Upload
hilda-sharp
View
214
Download
1
Embed Size (px)
Citation preview
SMEAS 2007
Bex, Rob, Georgios, Jason
Fabrication Process status
...looks like ~45% of the process is completed... Hmmm....
Fabrication Progress…• We have a total of 5 wafers• Used Innotec to deposit 50nm Au and 3nm Ti • Deposited HMDS • 1.6 μm of Shipley PR were spun• Wafers were exposed in KarlSuss2
for 1.6s in contact mode using mask #1 • Wafers developed and postbaked
Training
• Completed the following training:- wbgeneral
- evalign- MERL Cleanshop on SU-8 and PDMS spinning
• All training is complete at this point.
Procurement
• Photopatternable Silicone WL-5150 has been ordered.
BIGGEST WORRY:• Both Shadow mask and laser etch layouts
must be modified and resubmitted– so our masks may take another month!
• Additional transparency or chrome mask may be needed as back-up for previous Mask #2 plans.
SNF Shadow Mask Guidelines
Guidelines, images, and resources assembled by Beth Pruitt and available at: http://snf.stanford.edu/Process/Resources/Shadowmasks.html
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 flimsy.
Bi-Metal Masks:•Edge definition is crisper while mask can be thicker and more robust.
"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.
We thought we had this point covered! We increased our S-dimensions to avoid this sort of problem…
We thought we had this point covered! We increased our S-dimensions to avoid this sort of problem…
Minimize mask thickness to minimize feature undercutting ( thickness = .001-.002 inches )
Shadow Mask Failure Mode
Protrusions have a minimum of support with
improved geometry
Mask RedesignShadow Mask Durability
Wedges of mask material between electrodes not sufficiently supported, possibility for tears.
Mask RedesignShadow Mask Durability
Deposit twice using the same mask:
1. Deposit in colored areas
2. Rotate 180º
3. Deposit in dashed areas
Movie Time
Option 2: Laser Cut ArrayLaser Type Min. Spot
SizeCost Lead Time
CO2 50 μm $200 1 week
Nd:YAG 20 μm $350 1 week
Excimer 2 μm $500 2-3 weeks
Material• 25.4 μm gold foil• Cost: $200/device• Lead Time: 48 hours
Example of Nd:Yag Laser Cut
Mask RedesignLaser Cut Problem
100um 50um
200um100um
~50um spot size will give poor quality on 50um feature
Double wire width
8x flexural stiffness?
Mask RedesignPlan B – Crazy?
Make our own shadow mask.
DRIE of Si wafer masked with resist patterned using standard chrome litho mask.
Lots of issues
-gold contaminated
-may not be able to deposit
Redesign SummaryFeedback, please! Plan C – Not Crazy?
Shadow Mask
-Underetch problem “open” springs
-Durability problem Rotation of “half-mask”
Laser Cut
-Double width of wires, or, spend the cash for excimer.
-Cost of materials Move away from gold ($ down, stiffness up)
Own Shadow Mask
-We must be joking…
Plan C
-Lift-off, resist mask, PPS, SU8, wirebonded islands, other?