Novel Method of Separating Probe and Wire Bond Regions Without Increasing Die Size

摘要

The drive for enhanced electrical performance and reduced silicon area has triggered significant changes 'in wafer fabrication, wafer level testing, and packaging technologies. In the wafer fab, copper is quickly replacing aluminum as the interconnect metal of choice for technologies 0.13μm and below. To overcome the difficulty of wire bonding onto readily oxidized copper bond pads, capping copper bond pads with aluminum has been the industry standard remetalization for wire bonding for copper technology. In terms of wafer level testing and packaging, the resulting fine pitch geometry has created challenges for both cantilever probe and wire bond processes. Pad damage due to probe marks has been shown to cause "non-sticks" and "lifted bonds" at wire bonding. The wire bond yield loss due to pad damage is aggravated for fine pitch since increasingly smaller bonded ball diameters are formed on top of the same damage area caused by the probe mark. Wire Bond parameter optimization can minimize wire bond yield loss but cannot eliminate the problem. One logical solution is to lengthen the bond pad to create separate regions for probing and wire bonding. However, this method can result in a larger die size. This paper will reveal a unique bond pad structure that provides separate regions but yet results in no impact to the existing die size. This bond pad structure utilizes the aluminum cap layer to create a longer bond pad without changing the size of the underlying copper last metal, resulting in no impact to the existing die size. Evaluations were conducted on 0.13μm CMOS technology, with cantilever probing and wire bonding on 52μm bond pad size. Failure analysis and test methods to detect failures will be discussed. Designs of experiments for probing and wire bonding processes, characterization studies, and reliability results will be presented.