Torque-based end point detection methods for chemical mechanical polishing tool which uses ceria-based cmp slurry to polish to protective pad layer

Abstract

A chemical mechanical polishing (CMP) method is disclosed in which a torque-based end-point algorithm is used to determine when polishing should be stopped. The end-point algorithm is applicable to situations where a ceria (CeO) based CMP slurry is used for further polishing, pre-patterned and pre-polished workpieces (e.g., semiconductor wafers) which have a high friction over-layer (e.g., HDP-oxide) and a comparatively, lower friction and underlying layer of sacrificial pads (e.g., silicon nitride pads). A mass production wise, reliable and consistent signature point in the friction versus time waveform of a torque-representing signal is found and used to trigger an empirically specified duration of overpolish. A database may be used to define the overpolish time as a function of one or more relevant parameters.