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: 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.

E-Beam Lithography Recipes (Raith EBPG 5150+)

Electron Beam Resists Available

EBL Resists are custom-mixed according to user resolution needs - contact Bill Mitchell to get a bottle.

Currently available at UCSB are:

• PMMA: (950K in anisole, 950K in MIBK, 495K in anisole, 50K in anisole)
  • High-resolution positive polymer-based resist with relatively poor sensitivity (resolution scales directly and sensitivity scales inversely with molecular weight);
  • Poor plasma etch resistance, hence used primarily to fabricate metal lines via liftoff processes (via a bi-layer resist scheme...low MW on bottom, high MW on top for single lines, or vice-versa for T-gate fabrication);
  • Utilizes an inert solvent developer (usually MIBK:IPA mixtures)

• P(MMA-MAA) copolymer: (low MW methyl-methacrylate (MMA) and methacrylic acid (MAA) copolymers in ethyl lactate)
  • A positive polymer-based resist with poor resolution but with significantly higher sensitivity than the higher MW PMMA resists above
  • Used primarily as the top layer in a bi-layer resist scheme for T-Gate fabrication, and utilizes inert solvent developer (MIBK:IPA mixtures)

• CSAR-62: ZEP-equivalent resist manufactured in Germany at much more competitive pricing!
  • High-resolution polymer-based positive resist with very good sensitivity and excellent etch resistance
  • Can be used in both metal lift-off processes (slight overexposure results in an excellent undercut profile) and various dry-etch processes for pattern transfer to the underlying substrate
  • Utilizes inert solvent developers (e.g., n-amyl acetate for higher sensitivity and good resolution or MIBK:IPA mixtures for increased LER performance)

• maN-2403: negative polymer-based resist (that is NOT chemically amplified)
  • Very good resolution (down to the 40-50nm range) and sensitivity
  • Exhibits excellent dry-etch resistance
  • Developed using a dilute basic solution (e.g., metal-ion-free developers such as AZ-300MIF)

• HSQ: negative resist that is based on spin-on glass material (ie, not polymer-based)
  • Extremely good resolution (features below 10nm can be resolved)
  • Etch resistance is high in Cl-based chemistries since HSQ reduces to a porous SiOx structure after exposure and development
  • Sensitivity and contrast are very dependent on developer solution used and are usually poor
    • Standard AZ300MIF developer solutions have decent sensitivity (100's of uC/cm2 at 100kV) but extremely poor contrast
    • Stronger (and toxic!) 25%TMAH solutions have much better contrast but poor sensitivity (1000's of uC/cm2 at 100kV)
    • "Salty" developer solutions using 1wt% NaCl dissolved in either 4wt% NaOH or AZ300MIF solutions have the best contrast but reduce sensitivity significantly (10,000's of uC/cm2 at 100kV)

• DUV resists: UV6, UV210 UVN-30: chemically amplified polymer-based resists
  • High resolution and excellent sensitivity (clearing doses below 100uC/cm2 at 100kV)
  • UV6 used mostly in optimized t-gate resist structures
  • Developed using a dilute basic solution (e.g., metal-ion-free developers such as AZ-300MIF)
  • Can be "double exposed" by ASML DUV Stepper and EBL.
    • Recommended to produce ASML alignment marks first for double exposure methods.
  • See ASML litho recipes for datasheets.

EBL Exposure Recipes

To Be Added - BEAMER simulation is always required for small (<<micron) features.