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?