Inline refractive index RI measurements have been field proven in balancing cost, speed and measurement accuracy of CMP (Chemical Mechanical Planarization) slurry density and
addition of H2O2 concentration in Slurry Delivery Systems. Especially colloidal silicabased slurries like copper, tungsten and ILD oxide slurries are known to achieve, and remain within a reasonable time, a well dispersed mix throughout the entire fab slurry delivery loop. Ceria based slurries on the other hand have required attention in maintaining a homogenous mix due to their nature of faster settling solids. A traditional circulating flow path was proven by the inline refractive index sensor to show both unstable over time and differing outgoing and returning Ceria slurry densities in the slurry supply loop. Slurry density again is thought to have an impact on polishing removal rate.

The solution was presented by adopting a set of process and integration design rules through a pump-tank-mixer PTM system, where the pump is simultaneously pushing fluid back to the tank working as a mixer and moving fluid to the supply loop. The density measurement was proven to be both stable and same for outgoing and returning Ceria slurry. Another key design in the inline refractometer itself was a proprietary full-bore flow path to allow for the most optimal fluid flow rate at the optical measurement window. The KxS refractive index monitor provided a stable slurry density measurement over five months without maintenance. The smallest detectable RI measurement change was determined to +/-0.05%wt Ceria in the mix.