Greetings.

Recently I have noticed a problem with my wire bonding. When I deposit 20nm of Ti for adherence (on a SiGe layer of a heterostructured sample) and then 200nm of Au, the wire bonding works without a problem.

I had, however, to change this process.

Now I deposit a thin layer of Ti (around 10nm) and a thin layer of Au (20nm) and then deposit some Al on part of this Au layer (the Al is for ohmic contact and it is connected to the Au just to establish contact). After annealing the sample with this structure, I deposit a thick Au layer (200nm) which covers the Al part and the thin Au layer as well. This thick Au layer is intended for wire bonding.

Imagine the thin Au layer has an area of around 100um^2. The Al layer covers around 10% of this area, so there is still 90um^2 where I have two Au layers touching each other. When I wire bond this structure, however, it became very common to peel an Au layer as if it was not well adhered. I did not expect this since I thought Au on Au should for a solid contact.

Is this Au on Au deposition expected to make a feeble contact? If not, what could be the problem?

Thank you very much.

Best regards,

Gabriel Gulak Maia