From Beth Pruitt (thanks!):
"If you're going to use this more than once,
a [silicon shadowmask] wafer can be quite fragile and instead of spending
the $$ on the photomask and the time on the STS, if you can afford it
(about $750 for a bi-layer Be-Cu mask I think) try Photosciences... I've
attached guidelines [below] I created from my interactions with them,
I don't know why they don't have them, but these design rules will help
you talk to them about what you can and can't do. there are other companies
that create the mask by plating it up and they can achieve submicron features
in theory, their masks are closer to $5K though."
Photo Sciences guidelines for Shadowmasks, as
defined by Beth Pruitt.
Design Format: Files can be provided in GDS,
dxf, dwd format. There is a setup and conversion charge to create a master
mask from your design file.
Size: To work with the EV alignment fixture,
the footprint is circular and should be no larger than 100mm but at least
97mm in diameter. Your pattern should extend no further than about 85mm
in diameter. These limits are for the vacuum lines on the chuck. Photo
Sciences can build masks with tight spacing and small features, but they
may be too fragile to be practical, the more supporting material you have,
more robust the mask will be.
Single metal masks:
- isotropic etch from one or both sides defines
pattern as shown. Resolution not as good as bi-metal but they are less
expensive. Get good resolution with thinner masks, but they are more
- Edge definition is crisper while mask can
be thicker and more robust.
Resolution: (see cartoon below)
- Depends which kind of mask you choose and
mask thickness. Typically can resolve 2.5 micron open features within
about +/-1microns, call for tighter tolerances. Features will have rounded
corners from the etch process.
- "Bridges" in the mask must be at least 50microns
and will be more robust if over 100microns. Long bridges -- greater
than about 2:1 aspect ratio won't hold up well, short runs of tight
spacing are ok if there is enough material around them.
- Alignment Marks: better to have an all open
design for alignment to existing crosses than flimsy crosses with "bridges"
More from Neville Mehenti (thanks!)
1. Photo Etch Technology (www.stencil.com) 978-805-5050
They make their shadow masks in stainless steel, and the masks are 2-25
mil thick (50-625 microns). They define their features either through
chemical etching (if feature is >4 mil), or laser cutting. As for data
preparation, most drawing formats are accepted, and if you have a simple
geometry or array, a hand drawing with dimensions is acceptable as well.
A 15x15 inch steel patterned sheet can cost in the ballpark of $250 if
it is chemically etched. (Yes, so you can get about 16 masks from this
2. Photo Sciences 408-748-7673
This company charges a bit more, but can do a better job if you need smaller
features. For features over 5 mil, they use stainless steel. But for smaller
features (a few microns), they can make fine edges by using a bimetal
Ni/Be-Cu mask, but the structural integrity of the mask then becomes a
concern. They take all drawing formats, but may charge for data conversion.
A 4x4 inch mask made in stainless steel can cost about $500. Roger Horstman
is the guy to talk to at this company, he is very helpful.