Endpoint control of multiple substrate zones of varying thickness in chemical mechanical polishing

#The present disclosure relates generally to monitoring of multiple substrates during chemical mechanical polishing.

#An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semi conductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non planar surface. In addition, planarization of the substrate surface is usually required for photolithography.

#Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad with a durable roughened surface. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as a slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

#FIG. 1 illustrates a schematic cross-sectional view of an example of a polishing apparatus having two polishing heads.

#FIG. 2 illustrates a schematic top view of a substrate having multiple zones.

#FIG. 3A illustrates a top view of a polishing pad and shows locations where in-situ measurements are taken on a first substrate.

#Like reference numbers and designations in the various drawings indicate like elements.

#Where multiple substrates are being polished simultaneously, e.g., on the same polishing pad, polishing rate variations between the substrates can lead to the substrates reaching their target thickness at different times. On the one hand, if polishing is halted simultaneously for the substrates, then some will not be at the desired thickness. On the other hand, if polishing for the substrates is stopped at different times, then some substrates may have defects and the polishing apparatus is operating at lower throughput.

#In some cases, the initial thicknesses of two substrates on a same platen can be different. In such cases, starting the polishing operation on both substrates simultaneously with substantially same polishing rates may lead to the thinner substrate reaching the polishing end point sooner than the thicker substrate. However, since it is desirable to rinse the substrates simultaneously and as soon as the polishing end points are reached, it could be of interest to adjust the polishing process such that the end points for both substrates are reached together or at least within short time from each other. By determining a time offset for starting the polishing operations of the two substrates the substrates can be made to achieve closer endpoint conditions. By “closer endpoint conditions,” it is meant that the substrates would reach their target thickness closer to the same time than without the time offset, or if the substrates halt polishing at the same time, that the substrates would have closer to the same thickness than without the time offset.