Chemical Mechanical Polishing (CMP) Applications

Chemical mechanical polishing (or planarization) is the most popular technique for removing the surface irregularities of silicon wafers. Typical CMP slurries consist of a nano-sized abrasive dispersed in acidic or basic solution. A chemical reaction softens the material during mechanical abrasion. The abrasive particles have a size distribution which directly affects critical metrics including rate of removal and wafer defects. Particle size analysis is therefore a key indicator of CMP slurry performance.

The typical size range of CMP abrasive particles is 50-250 nanometers and several particle sizing techniques are capable of measuring in this range with varying accuracy and precision. The typical oversize aggregate in CMP slurry is 1-10 microns and appears in the ppm range. The particle characterization challenge comes from the combination of accurately sizing the nano-scale particles while also identifying a relative few micron-scale aggregates.

The DT-1201 acoustic spectroscopy system has also found popularity for CMP applications by measuring both particle size and zeta potential without dilution. Measuring at process concentration eliminates the concern that the presence of oversize particles may be exaggerated or hidden through the dilution step. In addition, measuring zeta potential can predict batch stability. If the magnitude of the potential difference decreases below a certain threshold, then particle-particle interactions including aggregation become much more likely. Zeta potential measurements using the electroacoustic method without dilution show better accuracy for concentrated slurries than other methods. The DT-1201 has also proven to be quite sensitive to finding the larger, troublesome particles while in the presence of the smaller, main population.

Download the Application Note AN165 CMP Slurry Measurements using Acoustic Spectroscopy (You need to be logged in).