SpecMat Response to PDMS Module Devlopment
edmyers at stanford.edu
Wed Jan 18 13:31:44 PST 2006
The question about running AFM Associates PDMS process in the facility was
discussed at yesterday's SpecMat meeting. SpecMat came to the following
If the PDMS starting components are electronic grade, the process is
approved from a chemical contamination point. However, we are very
reluctant to approve the process due to the concerns over mechanical
contamination of the equipment set and from concern over process capability
of the Nikon to resolve the 0.7um feature size.
The request process flow is:
Deposit and cure 500um thick layer of PDMS
Deposit 0.5um of Aluminum using Gryphon
Expose using Nikon stepper (CD = 0.7 um)
Timed etch of aluminum in P5000, down to PDMS layer
SpecMat's specific process concerns are as follows:
1) The PDMS must be electronic grade and must be mixed and out gassed
outside of the fab.
2) The ability to dispense and cure the PDMS layer with sufficient flatness
to resolve 0.7um features.
3) Complete backside PDMS edge bead removal, compatible with resolving
4) Deposition of the Al without any peeling. There is concern the
deposition could provide sufficient energy to the substrate which will
result in flaking of the Al in the Gryphon deposition chamber. If this
occurs we will be looking at significant downtime (days) to clean and
qualify the deposition chamber.
5) The ability of the Nikon to focus on the thick, transparent PDMS
layer. Someone skilled with the Nikon will most likely need to run the
samples to adjust the focus depth outside of standard
tolerances. Subsequent to running the PDMS samples, the Nikon's focus will
need to be calibrated to standard silicon substrate thickness.
6) The P5000 has a high density plasma which can significantly heat the
substrate. There is concern the heating will cause a delamination problem
between the Al and PDMS. If the wafers flake in the etch chamber we will
lose a day to clean the chamber. Hopefully, any particulation will not be
carried in to the transfer module or load locks.
There has been a number of emails exchanged recommending alternative
approaches to process development such as metal deposition in the Innotec
to minimize substrate heating during metal deposition (and easier cleaning
if the wafer peels and test the exposure) and starting with thinner
PDMS. Continued discussion on an approach to the process development is
necessary to reach a comfort zone where we can minimize our equipment exposure.
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