Particle Size Analysis of CMP Slurries-SPOS versus Fraunhofer

Abstract: The semiconductor industry is moving toward smaller line widths and more layers. One of the most important process considerations that will lead the way to this higher density chip technology is more sophisticated control of the planarization steps. The planerization or polishing steps are effected by the use of colloidally dispersed metal oxide slurries (known as CMPs which stands for Chemical-Mechanical Planerization), primarily silica and alumina, with mean diameters in the 10-200 nm range. These slurries are applied to spinning polishing pads on which rest the wafers. In the past, Laser Diffraction was most commonly used to characterize the particle size distribution of these slurries. It has always been known that these slurries contain a small volume percentage of particles greater than 1 micron in size. It is believed that these particles can cause scratches and other defects in the wafer surfaces. This paper will demonstrate that by virtue of the nature of the measurement, Laser Diffraction is inadequate to the task of quantitatively determining the concentration of out-of-spec slurry particles. On the other hand, Single Particle Optical Sizing or SPOS, because it counts particles, will be shown to be an excellent tool for characterizing CMP slurries.