Slurry System Maintenance

Solid accumulation in low-flow sections of a piping system is another common problem. Alumina and ceria abrasive particles will settle due to their density—exactly the same reason they require supply drum or day-tank stirring. Silica abrasive particles, which are normally well suspended, 

One of the manufacturing challenges with a full-system cleanout, is the need to interrupt manufacturing. Some fabs have installed totally redundant delivery systems, including dispense module and piping. Some adopt a scheduled downtime for system maintenance. Most simply refuse to recognize the need until disaster strikes in the form of unscheduled interruption of slurry delivery or dramatic increase in wafer defects. 

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Redundant dispense engines. Redundant dispense engines have become fairly common in both pump- and non-pump-based slurry dispense systems. Since slurry is both chemically and mechanically aggressive, a backup dispense engine enables system maintenance without interruption of supply to the fab. 

The dissolving system was scheduled for maintenance while the rest of the unit continued at full production rates. The chemical process operator was concerned about the available room in the sump as the slurry accumulated during the two- to three-hour outage. The operator drastically increased the slurry flow-rate into the dissolving system for about an hour and a half period before the shutdown. However, he only increased the flow of acid into the system slightly during that time. The basic process is shown in Figure 4—3. 

Design of the Agitation System for Maintenance of a Slurry These condihons are taken ... 

Impeller Size and Speed at a Specified Power Input 293 Effects of the Ratios of Impeller and Tank Diameters 294 Design of the Agitation System for Maintenance of a Slurry 299... 

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