Photolitho20231109

Day1

• Cleaned 2 wafers with acetone, isopropanol + VWR hot plate
• 1 wafer: the SU8 did not spread well (discarded). We need a spatula for spreading SU8
• Cleaned another wafer with isopropanol + plasma
• After SU8 spin coat and 1 hr's rest, the second wafer appears with multiple bubbles. Both wafers have SU8 bulged up at the edge.
• Targeted hickness 50 um, so we used the parameters from Ali's protocol (same as table from GM1070 data sheet):
• Spin coat speed: 1700 rpm
• Relax time: 1 hour
• Pre-bake: 15 min@65°C, 2 hours@95°C. (P --->Temperature: Pr.51 65->P --->Time: Pr.t1 15->P --->Temperature: Pr.52 95 ->P --->Time: Pr.t2 99.99->P ---->Temperature: Pr.53 95->P ---->Time: Pr.t2 20->P)
• Caution when setting up the program for pre-bake: 1) When you turn on the hotplate, immediately press U until the flashing green dot is gone. Otherwise, the temperature will rise very quickly. 2) Even if you did step 1, during setting up the program, the hotplate may heat up again. To avoid that make sure the initial program Pr (before Pr.51) is set at 22°C. 3) Make sure the temperature after Pr.53 is set to at 22°C.
• We kept the wafers on hotplate and came back next day

Day 2 20231110

• Came back to hotplate and noticed the temperature was maintained at 65°C (Refer to Caution No,3))
• Take out the plates and cool down for 10 min. Caution when turning on the LAF cabinet when handling SU8, the white light inside the LAF cabinet will automatically turn on after 3 min. Do not handle SU8 before you switch off the white light.
• Set up the UV KUB 2 for exposure. Wafer with SU8 side facing up, mask side???. (We used the same mask for 2 wafers)
• Exposure dose: 200~400 mJ/cm2 (divide the number from the datasheet, 800, by factor 2 to 4)
• Exposure time: 20% power, 25s, see below how it is calculated.

Exposure dose of UV KUB 2 measured by Mathias with dosimeter (2020) for 100% power is

Exposure time [s]	1	2	5
Dose [mJ/cm2]	45	93	235

We need 5s at 100% power->235 mJ/cm2, WE USUALLY expose with 20% power, so we multiply the time by 5, 25s

• Delay time: 10 min
• Post-bake: 15 min@65°C, 40 min@95°C
• Develop in PGMEA: 4 min
• Hard Bake using VWR hot plate 2 hours@135°C

Day 3 PDMS baking on 20231115

• Results: all shapes look good by checking the PDMS stamps, except for the smallest double-rings
• Interferometry to be done