Driven for further silicon reduction, wireless applications utilize Copper interconnection and increase metal layer count from three to five layers. More aggressive ESD structures placed under the bond pads offer a significant opportunity for additional die area and cost reduction. Capping Copper bond pads with Aluminum was selected as the primacy approach for probing and wire bonding Copper devices. There exists an integral relationship between probe damage on the bond pads and the subsequent wire-bondability. As the pad geometry gets smaller, the ratio of the area of probe damage to the bond pad size will get proportionally larger, thereby reducing the available Aluminum necessary to form reliable Gold-Aluminum intermetallic coverage. This paper will describe probe and assembly processes developed for a fine pitch three-metal layer Copper interconnect device with ESD structures placed under bond pads. The relationship between probe conditions and wire-bondability were examined. Ball shear, wire rip and corresponding failure modes were evaluated at various readpoints of thermal aging studies to evaluate the integrity of ball bonds onto the metal stack. Reliability assessment was also performed. Based on the investigations studying the relationship among the pad structures, probe and wire bond quality, recommendations were derived to ensure high quality, stable and reliable bonds for fine pitch wire bonding on multi-layer Copper interconnect devices.

The requirement for improved electrical performance and reduced silicon area has driven Copper to replace Aluminum interconnection as silicon technology is scaled beyond 0.25 /spl mu/m. The front-end change, in turn, pushes wirebond pad pitch from above 100 /spl mu/m to 80 /spl mu/m-66 /spl mu/m range. This creates challenges for back-end to probe and wire bond at fine pitch geometry onto a readily oxidized Copper surface. After several re-metallization structures and types of metallurgy were evaluated, capping Copper bond pads with Aluminum was selected as the primary approach for probing and wirebonding Copper devices. Aluminum re-metallization structure offers many advantages that help leverage existing tooling and knowledge in fab, probing and wire bonding processes. This paper will describe probe and wirebond experiments used to select the proper adhesion and diffusion barrier between Copper and Aluminum, and Aluminum thickness that can withstand the mechanical stress during probing and wire bonding. Probe mark depth and the impact of probe marks to the underlying barrier and Copper pad were examined. Ball shear, wire rip and corresponding failure modes, intermetallic coverage and cratering analysis were evaluated at various readpoints of thermal aging study to evaluate the integrity of the re-metallization structure as well as the quality of ball bonds onto the new structure. Contact resistance measurement and reliability assessment were also performed. One re-metallization structure was recommended for Copper High Performance wire bonded devices.

Driven for further silicon reduction, wireless applications utilize copper interconnection and increase metal layer count from three to five layers. More aggressive ESD structures placed under the bond pads offer a significant opportunity for additional die area and cost reduction. Capping copper bond pads with aluminum was selected as the primary approach for probing and wire bonding of copper devices. There is an integral relationship between probe damage on the bond pads and subsequent wire-bondability. As the pad geometry decreases, the ratio of the area of probe damage to the bond pad size becomes proportionally larger, thereby reducing the available aluminum necessary to form reliable gold-aluminum intermetallic coverage. This paper describes probe and assembly processes developed for a fine pitch three-metal layer copper interconnect device with ESD structures placed under the bond pads. The relationship between probe conditions and wire-bondability were examined. Ball shear, wire rip and corresponding failure modes were evaluated at various read points of thermal aging studies to evaluate the integrity of ball bonds to the metal stack. Reliability assessment was also performed. Based on the investigations studying the relationship between the pad structures, probe and wire bond quality, recommendations were derived to ensure high quality, stable and reliable bonds for fine pitch wire bonding on multi-layer copper interconnect devices