Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion forc
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Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms David J. Steina) and Joseph L. Cecchi Department of Chemical and Nuclear Engineering, University of New Mexico, 209 Farris Engineering Center, Albuquerque, New Mexico 87131
Dale L. Hetherington Microelectronics Development Laboratory, Sandia National Laboratories, MS 1084, P.O. Box 5800, Albuquerque, New Mexico 87185-5800 (Received 14 September 1998; accepted 25 May 1999)
We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO3 concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO3 concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP. I. INTRODUCTION
The mechanism(s) of tungsten removal during chemical mechanical polishing (CMP), a critical process in the production of sub-0.5-m integrated circuit devices,1 is not well understood. Tungsten CMP processes are required to have a low rate of defect generation, produce highly planar parts that exhibit minimal dishing and erosion of surface features, and have a high wafer throughput, all at a minimal cost per wafer processed. A fundamental understanding of the tungsten removal mechanism(s) that occur during CMP will allow much more focused and productive investigation into the creation of next-generation CMP process consumables such as slurries and pads. In the present work, we investigate various interactions between the alumina of the polish slurry and the tungsten surface that occur during CMP. Specifically, we use atomic force microscopy (AFM) and transmission electron microscopy (TEM) to investigate the topography and morphology of post-CMP tungsten to look for evidence of physical damage caused by the polishing process. Physical damage would include plow marks due to alumina penetration and transgranular fracture that a)
Present address: Microelectronics Development Laboratory, Sandia National Laboratory MS 1084, P.O. Box 5800, Albuquerque, New Mexico 87185-5800. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 9, Sep 1999
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may be assisted by intergranular chemical attack. We obtained force curves in situ (in solutions that matched the chemistry of CMP slurries), which depict the adhesion or repulsion between the
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