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 require 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. Both chromium and titanium are used to promote adhesion between substrates and sputtered gold films. Both can diffuse the gold surface after annealing and degrade 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 25.4 times; 254 μm (1 × 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 are annealed. The experimental results show that a CAN etch can remove Cr oxide. Improvement of wire/ribbon bondability of Cr/Au depends on the CAN etch time. The annealing process does not have significant effect on bondability of Ti/TiN/Pt/Au metallization. Auger electron spectroscopy was used to investigate what caused the difference in bondability between the two metallization.