MICRO: Characterizing CMP

A case study investigates how conditioning CMP pads with different diamond abrasives affects film removal rates, wafer-to-wafer nonuniformity, wafer defects, and pad lifetime. hemical-mechanical polishing (CMP) has enabled the production of advanced semiconductor devices by producing a globally planar wafer surface. The near-atomic-level flatness achieved by CMP is driven by the optical depth of focus issues of photolithography, which is a highly sophisticated process. Photolithography requires a flat surface to image dense multilayer integrated circuits. In general, the smaller the device features, the flatter the substrate must be. At the current device technology node, global wafer planarization and CMP are necessary for building reliable next-generation multilevel interconnects. The CMP process is highly dependent on consumables, such as slurries and polishing pads. This article investigates the impact of polishing pad conditioning on silicon dioxide interlevel dielectric (ILD) and shallow trench isolation (STI) CMP processes. The Role of Pad Conditioning The CMP process requires a polyurethane polishing pad; a slurry composed of abrasive, chemicals, and water; and a wafer carrier. The wafer carrier supports the wafer during CMP and applies the necessary load or pressure to remove material from the wafer surface. In addition, this carrier can rotate during polishing to achieve uniform system kinematics in order to achieve better polishing uniformity. In an orbital CMP tool, slurry is distributed through and onto the moving polishing pad surface. The polishing pad has a significant effect on CMP process performance. It transports the slurry to the pad/wafer interface, has an impact on wafer-polishing nonuniformity, and effects global wafer and device planarity. The condition of the polishing pad surface during CMP is critical for optimum and predictable process performance. Pads such as the IC1000 from Rodel (Newark, DE) consist of a thin porous closed-cell polyurethane material. Because the surface of a new (unconditioned) polishing pad