Specific Process Knowledge/Etch/Etching of TOPAS
Etching of TOPAS 
TOPAS is etched by an oxygen plasma in the ASE. Masking of TOPAS was achieved by photo resist or a hard mask of aluminum or silicon. Photo resist is the preferred masking material, since hard masks tends to introduce local masking due to redeposition. TOPAS can be etched at rates up to 500 nm/min, with excellent uniformity over the wafer.
| Parameter | Slow TOPAS etch | Fast TOPAS etch |
|---|---|---|
| O2 (sccm) | 50 | 99 |
| CO2 (sccm) | 50 | 0 |
| Pressure (mTorr) | 40 | 40 |
| Coil power (W) | 800 | 720 |
| Platen power (W) | 60 | 60 |
| Temperature (oC) | 20 | 20 |
| Etch rate (nm/min) | ~350 | ~500 |
| Center-Edge uniformity | 0.98 | 0.95 |
Under etching and local masking
When etching TOPAS I have in general used a hard mask material underneath my layer of photo resist, to ensure that if the resist was completely removed, a mask was still present. It is however always recomended to have a photo resist as mask, as a hard mask material will introduce roughness in unmask areas of the polymer.
| Silicon hard mask | Aluminum hard mask |
|---|---|
|
|
| Etch broke through the photo resist layer, and sputtered silicon have redeposited on the polymer surface, introducing local masking effects. | The aluminum hard mask has been etched in the resist developer introducing poor edge definition even though the resist was not completely removed by the etch. |
Etch
|
Etch
|