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AZ5214E
A positive resist that can change polarity using an image reversal (IR) bake. Image reversal can create severe undercut profiles making it ideal for lift-off purposes.
Coater: Polos Spin 150 (litho finger)
| Spin speed (rpm) | Thickness (μm) |
|---|---|
| 2000 | 1.98 |
| 3000 | 1.62 |
| 4000 | 1.40 |
| 5000 | 1.25 |
| 6000 | 1.14 |
In IR mode AZ5214E is a negative resist. The exposure is used to define areas which should be more sensitive to the IR bake. In the IR bake the exposed regions are cross-linked. The temperature of the IR bake must be carefully controlled to thermally activate the areas which have been exposed and not the whole resist.
If we skip the pattern defining exposure, an IR bake followed by a flood exposure should clear the whole resist. This we can utilize to find the temperature which below we must keep the IR bake to prevent thermal cross-linking of unexposed areas.
Low-profile hot plate (assumed to show correct value):
| Temp (°C) | 200mJ/cm^2 |
|---|---|
| 130 | NOT cleared |
| 127 | NOT cleared |
| 126 | NOT cleared |
| 125 | cleared or almost |
This indicates the right image reversal temperature to be in the interval 115-120degC.
| Temp (°C) | Acetone Lift-off |
|---|---|
| 115 | Best |
| 116 | - |
| 117 | - |
| 118 | - |
| 119 | - |
| 120 | Worst |
Second run:
| Temp (°C) | Acetone Lift-off |
|---|---|
| 112 | Best |
| 113 | - |
| 114 | - |
| 115 | Worst |
/recipes/lift-off/profile_temp.png
AZ5214E profiles for different IR bake temperatures. All samples exposed with 8mJ and developed in MIF726 for 60s.
| Exposure (mJ/cm²) | Lift-off |
|---|---|
| 6 | 3 |
| 12 | 5 |
| 18 | 5 |
| 24 | 2 |
12mJ/cm² looks to be the best balance between minimum exposure and structures smoothness.
[[/recipes/lift-off/profile_exp.png|AZ5214E profiles for 112°C (top) and 110°C (bottom) IR bakes at different exposure doses]] AZ5214E profiles for 112°C (top) and 110°C (bottom) IR bakes at different exposure doses. All samples developed in MIF726 for 60s.
The development time is probably right on, meaning slightly over (to ensure undercut).
/recipes/lift-off/profile_dev.png
AZ5214E profiles after different development times in MIF726 developer
50s at 110°C is recommended in the data sheet, but I have seen no difference between this and the lower temperature soft bake (95°C for 60s).