Lithography and Photoresists

From LPDwiki

Aliquot the PR

  • Most PRs are stored in fridge and aliquoted into small brown bottles.

1. Take out the original PR bottle from fridge. Let it recover to room temperature for at least 3 hours. Wipe away all the water condensation outside the bottle.

2. The brown bottles need to be cleaned with clean procedure B, then baked in vacuum oven >120C for 1 hour. It need to be cool down for 1-2 hour before using.

3. Pour out about 5 mL PR into waste container.

4. Pour into brown bottles.

5. Tighten the lead and seal with parafilm.

6. Store in the fridge.

Adhesion promoters

HMDS

1. Small drop of Primer 80/20

2. Wait 30 sec

3. 3000rpm 30sec

4. 115C 3 min

Epoxy-silane (2-(3,4-EPOXYCYCLOHEXYL)ETHYLTRIMETHOXYSILANE)

We can use standard silane treatment protocol: http://www.gelest.com/goods/pdf/couplingagents.pdf

1. Piranha clean the substrates, dry them completely

2. RIE: 20 sccm O2, 0.5 Torr, 33W for 20 sec

3. Soak into 2 - 4% Epoxy-silane, 5% H2O pH5 EtOH solution for 1 hour

4. N2 blow dry

5. Rinse with 5% H2O pH5 EtOH solution

6. N2 blow dry

7. Bake at 110C for 10 mins to cure

4% epoxy-silane , 5% H2O pH5 EtOH solution

1. 195 mL pure ethanol, 8.1 mL water, 183 uL acetic acid.

2. Check if the pH value falls into 4.5 - 5.5 with pH paper.

3. Add 6 mL epoxy-silane into the mixture.

4. Shake to mix.

5% H2O pH5 EtOH solution

195 mL pure ethanol, 8.1 mL water, 183 uL acetic acid.

Photoresists

Important:

  • The substrate should be cleaned then dry bake on hotplate at 200 - 250C for 15 mins.
  • If the required temperature is T, On Solitec hotplate we set the temperature to T+15C.
  • Before exposure, the film mask and support mask glass need to be cleaned with clean procedure B. During cleaning the emulsion should face up. The film mask and support mask glass should never go near to any paper or texwipe to avoid attracting fibers.
  • Film masks require vacuum hard contact on aligner to get the best result.
  • Always use UV absorption rubber sheet (red rubber) under the transparent substrate!

S1813

On rigid substrate

Tested on all rigid substrates.

1. Use HMDS as adhesion promoter for Si, glass, SiO2 …

2. 500rpm 3sec (ramp 500rpm/s)

3. 1500rpm 30 sec (ramp 1500rpm/s)

4. Soft bake 115C 2min

5. Exposure 24.9s @ 18mW/cm^2

6. Develop in MF319 for 2 min

7. Hard bake for 15 min at 115C

On PDMS

1. PETS RIE, both methods are working:

a. O2 7 sccm, 0.2 Torr, 200W 1 min. This one create micro texture on PDMS. The PDMS surface cannot be bond to other PDMS or glass.

b. O2 20 sccm, 0.5 Torr, 33W 20 sec. This one need to be used immediately.

2. 500rpm 3sec (ramp 500rpm/s)

3. 1500rpm 30 sec (ramp 1500rpm/s)

4. Soft bake 85 C 10 min.

5. Slowly ramp down to 30C in 30 mins. (might still have crack, but cracks usually disappear after exposure)

6. Exposure 16.6s @ 18mW/cm^2. Soft contact!

7. Wait 5 mins

8. (optional) Post exposure bake (PEB) 85C for 5 mins. Then ramp down to 30C in 30 mins.

9. Develop in MF319 for ~ 1.5 min. Without PEB, the developing time will be much longer.

10. Hard bake for 60 min in N2 filled oven at 80C.

SU8 2002

Tested on 1 mm glass and 0.5mm Si and 0.5 mm Si wafer with SiO2.

1. HMDS does not help SU8. We need to use epoxy-silane as adhesion promoter

2. Spin at 3000rpm for 60 sec

3. Soft bake 95C 5 mins

4. Exposure 11 sec @ 18mW/cm^2

5. Post exposure bake 95C 7 min

6. Develop in thinner-P for 1-2 min

7. Hard bake 15min at 115C

AZ5214E

Warning:

  • AZ5214E is very sensitive to storage temperature and moisture. So we need to test the parameters before actual exposure batch within 24 hours.
  • The AZ5214E has very unstable developing time. One need always keep tracking the developing result. First we can start with 60 sec (+-2sec). Check under microscope for undercuts (bright secondary edge of the feature). Then step with 10sec or 30sec depending on the actual result.

Spin coat for liftoff (2.5 - 3 micron thickness, good for < 1 micron thick sputter deposition)

1. HMDS treatment

2. 100rpm 5 sec

3. 500rpm 3 sec

4. 1000rpm 30sec


On silicon wafer for 10 micron gaps (for metal trace liftoff)

1. Soft bake: 85C 1.5 min

2. Exposure 1.3sec @ 18mW

3. Reversal bake at 85C 3 min

4. Flood exposure (no mask): Multi-exposure with 26sec + 30sec waiting, 4 times.

5. Develop for ~ 2 mins.

6. Hard bake 115C 15 mins.

On 0.5 - 1 mm glass for 10 micron gaps

1. 105C 1.5 min

2. Exposure 2.6 sec @ 18mW

3. 105C 4 min

4. Flood exposure (no mask): Multi-exposure with 26sec + 30sec waiting, 4 times.

5. Develop for ~ 1.5 mins.

6. Hard bake 115C 15 mins.

On metal layer for 10 micron holes

1. 105C 1.5 min

2. Exposure 5.2 sec @ 18mW

3. 105C 4 min

4. Flood exposure (no mask): Multi-exposure with 26sec + 30sec waiting, 4 times.

5. Develop for ~ 2 mins.

6. Hard bake 115C 15 mins.

On SiN layer for 20 micron posts (SiN liftoff)

1. 105C 1.5 min

2. Exposure 5.2 sec @ 18mW

3. 105C 4 min

4. Flood exposure (no mask): Multi-exposure with 26sec + 30sec waiting, 4 times.

5. Develop for ~ 1.5 mins.

6. Hard bake 115C 15 mins.