Table 3 Details of the photolithography processes described in this work.

From: Simple sacrificial-layer-free microfabrication processes for air-cavity Fresnel acoustic lenses (ACFALs) with improved focusing performance

Photolithography process

For electrode patterning on PZT

3.5-μm-thick SU-8 adhesion layer

35-μm-thick SU-8 bottom layer

10-μm-thick SU-8 top layer

250-μm-thick SU-8 bottom layer

30-μm-thick SU-8 top layer

2-μm-thick SU-8 adhesion layer on glass

50-μm-thick SU8 mold for PDMS casting

Label for reference

A

B

C

D

E

F

G

H

Cleaning or surface treatment

Rinse with acetone, methanol, IPA, and DI water;

Blow-dry with N2.

30 s O2 plasmaa

30 s O2 plasmaa

Wipe with IPA; Blow-dry with N2.

30 s O2 plasmaa

Wipe with IPA;

Blow-dry with N2.

Piranha solutionb cleaning (20 min);

Dehydration bake @ 175 °C (30 min) on a hot plate.

30 s O2 plasmaa

Photoresist

AZ 5214 (Integrated Micro Materials)

SU-8 2005 (Kayaku Advanced Materials)

SU-8 2050 (Kayaku Advanced Materials)

SU-8 2005 (Kayaku Advanced Materials)

SU-8 2100 (Kayaku Advanced Materials)

SU-8 2050 (Kayaku Advanced Materials)

SU-8 2002 (Kayaku Advanced Materials)

SU-8 3050 (Kayaku Advanced Materials)

Spin-coating

(spin speed, acceleration, duration of each step)

500 rpm, 500 rpm/s, 5 s;

1200 rpm, 600 rpm/s, 55 s.

500 rpm, 100 rpm/s, 10 s;

3000 rpm, 300 rpm/s, 60 s;

1,000 rpm, 500 rpm/s, 10 s.

500 rpm, 100 rpm/s, 10 s;

3000 rpm, 300 rpm/s, 60 s;

1,000 rpm, 500 rpm/s, 10 s.

On 75-μm-thick PET film:

500 rpm, 100 rpm/s, 10 s

600 rpm, 300 rpm/s, 30 s

500 rpm, 100 rpm/s, 10 s;

1450 rpm, 300 rpm/s, 30 s;

Followed by thickness planarization.

On 38-μm-thick PET film:

500 rpm, 100 rpm/s, 10 s;

3500 rpm, 300 rpm/s, 60 s;

1,000 rpm, 500 rpm/s, 10 s.

500 rpm, 100 rpm/s, 10 s;

3000 rpm, 300 rpm/s, 30 s;

1000 rpm, 500 rpm/s, 10 s.

500 rpm, 100 rpm/s, 10 s;

3000 rpm, 300 rpm/s, 30 s;

1000 rpm, 500 rpm/s, 10 s.

Soft-bake (on a hot plate unless otherwise specified)

90 °C (5 min) in a convection oven

5 °C/min ramp rate

RT → 95 °C (1 min) → RT

5 °C/min

RT → 65 °C (1 min) → 95 °C (4 min) → RT

5 °C/min

65 °C → 90 °C (15 min) → RT

2 °C/min

RT → 65 °C (5 min) → 95 °C (65 min) → RT

5 °C/min

RT → 65 °C (5 min) → 90 °C (25 min) → RT

30 °C (30 min)

2 °C/min

RT → 65 °C (70 min) → RT

SU-8/SU-8 bonding

NA

NA

1 min plasma treatment on bottom layer.

Bonding in a laminator (Tamerica TCC6000) with speed level 3 @ 80 °C.

1 min plasma treatment on bottom layer.

Bonding in a laminator with speed level 3 @ 80 °C.

NA

NA

Exposure dose (mJ/cm2)

140

150 (without photomask)

120

170

250

230

900 (without photomask)

800

Post-exposure bake (PEB) (on a hot plate)

NA

5 °C/min

RT → 95 °C (hold 2 min) → RT

5 °C/min

RT → 65 °C (1 min) → 95 °C (5 min) → RT

5 °C/min

RT → 65 °C (1 min) → 90 °C (2 min) → RT

2 °C/min

RT → 65 °C (5 min) → 95 °C (11 min) → RT

5 °C/min

RT → 65 °C (2 min) → 90 °C (5 min) → RT

2 °C/min

RT → 55 °C (60 min) → RT

2 °C/min

RT → 55 °C (60 min) → RT

Development

70 s in AZ 400 K (1:4 diluted) (Integrated Micro Materials)

NA

6.5 min in PGMEA (Kayaku Advanced Materials)

2.5 min in PGMEA

22 min in PGMEA with stirring

5 min in PGMEA

NA

7 min in PGMEA

Hard bake (in a convection oven)

90 °C (15 min)

NA

NA

NA

NA

NA

10 °C/min

RT → 150 °C (30 min) → RT

10 °C/min

RT → 110 °C (30 min) → RT

  1. RT room temperature, PGMEA propylene glycol monomethyl ether acetate.
  2. aPlasma treatment condition: 35 W, 265 mTorr.
  3. bPiranha solution: H2SO4 and 30% H2O2 with a volume ratio of 3:1.
Back to article page