I would use a low power oxygen plasma instead. Make sure that the power is low enough as not to heat up the gold electrodes too much.

If you are going to use piranha be careful, because fresh and hot piranha can damage the gold layer. With 40°C hot piranha, one minute is enough to remove photoresist, or you can also try 50-60 °C hot Dimethyl-Sulfoxide in ultrasonic. After rinsing with water or isopropanol I always dry the wafer with compressed air or with nitrogen.

We do this all the time - and with that exact resist too. We remove AZ 1518 from chromium-glass masks. We heat the Piranha to 120 degrees C and leave the substrate in Piranha for several minutes to half an hour.

We always have excellent results, so this is a method I highly recommend, as long as your substrate isn't etched by Piranha (such as glass, silicon, chromium, and noble metals).

You can use Piranha to clean the gold substrate. However, please make sure that the mixture ratio between H2SO4 and H2O2 is 4:1 (%Vol). You can remove the AZ1518 photoresist by heating the Piranha up to 120 degree Celsius for 10-15 min. Then rinse the sample with DI water. The ashing process with oxygen plasma is the other choice to remove a photoresist from the metal layer.

Microposit remover 1165 should do the job. Use it @ 50°C to get rid of the photoresist. If you can do ultrasonication, it can help to remove the resist much easily. See this procedure from stanford nanofacility where they have explained in their last section under "lift-off" using 1165 remover. Also, as mentioned in their link, be sure that the temperature is controlled well as 1165 remover has a flash point at 85°C.

https://snf.stanford.edu/SNF/processes/process-modules/photolithography/lift-off-lol-procedures/liftoff

Never use Piranha solution on substrate that has metal e.g., Ni, Au, Cu etc. There will always be damage to metal. Use of Acetone is a standard procedure to remove the photoresist and I was doing it routinely when doing Photolithography. Alternately you can use Plasma treatment. But using acetone should take only minutes to remove the photoresist.

You can use a product called Nanostrip available from Cyantek. Basically it is stabilized Pirahna you can pour from the bottle. Much safer than mixing your own. We use it all the time to remove resist residue and it works at RT. It can also be heated to 70C if needed.

Thatshould work. As Piranha just attacks organics your device should be fine. I have used this to remove severely damaged resist after plasma etc or ion implant. However, I would think about other causes of the cloudy surface. Do you use squirt bottles to apply the IPA? I know that acetone will degrade plastic squirt bottles and needreplacing after a short time. At any rate, I would say the piranha should work for you.

For thin and small gold electrodes, the oxygen plasma after acetone cleaning is preferable: RF power is in range of 60-100 W, time is 30 -60 sec, oxygen flow is 60-100 sccm.

Dear Silvan

Which power and how long did you use with oxygen plasma?

Thank you so much.

Anh

Dear Gianmario

On top of our Gold electrode, there are some structures by SU-8. I coated AZ 1518 to protect Gold surface during the dicing process. After finish, I have already clean by Axetol in ultrasonic 3min, Isopropanol and water but it seem the surface still not totally gold. So I would like to use piranha to clean.

Can I use in room temperature? And as Marik recommend, is 1 min enough?

Thank you so much.

Anh

Hey Anh,

if you have SU-8 patterns which you want to preserve, you might want to be cautious with Piranha. You could try to use it at room temperature - if you do, you should use an iterative process:

- Piranha for 1 min

- rinse with DI water

- check with optical microscope

- if AZ 1518 still in place, repeat Piranha treatment

Sri Ram above mentioned using Microposit remover 1165. I personally have no experience with it, but a colleague of mine mentioned it as a possible solvent for Novolak-based photoresists that have been excessively cross-linked (too long hard bake, or hard bake at too high temperature). So that might indeed be an option worth considering.

Depending on the thickness and the size of your gold patterns, piranha can eat the gold up. Hence, I suggest you try the piranha on a test sample first in case you compromise your patterned devices.

My favorite for removing photoresist are the NMP based removers (Remover 1165 and Nanoremover PG). They can be used from room temp to 80C with or without sonication and are relatively safer for the user. Do not use these on materials that are sensitive to bases (such as aluminum or copper); use AZ Qwick Strip for those. All can be rinsed with water.

If that does not work then that means I did something awful to the resist (or it is not resist residue). Then it is on to the ACT series (ACT 935 for example), but you have to choose wisely.

Oxygen plasmas are not always safe depending on the system you are using. An O2 plasma will change the surface chemistry of the SU-8. Test first.

By pure chance I was reading through the Microchemicals documents, and found that the AZ 1500 series resists are removed with AZ 100 Remover. Now the interesting thing about the AZ 100 is that the manufacturer documents the fact that the AZ 1518 hard baked at 190 deg. C can still be removed with AZ 100.

If you need, I have the documents from the manufacturer, or you can request a username and password from Microchemicals and access them online.

Dear Gianmario

Thank you so much for your help. I have already try with Piranha in 1min at room temperature but it seem to affected SU8 structrure. Could you send me that documents?

Best regards

Anh

Hello, does anyone know which is the best way to remove IP-dip avoiding damage of the Ni substarte?

Thank you and best regards