While coating ZnO thin films on glass substrates using spin coating technique, pin holes are formed. Please suggest how to get a pin-hole free thin films.
Pinholes usually indicate localized dewetting, or micro bubbles that degas during film drying. Localized dewetting can be caused by contaminants ( dust particles in the air, crud from the operator's hair/beard (such as dandruff). So working under a laminar flow hood with protective clothing is a must.
Removing microbubbles is a more challenging task. Such bubbles can arise during solution preparation, or during the application of the coating solution to the wafer. In the latter case you can look at two methods: apply coating solution to a slowly rotating wafer or apply solution to a stationary wafer and see if there are any differences. If the solvent is highly volatile you should apply solution to a moving wafer, otherwise you are likely to get imperfections resulting from film drying during the initial spreading of the solution on the wafer.
Pinholes usually indicate localized dewetting, or micro bubbles that degas during film drying. Localized dewetting can be caused by contaminants ( dust particles in the air, crud from the operator's hair/beard (such as dandruff). So working under a laminar flow hood with protective clothing is a must.
Removing microbubbles is a more challenging task. Such bubbles can arise during solution preparation, or during the application of the coating solution to the wafer. In the latter case you can look at two methods: apply coating solution to a slowly rotating wafer or apply solution to a stationary wafer and see if there are any differences. If the solvent is highly volatile you should apply solution to a moving wafer, otherwise you are likely to get imperfections resulting from film drying during the initial spreading of the solution on the wafer.
I agree with the suggestions above. I usually filter the sols prior to coating to get rid of the dust, and for a low viscosity solvent such as ethanol, I sometimes apply a large quantity of sol to a stationary substrate, in order to cover it all. You can also repeat the spinning cycle (this works for ZnO nanoparticles), this permits to control whether you have a continuous or discrete film, see eg. Znaidi et al, Thin Solid Films
2003, 428, 1–2, 257–262 (http://www.sciencedirect.com/science/article/pii/S0040609002012191). Good luck!
Some times I have this kind of problem and depends how looks like the pinhole, maybe you must clean better the substrate. I can suggest you to use RCA process.
I more agree presence of the pinholes is mostly related to deposition technique, rate of deposition and in some rare cases quality of the prepared metal-oxide. As I've seen in other work, I suggest to follow the Murugathas solution, and if possible for u, utilizing the Spray Pyrolysis or further magnetron sputtering which is nearly available in all the universities. If the thickness of the film is important in your field of application, use the Spin coating but at the lowest speed of spinning to avoid the fuzzy surfaces.
I agree partially with Hamid, so if you really want to use spin coating, you must take care about velocity, temperature and viscosity, those parameters are very important, C. Jeffrey Brinker, George W. Scherer (Sol-gel Science: The Physics and Chemistry of Sol-gel Processing) is a good reference, check it.
Just an additional comment to those above: when we do spin coating we found that humidity plays a role, by dehumidifying the chamber and room we regularly get very thin layers with no pinholes. We are at the coast, so high humidity is a problem for us)
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Semiconductor