Metal thin film adhesion, Au-Si deposition

  • #1
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What protocol should I use to get a good stable 100nm Au adhesion onto a Si substrate using electron beam evaporation? I've heard talk of primer layers of either Cr or Ti at around 5nm thickness, as the typical way to do it.

Which material should I choose? What the advantages or disadvantages of both Cr and Ti (or some other material)? They're both commonly discussed and I don't know which one to pick. (I have both available for loading sources in the lab.) When other metals such as Al is used, onto Si, it will work well with no additional adhesion layer right?

What about if Ge is used as the substrate? I know the native oxide is significantly different on Ge, it's less stable and can be soluble, compared to native SiO2. I've heard that Ge itself adheres to things well and can be used as an adhesion layer. If Ge was used as the underlying substrate (same Au deposition) could the same Cr or Ti protocol still be used (same as Si), to have confidence in reliable adhesion of the metal?
 

Answers and Replies

  • #2
Mapes
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I've used both Cr and Ti as an adhesion layer for Au to Si. The Ti was used in the context of an implantable medical device—Ti was perceived to be more biocompatible. One factor is that the adhesion layer inevitably diffuses somewhat into the Au, especially at higher temperatures, which can change the layer's resistivity, among other properties. However, I never did any rigorous tests to see whether Cr or Ti is worse in this respect. Some people insert Pt to block this diffusion. But really, the choice of Cr or Ti is a very small decision as long as your device is working correctly.

I haven't put Al on Si or worked with Ge, sorry.
 

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