On Wednesday March 5, 2025, Jeremy Mettler held his final doctor defense in front of more than 30 people! Dr. Mettler’s thesis was titled “On the Development and Application of Etching-Based Fluorine Radical Probes”.

In this PhD thesis, Jeremy investigates the critical role of fluorine chemistry in high aspect ratio silicon etching, a key process in modern semiconductor manufacturing where uniformity, selectivity, and pattern roughness must meet increasingly strict tolerances. Focusing on the discrepancies in fluorine radical reaction rates with silicon, particularly when using SF6, the study introduces an innovative approach to measure fluorine radical densities using spatially resolved radical probes. These probes, featuring thermocouples with reactive tungsten and inert aluminum tips, were tested in the Plasma-Materials Interaction Chamber (PMIC) and a Tokyo Electron (TEL) etcher, demonstrating a linear correlation between probe response and fluorine density in NF3 and SF6 plasmas. Through calibration and kinetic analysis from 100ºC to 700ºC, the probes provided accurate etch rate measurements and revealed spatial fluorine density profiles above the wafer stage, showing that silicon etch rates directly correspond to fluorine radical distribution. Compared to actinometry, which underestimated densities near the wafer center, the probe-based method offered consistent etch probabilities unaffected by fluorine flux variations, providing new insights into silicon etching mechanisms and a valuable tool for studying fluorine radical distributions.

Congratulations to Dr. Jeremy Mettler on his PhD!