Chemical Mechanical Planarization

Chemical Mechanical Planarization (CMP) is a polishing process used to manufacture wafers for the semiconductor industry. It requires the use of a polishing tool and polishing slurry, which is delivered to the wafer surface and may contain large particles/agglomerates (> 1 μ) as a result of shipping/handling issues, drying, and interactions within the slurry distribution systems. These large particles can, in turn, increase the level of defectives (scratches) on the semiconductor wafer surface found after the CMP process has been completed. Through the use of slurry filtration, these large particles are effectively removed either in the recirculation loop or at point-of-use (POU). Loop or recirculation filtration attempts to remove large particles from the slurry as it is recirculated through a distribution loop which delivers the slurry to the tools. For these applications, 0.3 to 5-micron filters are typically used and flow rates of 1 to 3 GPM are recommended. POU filtration attempts to capture large particles at or near the point at which the slurry is dispensed onto the polishing pad. Flow rates for POU applications should not exceed .5 to 2.5 GPM. Both methods of filtration have tradeoffs concerning the volume of slurry that can be filtered before filter failure and the size of the particles that can be filtered.