Slurry blending

In the wet process the clay minerals are crushed and slurried with water to allow pebbles and other rock particles to settle out. The limestone is also crushed and slurried. Both materials are stored in separate bins and analyzed. Once the desired ultimate composition is determined, the slurry blend is ground and then partially dried out. 

Figures 18.1-18.4 present the distributions of pH, conductivity (pS/cm), ORP (mV), TDS (ppm), density (g/cc), and wt% solids in SS-25, W2000, and EP-C5001 slurry blends. These bench-top blending and measurement...

Monitoring and control of CMP slurry properties is essential for effective and uniform CMP processes. Bench-top blend sensitivity analysis helps in identification of the most sensitive blend monitoring and control parameter. Two- and three-component blends of CMP slurries can be created and monitored based on the measurements of density, wt% solids, refractive index, pH, and oxidizer level. Typical silica oxide slurry blend ratio is controlled using density as a control parameter, whereas tungsten and copper CMP slurries usually need an autotitrator for periodic monitoring of the oxidizer level. 

TABLE 18.2 Required Minimum Flow Velocity (RMFV) of Slurry Blend in the Global Loop, Abrasive Settling Rate (SR), and Stokes Number (St) for Tested CMP Slurries. SR Values Depend on Selected Transmission and Back-Scattering Zones. (A) = Slurry Abrasive Component Only and (B) = Slurry Blend. 

Such systems may provide dynamic control of slurry blend ratio and integrated slurry metrology. POU blending is most suitable for limited pot-life slurry blends and can provide consistent blend over time, but may have limitations in metrology and advance warning on slurry health changes. 

Roberts BR, Singh RK, Pierce A, Blachier O. Slurry quality and consistency in a continuous slurry blending and distribution system. Proceedings of the 16th International VMIC. 1999.p 495-500. 

Schematic diagrams for the synthesis of BC-based composites (a) biosynthesis, (b) impregnation, [c] slurry blending, and (d) solution blending.

Figure 14.3 SEM images of BC-alginate films prepared by biosynthesis (a], by slurry blending (b], and by solution blending (c).

In practice, CMP slurry blending and delivery systems can be periodically monitored for zeta potential in an effort to detect trends and changes that could affect CMP slurry hdelity. As an example, Figure 12.17 shows a transient zeta potential measurement for a typical slurry where a decreasing zeta potential trend towards a more unstable regime was detected the process engineer at this point may elect to troubleshoot the system proactively and/or conduct other measurements (e.g., PSD) for agglomeration detection. 

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