Specific Process Knowledge/Lithography/4562

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Resist description

AZ 4562 is a positive UV photoresist for thick coatings (5 - 10 µm).

Priming

HMDS priming is recommended for improved adhesion.

Spin coating

Spin curves for AZ 4562 using 60 s spin-off and 60 s @ 100°C softbake on LabSpin, and 30 s spin-off and 300 s @ 100°C 1 mm proximity softbake on Gamma

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 10 µm. 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

Multi-puddle development:
The recommended development speed in 2.38% TMAH (AZ 726 MIF) for AZ 4562 is 2 µm/min.
A 6.2 µm resist film 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.