[labnetwork] Susceptor for RTA

[Matt Dwyer]

Hi all,

 

I recently acquired a graphite/SiC susceptor for 3” wafers from Allwin21 for
annealing GaAs samples in our Heatpulse 610 RTA and would like to solicit
advise on proper use. Due to the expense and leadtime of a new susceptor, I
would like to take every precaution as we develop this process.

 

Anneal temperatures will be on the order of 400 to 450C, holding for up to
60s. I will be annealing small pieces (4x8 mm^2), ¼ 3” wafers and very
rarely 3” wafers.

 

I have been reading through RTA SOPs that mention susceptor usage.

 

KU <https://wiki.nbi.ku.dk/cleanroom/AccuThermo_RTA>  recommends a ramp not
exceeding 15C/s, and to not heat the susceptor without a sample inside.

Louisville
<https://louisville.edu/micronano/files/documents/standard-operating-procedu
res/RTPSOP.pdf>  recommends inserting the TC 1cm into the susceptor chamber.

IITB <http://www.cen.iitb.ac.in/slotbooking/SOP/164_SOP.pdf>  has an
appendix on susceptor usage. They say to never submerge the susceptor in
liquid, but suggest certain chemicals for cleaning (with wipes?).
Additionally, they suggest changing the wafer type to susceptor in the
recipe.

Allwin <https://www3.nd.edu/~ndnf/facilities/manuals/Allwin%20manual.pdf>
manual gives instructions on susceptor calibration and recipe creation.

 

Our tool runs Allwin21 RTA-610 V7.85C, for reference.

 

Questions

1.       Is it necessary to run a lamp/chamber calibration for the
susceptor, or can one get away with the existing wafer cal?

a.       Assuming a recipe with 60s ramp (<7C/s) and 60s/400-450C hold.

b.      Is there any risk with running a conservative recipe (above) and
looking to see if wafer-cal undershoot is manageable?

c.       Is it ok to have the cal be at low powers (i.e. <10%) since the
process temp is so low, to prevent potential damage/wear?

2.       Can the susceptor be empty during calibration and/or when running a
recipe?

a.       I assume calibrating empty would lead to minor undershoot with a
sample due to increased thermal mass w.r.t. the calibration.

b.      Any idea why KU warns against running without a sample?

3.       Should a ramp down be specified to control cooling?

4.       Can the TC be touching the backside of the susceptor as is done
with a silicon wafer?

a.       I don’t think I can set up the TC any other way as this would
affect other users of the tool.

b.      I am happy to reduce the ramp rate further if necessary.

5.       Is O2 plasma safe/sufficient for cleaning?

a.       I’d prefer to avoid wet cleaning as the increased handling
increases risk of accidental damage.

b.      The susceptor will be used by a single user for GaAs MMICs.

 

Any other advice on susceptor usage would also be greatly appreciated!

 

Thanks in advance,

Matt

PhD student

UW-Madison

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