I've encountered a defect during processing that I can't figure out, so I'm hoping I might find some ideas here.
My mask design is a microelectrode array, with 60 microelectrodes with diameter 30 to 60um close together (~50-100um). I start with a glass substrate (5cm x 5cm),
- spincoat polyimide
- ALD bi-layer (HfO2, Al2O3)
- Titanium adhesion and 400nm Gold.
- S1818 photolitho to define pattern in metal
- Wet etch gold (KI/I2)
- Wet etch Ti (ammonium/peroxide solution)
After etching the Ti, I see tears in the photoresist at the edge of the microelectrodes, and in the center of the tears in the photoresist, there is a blister in the ALD that has exploded.
It appears to be related to some kind of electrochemical effect, as I don't see this phenomenon when I short circuit the contacts together before wet etching. They also seem to appear in pair of opposite electrodes.
Could it be possible that there is some charging of the electrodes which causes electrolysis of water trapped under the ALD layer, causing a blister that also tears the S1818? Or perhaps some other reaction caused by a potential difference (oxygen diffused through ALD reacting with hydrocarbon at surface???)
HF is not an option at this step, as it will also etch the ALD layer. I havent tried any other etchants either. Do you perhaps have a recipe or reference for etching Ti using oxalic acid?
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