Specific Process Knowledge/Lithography/4562
Resist description
AZ 4562 is a positive UV photoresist for thick coatings (above 5µm).
Priming
HMDS priming is recommended for improved adhesion.
Spin coating
Typical spin parameters:
- Spin off: 30-60 s
- Soft bake: 300 s @ 100°C in proximity
The thickest achievable coating using a normal spin cycle is probably 10-15µm. However, reducing the spin-off time to a few seconds at 2000 rpm, has successfully been used to increase the coating thickness beyond 20 µm on a Gamma coater. The substrate waits for 1 min before softbake, in order to reduce the edge bead height.
Exposure
Before exposure, the resist must be rehydrated:
- A 1-2 µm resist film requires less than 1 minute
- A 6 µm resist film requires 15-20 min
- A 10 µm resist film requires an hour, or more
After exposure, the nitrogen generated in the resist film must be allowed to diffuse out, in order to avoid bubble formation (in particular before any heating). This process is similar to rehydration, but usually slower.
Exposure in mask aligner: In order to avoid heating during exposure, leading to the formation of bubbles, it is recommended to use multiple exposure, limiting the exposure time for each cycle to 10-15 s, and using a 10-15 s pause between cycles.
Development
Development speed:
- Puddle development in 2.38% TMAH (AZ 726 MIF): ~2 µm/min
The recommended development speed in 2.38% TMAH (AZ 4726 MIF) for AZ 4562 is 2 µm/min. A 6.2µm resist film thus requires ~3 min development, recommended as three separate 60 s puddles. 10 µm AZ 4562 has successfully been developed using 4 x 60 s development.