In-situ CMP copper endpoint control system

Describes the design, operation, and algorithms for an in-situ CMP endpoint detection and control system, with particular emphasis on copper polishing. The system's eddy current-based sensor gives absolute surface metal thickness. Its multi-angle reflectometer gives eight optical reflectance measurements. The endpointer improves on existing sensors and techniques in several ways. It can process reflectance traces individually according to their endpoint sensitivity, which applies to dielectric polishing and copper barrier removal processes. Also, it merges reflectance signals for higher signal-to-noise ratios, which benefits copper CMP. Finally, the system can fuse the reflectance data with thickness readings for more robust endpoint detection.