Defect-causing large particle

The cumulative LPC is a more sensitive measure of the defect-causing large-particle growth than the PSD measurement. Such large particles could cause scratches on the wafers and issues with the tighter retention of the slurry,... 

An oxide scratch is the most commonly seen defect after oxide CMP. The scratches on the oxide surface are mostly due to a very small amount of large particles in the slurry. As a typical oxide CMP slurry may contain as much as 10 % by weight of abrasives, there are ample opportunities for defect-causing oversized particles to reach a wafer surface. As shown in Fig. 17.1, some of the scratches are large enough to be seen under a regular optical microscope. Others may require an electron microscope. 

Another practical difficulty in characterizing the correlation between slurry properties and defect level is that the absolute number of these oversized particles is very less in relation to the overall number of particles in the slurry. As shown in Fig. 13.29, the number of large particles that is capable of causing defects is in the range of 2.0 x 10 to 9.0 x 10. A typical slurry with mean size of 130 nm has an average of 1.1x10 oversize particles >0.5 pm and 2.3 X 10 total abrasive particles. 

The removal of large particles and agglomerates is the main objective of filtration. Filtration is also used to eliminate any other contaminants that possibly have been introduced by improper slurry handling or have been collected from within the distribution system. The major criterion of filtration is to remove the oversized particles that could be defect causing without altering the slurry performance. Filtration will be further discussed in Chapter 18. 

Mechanical activation of mixtures involves the dispersion of solids and their plastic deformation. These processes cause the generation of defects in solids they also accelerate the migration of defects in the bulk, increase the number of contacts between particles, and renew the contacts. All these factors provide chemical interaction between solids initiated by mechanical loading. These factors are the subject of investigations in one of the fields of solid state chemistry, namely, the mechanochemistry of inorganic substances, which is intensively developed. In particular, a large... 

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