We are trying metal assisted chemical etching in our lab. Since the metal layer for this purpose needs to be too thin (few nm), the adhesion of metal to the silicon substrate is poor. We observed that a few nm of gold comes out when we rub the wafer surface gently with hand. We can't use any adhesive layer like chromium since it will not help in metal assisted chemical etching. Silver and platinum could also be used for this purpose. Anyone has good exposure in this area to suggest best metal that can be used?
Hey Jose,
It depends on what you are trying to do (and how you are getting the metal onto the surface), but there are a couple of strategies you can use. If you are trying to deposit gold nanoparticles onto the surface to use as an etching catalyst, it's good to use a polylysine coating. In the past we have used a plasma cleaning step to leave hydroxyl terminated silicon, then coated with dilute polylysine, before adding gold nanoparticles onto the surface. Alternatively, if you use something like spin coating, you can get a good layer as well. If you are going for a sputter coating deposition then you should be fine going straight onto the silicon waffer. Depending on the etchant you are using, then silver should also work just fine for etching, and is one of the more commonly used methods.
Lysine or any other oxygen/hydroxyl bonding agent will improve adhesion of gold to silicon. The J.F. Zimmerman is correct in this aspect. But thiol-containing silane coupling agent is the most reliable solution. Silane group bonds to silicon and thiol to gold. No decomposition up to 160C temperature.
You can use copper as intermediate metal
Another solution is using a primer such as Silane
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