Optimizing Wafer Polishing: Innovations in CMP Slurry Characterization and Filtration

Contamination control during chemical mechanical polishing (CMP) is critical to achieving high wafer yields and consistent device performance. In our latest CMP slurry study, we set out to address the persistent challenge of particle-induced scratch defects in CMP by combining advanced slurry characterization with innovative filtration technologies.[1]

We began by examining the behavior of a 3 wt% silica slurry under accelerated aging conditions. Through pre-cycling tests, we monitored conductivity, temperature, and pH to characterize how the slurry evolves over time. While pH remained stable, conductivity increased with temperature. This is an important indicator of slurry aging and its potential impact on polishing performance.

With this foundational understanding, we designed a comprehensive DOE (Design of Experiments) to evaluate the effectiveness of our NMB (nano meltblown) filters. These filters were tested across various filter pore sizes to determine their ability to retain particles and reduce surface defects. Using the Entegris AccuSizer® A9000 FX Nano AD system, we measured LPC (large particle count) across multiple size ranges, while defect analysis was performed using the KLA-Tencor Surfscan® SP7 and AMAT G7 SEM.[1]

The results were clear. Our NMB filters demonstrated exceptional retention capabilities—up to 95% for particles larger than 0.43 µm. This high retention directly correlated with a significant reduction in scratch defects, particularly for particles around 50 nm. In fact, total scratch defects dropped to less than 10%, a major improvement in surface quality. While smaller particles (40 nm) showed minimal change, our filtration system proved highly effective against the larger contaminants most responsible for visible damage.

The synergy between our characterization work and filtration strategy created new insight. By understanding how the slurry aged and behaved under different conditions, we were able to tailor our filtration approach to maintain slurry cleanliness throughout the CMP process. Our dual-stage solution combines bulk and point-of-use filtration to ensure consistent LPC control and defect mitigation.

Ultimately, this study reinforces our belief that when advanced filtration is guided by deep process insight it can stabilize the CMP process and improve wafer yield. In addition, we have carried out focused research efforts to enhance filtration efficiency for fine particles (<30 nm), with the objective of reducing underlayer defects and minimizing other subtle surface scratches.

Read the full paper to uncover the science behind our approach and connect with Entegris experts to see how we can help you eliminate both large and fine particle-related scratches and defects. Together, we can unlock greater process stability, higher wafer yield, and long-term CMP process success.

[1] Other Entegris studies address FPC (fine particle count) that may lead to underlayer defects. Contact Your Entegris Technical Representative for more details.