E-beam evaporation of gold

[Semimaker]

I know this is a bit off the wall for a computing forum but I know you guys and gals have wide experiences.

I am currently working on gold spit being deposited by electron beam evaporation onto a Platinum coated wafer.

What we believe the problem to be is that an organic surface is forming on the liquid gold and so occasionally causes the gold to bubble and spit at the wafer which causes problems for the electrical circuit.

Thanks in advance as I know this is a bit strange, but I wouldn?t ask you if I didn?t think you could come up with an answer.

Any ideas on what I can do or what the problem really is?

Cheers.

 

[pm]

I have some faint experience with this. Wingznut Pez works in a fab, he might have insights too.

What are the symptoms of the problem? Imperfect coverage? (ie. gaps) Non-uniform surfaces? (ie. hills and valleys) Non-ideal resistivity? I'm not familiar with the term "gold spit" as well. It's certainly descriptive.

 

[Semimaker]

It is a small gold lump on the surface of the wafer, about 0.5 micron in size.

These either stay on the surface or fall off and produce a small hole in the gold.

 

[pm]

500nm? Wow. That's tiny. Much smaller than I would have thought considering the surface tension of liquid gold - which is ~10x that of water IIRC.

Is it possible to adjust the rate of deposition? Do they get larger or smaller as you adjust the rate? Or more or less frequent? If your hypothesis is correct, then you could guess that as the rate of deposition increases, the problem might increase as well.

It's all a bit out of my area. I worked with GaAs and InP back in my graduate studies, but I haven't had much direct experience with non-Si manufacturing materials since then (medium concentrations of Au and Si circuitry do not get along very well).

Have you check through research papers?

I wish I could help - it sounds interesting.

 

[Semimaker]

Cheers pm,

Yes I know it is very small these spits, but they are lying on a 0.5 micron gate which optically you can not see if there is a spit on the surface or a hole. The only way to find out for sure is to SEM it and this is not practical. I have tries lowering the deposition rate form 10 A/sec to 5 A/sec, this have reduced the number of spit but not to a level where the problem is insignificant.

Thanks for your thoughts, I don't think that the GaAs is sinificant though as I have seen these on Si as well.