Overpolishing Window

Step Height Reduction Efficiency and Overpolishing Window... 

The tungsten oxide selectivity is vital to achieve a longer overpolishing window. Do you think it is possible to add an additive to the W slurry to protect the oxide surface to enhance the overpolishing window If so, what type of additive would you recommend Keep in mind that this additive should not hinder the W material removal rate. 

Unlike oxide CMP, STI CMP forms a microstructure that requires an effective polishing stop at the nitride layer and minimized dishing on the oxide (for direct STI). The polishing stop can be accomplished by a control of the removal rate selectivity (oxidemitride). The typical additive component for STI ceria slurries is polyanions that form a protective film on the nitride surface in order to minimize the nitride material removal rate and to increase the overpolishing window. 

The exponential increase in the resistivity at narrow linewidths implies that loss of thickness due to dishing in narrow lines would result in a signiflcantly higher increase in line resistance compared to wide lines. This would be a signiflcant challenge for CMP since it is essential to achieve nearly 100% shorts yield while keeping the Rs within specification limits. This would reduce the overpolish margin and narrow the process window. 

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