Posted by Seinfeld: Wed Jul 30, 2003 1:24 pm    Post subject: Contam on Bond Pad

We're experiencing ball lift issues and we think the bond pads of our lots are contaminated. But visual inspection using the microscope showed that the pads are clean. Is it still possible that the pads are contaminated? What tests do you recommend for us to check this?

Seinfeld

Posted by Memsy: Wed Jul 30, 2003 6:46 pm    Post subject:

Try EDX analysis.
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Posted by EE: Thu Jul 31, 2003 10:08 am    Post subject:

Hi Seinfeld,

At the correct EHT level during EDX analysis, the EDX spectrum will only register Al if the bond pad is clean. Given that your bond pads do not exhibit any visual anomalies, the contam may be in the form of a very thin layer of unetched glass. This would register as a peak of Si in the EDX spectrum.

Note, however, that Si may also register in the spectrum of a clean bond pad if the EHT used is too high. This is because the silicon under the aluminum bond pad is now being detected by EDX. Thus, if you see both Al and Si in your first spectrum, you must get another spectrum to verify if the SI is above or below the aluminum layer.

If it’s really unetched glass that’s on your bond pad, you will see Si and Al at a very low EHT, then see Al rising relative to Si as you increase the EHT, then eventually reach a point where the Si peak increases more quickly relative to the Al peak as the EHT is increased.

Needless to say, if you see S, P, K, or Cl on your bond pads, you don’t need to get EDX spectra at different EHT’s since you’re sure that these couldn’t have come from below the bond pad.

Thanks and keep on posting!

EE

Posted by Seinfeld: Fri Aug 01, 2003 10:35 am    Post subject:

We tried EDX at low EHT (5 keV) and saw significant silicon peak and just a small aluminum peak. We can already conclude that there's silicon contam on top of the bond pad, right?

Seinfeld

Posted by FARel Engr: Fri Aug 01, 2003 11:03 am    Post subject:

Yes, I think you can make that conclusion because a bond pad should only show Al and O at that EHT. Just a warning - using a low EHT for EDX analysis will not generate peaks of some elements, so you might not see all the elements present if the EHT is low. This is why EE is suggesting other EHT levels too.

Regards,
FARel Engr