In-line in situ sensing of OH radicals from a remote plasma source using Faraday rotation spectroscopy

Consistent delivery of radicals to the wafer in a semiconductor processing chamber that is equipped with an upstream remote plasma source (RPS) is critical to device performance and yield of dies on the final product wafer. In situ measurement of these radicals can be a valuable tool to achieve precision processing, minimizing within-wafer, wafer-to-wafer, and chamber-to chamber variations. However, absolute measurement of these radicals is difficult using emission spectroscopy due to dependencies on factors other than the radical concentration such as plasma power and mixture composition. Direct laser absorption spectroscopy of molecular radicals is complicated by interferences by molecules sharing the same molecular bond and similar absorption frequencies. Here, we present a real-time in situ radical-selective monitor of OH using near-infrared Faraday rotation spectroscopy. The developed solution isolates the signal from interference from the OH stretch of H₂O and is placed in-line between the RPS and the chamber. Results from measurements of a remote H₂/O₂/Ar plasma will be discussed.