High-Resolved Diagnostics for Real-Time Pulse Shape Control

Pulsed RF plasmas are essential in high-aspect-ratio contact (HARC) etching for advanced memory devices, as they suppress charge buildup at the bottom of HAR features. Temporal RF modulation mitigates surface charging and ion distortion, improving profile fidelity. However, rapid shifts in plasma impedance between pulse-on and afterglow phases require precise, real-time pulse shape control to maintain stable, uniform processing.

Although modern auto-matching units respond on microsecond timescales, real-time control is constrained by latencies in data acquisition and actuation, typically in the millisecond range. These delays stem mainly from diagnostic bottlenecks: Optical Emission Spectroscopy (OES) has integration delays, and microwave probes with network analyzers are limited by slow sweeps. As a result, fast transients in pulsed plasmas often go undetected and uncorrected.

To address this, we present a passive, high-speed sensing method using two in-house-developed sensors: the Optical Plasma Monitoring Sensor (OPMS, Rainbow Corp.) and the Plasma Sheath Monitoring Sensor (PSMS, Rainbow Corp.). These tools enable non-invasive, microsecond-resolved measurements of DC bias, sheath potential, and time-resolved optical emission. This system offers real-time access to transient plasma dynamics and supports future adaptive waveform and impedance control strategies essential for reliable pulse shape control in next-generation HARC etching.