Effect of Abrasive Particle Size on Removal Rate and Defectivity

6 EFFECT OF ABRASIVE PARTICLE SIZE ON REMOVAL RATE AND DEFECTIVITY 

In essence, STI CMP and ILD CMP are in a similar category. They are both required to remove certain amount of silicon dioxide film from the wafer surface. They are both dominated by mechanical actions. Therefore, the particle characteristics of the slurry are very important. In general, the material removal rate is proportional to the particle size. In a study reported by Park et al. [35], over a wide range of experimental conditions the oxide removal rate decreased with decreasing abrasive size. As abrasive particles play a significant role in determining the overall removal rate and surface quality, it is important to examine the relative importance of the mean particle size and particle size distribution. 

The mean particle size is typically represented by the so-called D50, which indicates when the cumulative distribution of particles for a particular particle size reaches 50%. The particle size distribution is typically represented by the difference between D50 and D99. The larger the gap between D50 and D99, the greater the particle size distribution. In a representative study by Chandrasekaran et al. [36], the effects of ceria particle size and size distribution on the removal rate of dielectric materials were carefully elucidated. 

The dependence of oxide removal rate on the tail particle size (D99) and mean particle size (D50) are shown in Fig. 13.25a and b, respectively. 

As shown in Fig. 13.25, the oxide rate is almost independent of slurry D99 under all pressure conditions. The rate for slurry with D99 = 0.14 did show a drop in removal rate. This is the result of a change in D50 for the slurry. As shown in Fig. 13.25, the oxide removal rate shows a linear relationship with D50 under various downpressures. The polish rate slope also increases with increasing 

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