Direct-Write Lithography Recipes
Maskless Aligner (Heidelberg MLA150)
For CAD design tips and requirements, see these pages:
- Design Guidelines + Tips - useful info for designing your CAD files, alignment marks etc.
- CAD Files and Templates - example CAD files etc.
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 955-1.8 | 4 krpm, 30s | 95°C, 90s | ~ 1.8 µm | 405 | 210 | 10 | 110°C, 90s | AZ300MIF | 60s | Used UCSB design (1um dense lines) | |
| 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
** To use AZ5214 as a negative PR requires Flood Exposure with the MA6 or MJB aligner after PEB, before developing. See here for a basic AZ5214 process, it is different than typical negative resists. | |||||||||||
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:
|
| 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. | ||||||||||||