Inclusion of cerium (Ce) oxide particles as an abrasive into chemical mechanical planarization (CMP) slurries has become popular for wafer fabs below the 45nm technology node due to better polishing quality and improved CMP selectivity. Transmission electron microscopy (TEM) has difficulties finding and identifying Ce-oxide residuals due to the limited region of analysis unless dedicated efforts to search for them are employed. This article presents a case study that proved the concept in which physical evidence of Ce-rich particles was directly identified by analytical TEM during a CMP tool qualification in the early stage of 20nm node technology development. This justifies the need to setup in-fab monitoring for trace amounts of CMP residuals in Si-based wafer foundries. The fact that Cr resided right above the Ce-O particle cluster, further proved that the Ce-O particles were from the wafer and not introduced during the sample preparation.

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