Spatially Resolved Endpoint Detection of Silicon Dioxide Etching in CF₄/O₂/Ar Plasma via Multi-Channel Optical Emission Spectroscopy

The etching uniformity was monitored from a spatially resolved endpoint detection signals using multi-channel optical emission spectroscopy (OES) based on plasma emission spectral analysis. Endpoint signals were detected in eight spatially separated regions of plasma during silicon dioxide (SiO₂) etching in CF₄ / O₂ /Ar plasma. Strong spatial resolution of the endpoint was observed at wavelengths of 307–314 nm (CO 3^rd positive: b³Σ⁺, v′=1 → a³Π, v″=3 or b³Σ⁺, v′=0 → a³Π, v″=2), 428–434 nm(CO triplet: d³Δ, v′=16 → a³Π, v″=3 or d³Δ, v′=14 → a³Π, v″=2) , most argon wavelength(772.4nm, 811.5nm,…) and no resolution at other wavelengths. All of these wavelengths originate from radiative transitions from high-energy states to metastable states. The 307~314 nm and 428~434 nm ranges are related to byproduct of oxide etching, and argon wavelengths such as 811.5 nm are not. Spatially resolved endpoint signals at byproduct-related wavelengths showed high correlation with the oxide exposure moment at each etching point. Argon-related signals exhibited spatial variations, but correlation with oxide exposure was unclear. These results indicate that endpoint resolution was observed only at wavelengths sensitive to changes in metastable state density, and that etch uniformity can be effectively monitored using etch product-related wavelengths among the spatially resolved endpoint signals.