Download Process and Information Document - Liquid Crystal Institute, Kent

Process and Information Document
#A-108
Cleanroom Facility, Liquid Crystal Institute, Kent State University, Kent, Ohio
Mask Cleaning
There are several different types of masks used in the cleanroom. There are in-house
printed black wax on transparencies, photoemulsions on plastic sheet, and chrome on
glass.
The in-house printed masks are a few dollars each, but the wax does not adhere well to
the plastic and many pinholes will be present and more will develop over time as the
masks are used. These are used for quick and dirty low resolution imaging, and should
not be cleaned except with ionized air blow off. Solvents and any mechanical handling
of the wax pattern will cause it to come off. These can be reprinted as needed.
The plastic film photoemulsions are about $100 each. They have much better adhesion
and can be designed to do resolutions up to about a minimum of 25 um feature size.
These can be cleaned, but extreme care should be taken to protect them from excessive
rubbing and solvents like acetone. IPA can be used to gently wipe them down if
necessary. The films may swell in the presence of IPA or Methanol temporarily so if
used for high res work, they must be placed under vacuum for a couple of hours at no
heat following wet cleaning. These masks, if damaged will have to be reordered with a
two week lead time time for replacement, if the drawing file is still on file.
The glass chrome masks cost about $1000-2000 each. In many cases these masks were
designed for specific projects that have long ago ceased. The original drawing files for
these may not be able to be located should one of these break. Also, funding may not be
available to replace broken glass masks. However, these masks can do much higher
resolution patterns and stand up very well to washing. Mechanical rubbing and all of our
normal solvents will not damage these. But, acid will etch the chrome and sharp razor
blades can scratch the surface. The highest resolution masks can be ultrasonically
cleaned if desired. Masks should be wiped down with acetone along the direction of the
primary lines and thoroughly rinsed and then blown off. Then they should be subjected
to low heat and possibly vacuum to remove small amounts of water from the mask
surface before use. At this time, permission must be granted for users to use
chrome/glass masks. Also, only facility staff are currently authorized to wet clean
chrome/glass masks. Users may use ionized blowoff air to blow off any visible particles.
The above information is intended to give a general overview of the process and not
enough information has been given for anyone to clean masks without additional formal
training and certification. Should you need to do mask cleaning, please request formal
training from facility staff. Training sessions are scheduled as staff have time and you
may have to wait a week or so until a time slot can be created and to allow for multiple
users desiring the same training to be assembled into a group.
Only Cleanroom Staff are allowed to train users on the use of cleanroom facility
equipment and processes. Please do not ask others in the department, your company or in
your research group to assist you to avoid formal training and certification. If training is
given by unendorsed individuals, both the trainer and trainee will lose cleanroom use
privileges for a period of time deemed appropriate by facility staff.