Hi All,

I'm trying to solder AuSn bumps on Cr/500nm Au metallization, which is directly
on silicon. For some reason, the wettability of the solder to the pad is very
poor. It looks like there is some passivation layer on the surface of the
metallization pad.

The wafers with the Cr/Au metallization pass the following steps before
soldering:

1. Metallization (lift off, EB evaporation)
2. DRIE device and Handle
3. PECVD of silicon oxide on the metallization side
4. BOX and PECVD oxide etch by BHF
5. Wafer clean: EKC, Pirhana, SC-1

Does anyone have any ideas about what can cause the soldering problem?

Regards,
Meni