Effect of Chromium–Gold and Titanium–Titanium Nitride–Platinum–Gold Metallization on Wire/Ribbon Bondability

Gold metallization on wafer substrates for wire/ribbon bond applications requires good bond strength to the substrate without weakening the wire/ribbon. This paper compares the ribbon bondability of Cr-Au and Ti-TiN-Pt-Au metallization systems for an optoelectronic application. Both Chromium and Titanium are used to promote adhesion between semiconductor substrates and sputtered gold films. However, both will be oxidized if they diffuse to the gold surface and result in the degradation of the wire/ribbon bondability. Restoring bondability by ceric ammonium nitrate (CAN) etch was investigated. Experiments were conducted to investigate the effect of Cr-Au and Ti-TiN-Pt-Au, annealing, and CAN etch processes, on 25.4times254 mum (1 times 10 mil) ribbon bonding. All bonds were evaluated by noting pull strengths and examining specific failure modes. The results show that there is no significant difference in bondability between Cr-Au and Ti-TiN-Pt-Au before the annealing process. At this point, excellent bond strength can be achieved. However, wire/ribbon bondability of Cr-Au degraded after the wafers were annealed. The experimental results also show that a CAN etch can remove Cr oxide, and that the improvement in wire/ribbon bondability of Cr-Au depends on the CAN etch time. It is further demonstrated that the same annealing process does not have a significant effect on the bondability of Ti-TiN-Pt-Au metallization on the same type substrate materials. Auger electron spectroscopy was used to investigate the causes of the difference in bondability between these two metallizations