Slurry distribution system filtration

Fig. 1. Generalized CMP slurry distribution system with metrology, assay control, and filtration.

Capitanio et al, Defect Reduction During Chemical Mechanical Planarization by Incorporation of Slurry Filtration, Proceedings of SEMICONlWest Contamination in Liquid Chemical Distribution Systems Workshop (July 1998). 

The removal of large particles and agglomerates is the main objective of filtration. Filtration is also used to eliminate any other contaminants that possibly have been introduced by improper slurry handling or have been collected from within the distribution system. The major criterion of filtration is to remove the oversized particles that could be defect causing without altering the slurry performance. Filtration will be further discussed in Chapter 18. 

CMP slurry delivery system employing filtration for LPC eontrol should consider slurry characteristics including—abrasive type(s) and composition, LPC, PSD, wt% solids, viscosity, chemical composition and the distribution system characteristics—specific pump type and the pumping effects on slurry abrasive, pump size and speed, global distribution loop backpressure, slurry usage and replenishment cycles, slurry turnover rate and typical turnovers before consumption, filter ratings for various locations, allowable pressure drop for filters, and the slurry flow and temperature consistency needs. 

Diaphragm pumps. These offer very gentle handling of slurries and are inexpensive and mobile. However, the pulsating flow can cause feeding and distribution problems in some types of filtration systems, e.g., conventional basket centrifuges. They can also interfere with process instrumentation e.g., flowmeters and loadcells. 

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