MEASUREMENT AND CONTROL OF SLURRY FILM THICKNESS AND WAFER SURFACE TEMPERATURE IN CMP

摘要

Experimental techniques are developed to measure slurry film thickness and wafer surface temperature in situ on a commercial CMP tool, and applied to pads having various groove patterns. Slurry film thickness is found to be unresponsive to table speed for some grooves and highly responsive for others. A general relationship is discerned by which slurry film thickening begins at a threshold hydrodynamic state defined in terms of groove flow capacity and table speed. The findings define a critical groove capacity, reached as a pad wears, at which removal rate is expected to fall sharply. Wafer surface temperature is measured for the same groove patterns at various combinations of table and carrier speed. Large circular grooves lead to the highest wafer heating rates and the largest center-to-edge temperature maldistribution. Better control of peak temperature and thermal uniformity is observed with experimental grooves designed to regulate slurry film thickness. For the latter, table speeds that would otherwise lead to overheating exceed the critical flow capacity of the grooves and cause the slurry film to thicken, reducing pad-wafer contact and frictional heat release. Total TEOS removal rates are found to track mean wafer temperature but rate profiles do not track temperature profiles, indicating a separate role of slurry temperature in CMP physics.