LTO Status

Mary Tang mtang at snf.stanford.edu
Wed Sep 5 14:24:17 PDT 2001


Hello Tylan users --

As you may very well know, LTO has had a spate of particle problems
lately.  The initial particle problem which put the system down a few
weeks ago has been resolved, so is not the issue now.  This latest
series of particle problems has a different signature.  This is what we
think we know so far.

It appears that the particles are actually pieces of film flaking off
the tube and quartzware.  The feeling is that the flaking/peeling is a
film adhesion or film stress issue.  This seems to coincide with a more
frequent use of thick films deposited at 450 C, which is a higher temp
than most other processes here.  In fact, just before this last
instance, one user deposited eleven (?!?) microns of LTO at 450 C.
Before the previous instance, a user did two consecutive depositions at
450 C of three microns each.  Gladys will be checking into the logs to
see if thick depositions at 450 C do, indeed, correlate with
peeling/flaking.  If any of you has information on the film parameters,
particularly film stress, for this 450 C process, PLEASE contact Gladys.

Our alternative theory is that our process has drifted off the hairy
edge (or rather, peeling edge.)  Jim McVittie, Ray, and Mike, did some
mass flow controller calibration checks which show that our gas flows
are considerably off -- it isn't certain whether they have always been
off by this amount or if we've slowly drifted this way over time.
Gladys and Nancy are in the process of running tests using programs with
corrected flows, which will be compared to current values.

The tube is otherwise functional (good uniformity, good deposition
thickness).  The maintenance folk will be doing a tube pull and clean,
but it is not certain when they can do this (tylan nitride is supposed
to go tomorrow.)  Until then, if you do not care about particles, the
tube is usable.

When the tube is changed and the process is brought back up, we are
going to ask those of you who wish to deposit LTO at 450 to talk with
Gladys before doing so.  This is not to say labmembers cannot run thick
450 C LTO, but I'd certainly feel better (and I'm sure other LTO users
as well) if we knew for certain this was not going to be a problem.  To
those of you who run this process:  we would appreciate it if you could
provide information about this film and maybe even help us design and
run experiiments (if necessary) to characterize this process.

Just as a note -- there is a policy limiting deposition thicknesses in a
single run to 3 microns.  Thicker runs (such as the 11 micron dep
described above) go against stated policy.  As there appears to be a
general need for thicker films, we will probably have to revisit this
policy -- those of you who need thick films, please work with us on
this.

In summary:

1.  We think that the particle problem may be caused by an increase in
the number of thick 450 C depositions.  Gladys and Nancy are collecting
data.
2.  The tube will be pulled & cleaned, but timing is uncertain because
of other furnace issues.  Until then, LTO is pretty junky, but OK to
use, if you don't care about particles.
3.  When LTO comes back up, please DO NOT RUNS 450 C thick depositions
(how thick is thick?  I don't know, but will arbitrarily say "one
micron" for now.)  Help us get more info on this before we risk
prematurely junking up another tube.

Mary


--
Mary X. Tang, Ph.D.
National Nanofabrication Users' Network
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
(650)723-9980
mtang at snf.stanford.edu





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