mine).
> I ask Jim, or others more expert than me, if this is possible and/or if it
> makes sense.
> Hope this will help.
> Gigi
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