Slurry Delivery

Although typically not thought of as a platform for more than presenting a flat surface, platens are being exploited in several ways to enhance overall CMP performance. Included in these approaches are temperature control, slurry delivery routing, and pressure control. 

H. Mizuno, Slurry Delivery System Design for Tungsten Chemical Mechanical planarization Manufacturing Site, presented at ISSM, Oct. 10, 1997. 

Commercial suppliers of bulk slurry delivery equipment have taken several different approaches to measuring slurry constituents. In addition, there are different approaches to replenishing a daytank as its slurry is consumed by the polishing process. To further complicate things, measure-... 

One of the ongoing challenges is the fact that most slurry delivery systems are designed and built for final steady-state use at full-scale manufacturing. Unfortunately the needs during startup may be very different from the needs at full buildout. Compromises must be made. There are no firm rules to... 

Redundancy of slurry delivery systems or system components is an emotional and user-specific decision. While all manufacturers strive to make dispense systems and all peripherals as reliable as possible, compromises must be made for cost, space, slurry lifetime, and manufacturing philosophy. In the end, it usually comes down to how much one is willing to pay for 99.99% uptime versus 99% uptime. Some of the common strategies employed include... 

Fig. 5. Valve boxes for global slurry delivery system.

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. 

Thakurta G, Borst CL, Schwendeman DW, Gutmann RJ, Gill WN. Pad porosity, compressibility and slurry delivery effects in chemical-mechanical planarization modeling and experiments. Thin Solid Films 2000 366 181-190. 

FIGURE 18.5 LPC distribution during handling of a 30 wt% solids silica abrasive slurry in a VPDS for slurry delivery (BOC Edwards P2200). 

Present results suggest that most of the silica slurry abrasives can be kept in dispersion by maintaining a RMFV value of 0.5ft/s, whereas alumina and ceria slurries require 1.5 to 2.5ft/s, depending on abrasive and chemical composition of the slurry. Next generation slurry delivery systems should be able to measure and control abrasive particle and chemical characteristics (to ensure mix accuracy and control of time sensitive components such as hydrogen peroxide, ammonium hydroxide, etc.) of the slurry on a real-time basis and consistently provide good slurry at the CMP tools. 

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