Could anyone tell me how to clean the surface of the ceramic substrates prior to depositing metals, where the substrate is patterned by the photoresist for lift-off? I am mainly concerned by some native Al2O3 on the substrate surface which may need to be removed through a wet-chemical cleaning technique. Usually, acids (e.g. HCl, HF) are used for this purpose as far as III-V semiconductors are concerned.
It depends how dirty your substrates are to begin with. If they are really dirty, then start by cleaning them with acetone (in an ultrasonic cleaner). Of course, you shouldn't put flammable liquids in the ultrasonic cleaner, so put the substrates in a beaker, cover with acetone, and put the beaker into the cleaner (no lid!). Once they are done, you can clean them with an acid piranha solution (10 parts DI water: 3 parts concentrated sulfuric acid: 1 part 30% hydrogen peroxide). Be VERY careful with the piranha solution and make sure you do this part in a hood. Once that is done, carefully dispose of the piranha solution, and rinse the substrates with DI water. Then, you can do a final cleaning using DI water in the ultrasonic cleaner. After this, your substrates should be quite clean.
Hi Shamsul,
You are right to be concerned about the native oxide, it is difficult to remove. Anthony is right to recommend an ultrasonic clean prior to any wet treatment.
In my experience a 10 second dip in either buffered-HF or NH4OH:DI (1:1), followed by a DI rinse and N2 blow dry, is sufficient for AlN surface cleaning prior to contact evaporation. Check the photoresist datasheet, but usually they are robust to less than ~ 2 minutes of exposure to cleaning solutions after the proper thermal treatment.
The paper below gives a good summary of GaN and AlN surface cleaning procedures, and mentions the piranha solution as an alternative. I have also found aqua regia to be very effective if you are still having problems, particularly for reducing leakage in III-nitride Schottky diode structures. Best of luck!
http://nemanich.physics.asu.edu/sites/default/files/publications/savades/1998-JAP84-5248.pdf
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Ceramics