Plasma etch is a semiconductor manufacturing process during which material is removed from the surface
of semiconducting wafers, typically made of silicon, using gases in plasma form. A host of chemical
and electrical complexities make the etch process notoriously difficult to model and troublesome to
control. This work demonstrates the use of a real-time model predictive control scheme to control plasma
electron density and plasma etch rate in the presence of disturbances to the ground path of the chamber.
Virtual metrology (VM) models, using plasma impedance measurements, are used to estimate the plasma
electron density and plasma etch rate in real time for control, eliminating the requirement for invasive
measurements. The virtual metrology and control schemes exhibit fast set-point tracking and disturbance
rejection capabilities. Etch rate can be controlled to within 1% of the desired value. Such control represents
a significant improvement over open-loop operation of etch tools, where variances in etch rate of up to
5% can be observed during production processes due to disturbances in tool state and material properties
