Characterization Results of SU8 Process (obtained in MSAL)
Table: Optimized processing parameters for SU-8 layers with different thickness
Thickness Resist grade Spin coating Pre-bake Exposure dose Post-bake Developing Resolution
m
rpm/sec
C/min
mJ/cm2
C/min
min
m
41.5
SU-8/50 500/15+3000/15 95/30
450
95/30
4
10
21.8
SU-8/50 500/10+4000/30 95/45
330
95/30
8
10
8.0
SU-8/5
500/10+1500/20 95/30
250
95/30
3
4
5.8
SU-8/5
500/10+2000/30 95/20
200
95/20
3
4
Note: If cracks are found in SU8 layers, you may bake them @100C for 5 minutes to reduce the number of
cracks efficiently.
Dimentional Change %
The effects of exposure dose on dimensional change for
different size transferred patterns
2
1.5
1
Structure A (500 um)
Structure B (85 um)
0.5
0
-0.5
-1
-1.5
230
250
270
290
310
330
350
370
Dose (mJ/cm2)
This figure shows the relative dimensional changes as the function of exposure dose for two different size
patterns. For each structure size, there is a zero dimensional change exposure dose for this 8 m thick SU-8
resist. At lower dose, because of no sufficient photo-initialized acid to fully cross-link the resist, the
material may be washed away by developer. On the other hand, at higher exposure dose, the enhanced acid
concentration plus the enhanced diffusion will cause cross-link at vicinity area of the designed patterns
resulting in the expanded SU-8 structures. Since the dimensional changes are relatively small, the results
also suggest that if all structures in a mask have close dimensions, we can apply an optimized exposure
dose applicable to whole wafer.