Etch Process Control

Endpoint Detection

Endpoint detection determines exactly when to stop etching — critical for removing the target film without over-etching into the layer below.

Common endpoint methods:

• Optical Emission Spectroscopy (OES): Monitors the light emitted by plasma species. When the target film is fully etched through, the chemical composition of the plasma changes, altering emission wavelengths. For example, when SiO₂ is cleared, CO emission drops and Si emission appears.
• Interferometry: A laser beam reflects off the film being etched. As thickness decreases, interference fringes are observed. Counting fringes gives real-time thickness information.
• Mass spectrometry: Monitors volatile etch byproducts in the exhaust. Composition changes signal endpoint.

Uniformity and Process Monitoring

Etch uniformity — consistent etch rate across the wafer — is managed through:

• Multi-zone gas distribution: Center and edge gas injection ratios are tuned to compensate for radial flow patterns.
• Multi-zone RF bias: Different RF power to inner and outer zones of the electrostatic chuck.
• Temperature control: Multi-zone ESC (Electrostatic Chuck) with independent heating zones for center, middle, and edge.
• Process kit design: Focus rings, edge rings, and confinement rings shape the plasma to improve uniformity.

Etch tools generate rich FDC (Fault Detection and Classification) data: chamber pressure, RF parameters, temperatures, gas flows, and OES spectra — all sampled at high rates during each etch step.