Overview of Metal Lifted Failure Modes During Fine-Pitch Wirebonding Low K/Copper Dies with Bond Over Active (BOA) Circuitry Design

The size of IC device has been reduced resulting from the reduction of both transistor gate length and bond pad pitch. Since 180 nm node, wafer fab technology has decreased the gate length more aggressively than the assembly site does with bond pad pitch. Both bond over active (BOA) and fine pitch wirebonding have been implemented simultaneously in order to minimize the white space area in the die. Combination of BOA, fine pitch wire bonding and low k/copper technology have thus become a new development scope for wire bonding technology development works. Several failure modes have been observed while utilizing this new technology combo. The Aluminum Cap Lift yield loss during the wirebond process was reported. The delaminated interface is Ta and copper at the aluminum cap bonding pad region. The Copper Metal Lift failure was also observed for FSG (fluorine-doped silicon glass) -Copper wafer technology. Copper Metal Lift failure is defined as the delaminated interface found between FSG and the barrier layer (e.g. Ta). The delamination interfaces for both Aluminum Cap Lift and Copper Metal Lift failures have been determined with several failure analysis techniques. Some of these techniques are standard FA tools such as TEM (Transmission Electron Microscope) and Auger depth profiling, and some are more special, e.g. nano-indentation. Root cause for each failure mode and its corresponding corrective actions will both be disclosed in this paper. Moreover, the Tilted Metal Lift failure was also observed during wire pull test as ball bond diameter reduced for fine pitch wirebonding. Its root cause will be disclosed too.