Photolithography - Manual Edge-Bead Removal Techniques

Removing the edge-bead from your substrate will help with contact litho resolution and alignment.

Razor Blade

Use a razor blade to scrape off the edge-bead regions. This works well for small samples, if the substrate material is not fragile (works well for Silicon, Sapphire, GaAs, Silica etc.)

EBR100

EBR100 squirt bottles can be found on the spinner benches. (Do NOT bring Acetone onto the spin-benches! The fumes affect nearby PR.) Only use this chemical in a fume hood, and dispose in the waste on the fume hood.

Squirt some EBR onto a COTTON swab (not plastic swab! They will dissolve.)

Rolls the swab on a cleanwipe to remove excess liquid.

Use the swab like a paintbrush to remove PR from the edge of the wafer, re-soaking as needed.

Lithographic Edge Bead Removal

For small parts, you can cut pieces of tinfoil into small squares, and mask all but 2 edges and flood expose those two edges (on a contact aligner), then repeat for the other two edges. Expose with 3-5x the typical dose, since the PR is thick at the edge. Then develop the sample to remove the edge bead. Subsequent litho will work fine.

For larger parts (eg. full wafers), you will want to make a custom plastic or metal mask that you can place on top of the wafer during flood expose - then develop to remove the edge-bead.

We do have simple metal masks made for 4-inch wafers, that you can use on the Suss MA6 with Flood Expose mode to expose your edge bead.

See this procedure for performing lithographic Edge-Bead Removal with DUV Photoresists:

ASML DUV: Edge Bead Removal via Photolithography

Demis D. John, 2022