Requirement for High Selectivity Slurry

The key ingredients to a successful STI process are the achievement of well-dispersed abrasive ceramic particles having high oxide-to-nitride selectivity and producing few microscratches on the wafer. Silica slurry had been conventionally used in the STI CMP process, however, ceria (Ce02) slurry with high oxide-to-nitride selectivity has been introduced as the thickness of silicon nitride film is decreased by design rule restrictions. 

FIGURE 3.2 (See color insert) The effect of overpolishing on the characteristics of the device (top) the decrease of gate length by overpolishing (bottom) the shift of threshold voltage in the device. 

If the effective gate length (L ff) decreases, subthreshold drain current (Ip) may increase as shown by  

2 Particle Engineering of Ceria Nanoparticles and Their Influence on CMP Performance 

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