platen

The platen in a CMP (Chemical Mechanical Planarization) tool is the large rotating table or platform on which the polishing pad is mounted, providing the mechanical foundation for the planarization process. The platen rotates at controlled speeds typically ranging from 30 to 120 RPM, with its rotational speed directly affecting the relative velocity between the wafer and pad — a key parameter in the Preston equation governing removal rate. Modern CMP tools use multiple platens (commonly three) in a sequential configuration, enabling multi-step polishing processes without wafer unloading: for example, in copper CMP, the first platen performs bulk copper removal at high rate, the second platen clears the barrier layer with different selectivity, and the third platen performs a buff or touch-up polish for surface finishing and defect reduction. Platens are precision-machined from stainless steel, aluminum, or granite composite materials and must maintain exceptional flatness (typically within ±25 μm across the full diameter) to ensure uniform pressure distribution across the wafer. Internal cooling channels circulate temperature-controlled fluid (typically deionized water or coolant) to manage the heat generated by friction during polishing — slurry chemistry, removal rate, and pad properties are all temperature-sensitive, so platen temperature control within ±0.5°C is critical for process stability. The polishing pad is adhered to the platen surface using pressure-sensitive adhesive (PSA), and pad replacement during maintenance must ensure uniform adhesion without trapped air bubbles that would create pressure non-uniformities. Platen assemblies include integrated slurry delivery systems with dispense arms that distribute slurry across the pad surface, pad conditioning systems, and rinse capabilities. Endpoint detection systems are often embedded in the platen — optical sensors (for reflectivity-based endpoint) or eddy current sensors (for conductive film thickness monitoring) are mounted in the platen surface and measure through windows in the polishing pad as the wafer rotates over the sensor position, providing real-time information for process control and automatic endpoint determination.