Linear prediction for filtering of data during in-situ monitoring of polishing

#This disclosure relates to using applying a filter to data acquired by an in-situ monitoring system to control polishing.

#An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, 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 metallic 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 or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. An abrasive polishing slurry 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.

#FIG. 2 is a graph comparing filtered platen torque signals generated by a customized filter and a standard low pass filter.

#FIG. 3 is a graph comparing filtered platen torque signals generated by a customized filter and a standard low pass filter.

#Like reference symbols in the various drawings indicate like elements.

#In some semiconductor chip fabrication processes an overlying layer, e.g., silicon oxide or polysilicon, is polished until an underlying layer, e.g., a dielectric, such as silicon oxide, silicon nitride or a high-K dielectric, is exposed. For some applications, it may be possible to optically detect the exposure of the underlying layer. For some applications, the underlying layer has a different coefficient of friction against the polishing layer than the overlying layer. As a result, when the underlying layer is exposed, the torque required by a motor to cause the platen or carrier head to rotate at a specified rotation rate changes. The polishing endpoint can be determined by detecting this change in motor torque.

#FIG. 1 illustrates an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable disk-shaped platen 120 on which a polishing pad 110 is situated. The polishing pad 110 can be a two-layer polishing pad with an outer polishing layer 112 and a softer backing layer 114. The platen is operable to rotate about an axis 125. For example, a motor 121, e.g., a DC induction motor, can turn a drive shaft 124 to rotate the platen 120.