Direct-Write Lithography Recipes

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Revision as of 14:13, 17 July 2024 by John d (talk | contribs) (→‎Greyscale Lithography (MLA150): moved SPR comments to own row, was squished into small column)
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Maskless Aligner (Heidelberg MLA150)

For CAD design tips and requirements, see these pages:

Photolithography Recipes for the Heidelberg MLA150. All recipes were characterized on blank Silicon wafers. For different substrate coatings/materials, you will likely need to run a focus-exposure matrix ("series" exposure mode), using our params as a starting point.

These recipes use the same spin and bake params as our contact aligner and stepper recipes, using built-in hotplates on the photoresist spinner benches.

Any I-Line PR is usable, although we only characterized a select few below. Run your own Focus-Exposure Matrix to characterize a new PR.

Note: On this tool, it is common to have to run a Focus-Exposure Matrix (aka. FEM), via "Series" exposure mode, for each new layer structure and/or critical feature size. The layer structure can strongly affect the exposure parameters. See the FEM Analysis Tips page for how to choose the proper exposure parameters.

The MLA Troubleshooting > Out-of-Focus Exposures section can help you avoid bad exposures, please read it!

Positive Resist (MLA150)

We found that positive PR's worked well with the 405nm laser - the 375nm laser would likely also work. Sub-micron features are possible. Overexposure is recommended to avoid stitching and horiz/vert discrepancies; compensate for widening/narrowing using CD Bias as described here.

Note: calibrations done with the "HIMT design" will show higher dose, due to using only dark-field line/space patterns.

Resist Spin Cond. Bake Thickness Laser (nm) Exposure Dose (mJ/cm2) DeFocus Rehydrate* PEB** Developer Developer Time Comments
AZ4110 4 krpm, 30s 95°C, 60s ~ 1.1 µm 405 240 5 none AZ400K:DI 1:4 50s Used HIMT design (good for isolated lines 0.8-1um)
AZ4330 4 krpm, 30s 95°C, 60s ~ 3.3 µm 405 320 6 none AZ400K:DI 1:4 90s Used HIMT design
AZ4620
SPR 220-3.0 2.5 krpm, 30s 115°C, 90s ~ 2.7 µm 405 325 - 4 115°C, 90s AZ300MIF 60s Used HIMT design. 0.6-0.9µm line/space.
SPR 220-7.0 3.5 krpm, 30s 105°C/2min

Cool 1min

~ 7.0µm 375 ~550mJ -20 >1hr 115°C, 90s AZ300MiF 70s Rehydration after exposure is necessary, to prevent bubbles at PEB.
SPR 955-CM0.9 3 krpm, 30s 95°C, 90s ~ 0.9 µm 405 250 - 7 110°C, 90s AZ300MIF 60s Used HIMT design
THMR-3600HP 1.5 krpm, 45s;

250 rpm/s

100°C, 60s 0.430µm 405 180–220 -4 100°C, 60s AZ300MiF 20s ~0.4nm line/space:

lower dose for clear-field, higher dose for dark-field.

*Rehydration: After exposure, leave sample in lab air (ok to cover in tray, with tinfoil). Allows water vapor in air to diffuse into PR to complete chemical reaction.

**PEB: Post-exposure bake: after exposure, before develop

Negative Resist (MLA150)

We found that all the negative PR's we tested required the 375nm in order to be fully exposed with reasonable dose/time.

Resist Spin Cond. Bake Thickness Laser (nm) Exposure Dose (mJ/cm2) DeFocus PEB* Flood* Developer Developer Time Comments
AZ5214 6 krpm, 30s 95°C, 60s ~ 1.0 µm 375 35 - 5 110°C, 60s 60" AZ300MIF 60s Used UCSB design. Good for up to ~1.3um open line space.
AZnLOF2020 4 krpm, 30s 110°C, 60s ~ 2.1µm 375 340 - 3 110°C, 60s none AZ300MIF 90s Used UCSB design. Good for 2um open line space.
SU-8 2075 ~70µm 375 Extremely viscous. Pour into a wide-mouthed bottle, dispense directly from bottle. Replace napkin at end.
*PEB: post-exposure bake. For AZ 5214-IR, this performs Image Reversal, and requires Flood Exposure with the MA6 or MJB aligner afterwards, before developing.

Greyscale Lithography (MLA150)

AZ4620 is the manufacturer-recommended PR for greyscale litho.

Please see the MLA150 - Greyscale Design Guidelines & Limitation

Resist Spin Cond. Bake Thickness Laser Exposure Dose (mJ/cm2) Focus Offset Rehydrate* PEB** Developer Developer Time Reflow*** Comments
AZ4620 ? krpm/30” 95°C, 60” AZ300MIF 60s To Be Added
SPR 220-7.0 3.5 krpm, 30s 105°C/2min

Cool 1min

~ 7.0µm 375 ~624mJ to clear large mm-area,

520mJ to clear ~5µm lines.

-20 ≥1hr 115°C, 90s AZ300MiF 70s TBD Author Credit:
  • Patrick Curtis, 2022
  • Biljana Stamenic 2023
  • Demis D. John 2023
Notes on SPR 220-7 Greyscale: Rehydration after exposure is necessary, to prevent bubbles at PEB.

Stitching leaves ridges in Y-direction with ~5% height of removed PR depth. Can be reduced via reflow, but significantly affects PR profile.

Author Credit: Patrick Curtis, 2022 & Biljana Stamenic 2023 & Demis D. John 2023; Please see our publications policy.

*Rehydration: After exposure, leave sample in lab air (ok to cover in tray, with tinfoil). Allows water vapor in air to diffuse into PR to complete chemical reaction.

**PEB: Post-exposure bake: after exposure, before develop

***Reflow: To smooth out stitching lines. Will change sharp vertical profiles considerably, only good for gradually-sloped profiles.