Plasma processing of materials for advanced manufacturing is a key enabler for synthesis of nanoelectronic systems. In mainstream IC manufacturing, plasma processing is routinely used in etch and deposition steps. However, ensuring process repeatability and reproducibility is a major challenge for the IC manufacturing industry. Processing tools are, in general, run in open loop control mode and plasma parameters such as ion flux and radical densities at the substrate surface are sensitive to drift in tool subsystems, changes in wall condition and wafer loading, for example. Disturbances to key plasma parameters may affect process metrics such as etch depth and anisotropy and result in a significant degradation in device yield and performance. Hence, process reproducibility may be improved significantly by effective closed loop control of the plasma process.

 

In this work we present an experimental demonstration of closed loop control of a capacitively coupled Ar/O2 plasma using an optical emission spectrometer and a hairpin resonance probe as sensors. Design of the control algorithm is facilitated by a process model, which has been derived from a physics-based model and validated by taking step responses experimentally. The efficacy of the algorithm is demonstrated by setpoint tracking and disturbance rejection over a range of operating points.