Real-Time Control System for Improved CMP Pad Profiles
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1249-E02-02
Real-Time Control System for Improved CMP Pad Profiles Gregory E. Menk1, Sivakumar Dhandapani1, Charles C. Garretson1, Shou-Sung Chang1, Christopher Cocca, Jason Fung1, Jun Qian1 and Stan Tsai1 1 Applied Materials, 974 E. Arques Ave., Sunnyvale, CA 94085, U.S.A. ABSTRACT Chemical mechanical planarization (CMP) pads require conditioning to maintain the surfaces yielding optimal performance. However, conditioning not only regenerates the pad surface but also wears away the pad material and slurry transport grooves. Non-optimized conditioning may result in non-uniform pad profiles, limiting the productive lifetimes of pads. A new approach to conditioning uses closed-loop control (CLC) of conditioning sweep to enable uniform groove depth removal across the pad, throughout pad life. A sensor integrated into the conditioning arm enables the pad stack thickness to be monitored in situ and in real time. Feedback from the thickness sensor is used to modify pad conditioner dwell times across the pad surface, correcting for drifts in the pad profile that may arise as the pad and disk age. Pad profile CLC enables uniform reduction in groove depth with continued conditioning, providing longer consumables lifetimes and reduced operating costs. INTRODUCTION Pad conditioning is used extensively in chemical mechanical planarization (CMP) to maintain optimal process performance. On-wafer thin film material removal rates (MRR) deteriorate rapidly without periodic conditioning of the pad surface with an abrasive disk [1]. Appropriate conditioning intervals are also required to maintain acceptable within-wafer nonuniformity (WIWNU) [2] and defectivity throughout the life of a pad or pad set. However, conditioning not only regenerates but also wears away the pad top surface, including grooves used for slurry distribution. The effective lifetime of a pad can be reduced if the grooves are worn away unevenly. Non-optimized conditioning may result in non-uniform pad profiles that limit the productive lifetimes of pads. Pad profile non-uniformity can have a significant impact on tool operating costs due to consumables replacement and subsequent process re-qualification. The pad conditioning sweep schedule is one of the most significant factors affecting pad profile non-uniformity [3]. For a rotary polishing tool, the cross-platen travel of the conditioning disk is typically divided into radial zones. The residence time of the conditioning disk within each zone, or dwell time, can be adjusted to achieve a desired sweep schedule, and linear and sinusoidal sweep profiles are commonly used. Sweep schedule optimization has been investigated as a means to improve pad wear profiles and ultimately pad lifetimes and on-wafer performance. Models designed to predict dwell time profiles for superior within-pad wear profile performance have been tested by measuring the pad stack thickness or groove depth profiles for extensively conditioned pads [4, 5]. Pad thickness profile measurements are not usually performed during polish operations sinc
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