Electropolishing of thin films poses additional challenges in comparison to bulk material polishing. The existence of a resistive anode/electrolyte boundary layer is crucial for achieving polishing. A finite amount of copper is required to be anodically dissolved to create the boundary layer of the appropriate thickness for effective electropolishing of a given hillock. This is a significant consideration in the application of electropolishing for planarization of thin films where the disparity in the topography is significant in proportion to the thickness of the film. Here electropolishing is shown to effectively remove the bulk of electrodeposited copper layers used in ultralarge scale integration (ULSI) metallization schemes without application of mechanical force and to planarize local topography. Efficient polishing can be achieved under galvanostatic conditions (i.e., constant current between the wafer and a counter electrode). Anodic transient studies indicated that the mechanism of formation of the boundary layer (in mass-transport controlled regime) is determined by the diffusive transport of an acceptor species to the anode/electrolyte interface. Effects of changes in current density and rotational speed of wafer on the extent of planarization have been determined. Under optimal galvanostatic and hydrodynamic conditions, the disparity in the topography over wide trenches adjacent to dense features decreased by 60%. © 2002 The Electrochemical Society. All rights reserved.

This investigation studies the effects of the direction of electron flow on the activation energy and current exponent of electromigration failure of copper interconnects using conductors terminated by vias at both ends. The activation energy of a downstream case ͑0.91 eV͒ was found to be similar to that of an upstream case ͑0.86 eV͒, suggesting that failure was primarily caused by diffusion along the Cu/SiN x interface for both cases. Mean time to fail with the upstream flow condition exceeded that with the downstream condition by a factor of ϳ2 at 300°C and 1(10 6 ) A/cm 2 . The current exponent ͑with a link current density in the range of 1ϫ10 6 to ϳ5ϫ10 6 A/cm 2 ) of a 0.22 m via/link structure was determined to be 1.44 and 1.87 with upstream and downstream electron flow, respectively. These differences have been correlated to the locations of void nucleation and their physical size for the two electron flow conditions. Furthermore, increasing the via/link size resulted in a slight increase in the current exponent, consistent with the model proposed by Lloyd ͓J. R. Lloyd, J. Appl. Phys. 69, 7601 ͑1991͒.͔

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The effects of changes in test temperature (Ϫ196 °C to 25 °C) and grain size (40 to 165 mm) on the dynamic cleavage fracture toughness (K ID ) and Charpy impact toughness of polycrystalline niobium (Nb) have been investigated. The ductile-to-brittle transition was found to be affected by both changes in grain size and the severity of stress concentration (i.e., notch vs fatigue-precrack). In addition to conducting impact tests on notched and fatigue-precracked Charpy specimens, extensive fracture surface analyses have been performed in order to determine the location of apparent cleavage nucleation sites and to rationalize the effects of changes in microstructure and experimental variables on fracture toughness. Existing finite element analyses and the stress field distributions ahead of stress concentrators are used to compare the experimental observations with the predictions of various fracture models. The dynamic cleavage fracture toughness, K ID , was shown to be 37 Ϯ 4 MPa and relatively independent of grain size (i.e., 40 to 105 mm) and test temperature over the range Ϫ196 °C to 25 °C.