Open Access

Marvin Schmid, Wolfram Kintzel, Volker Bucher

• Gaseous perfluorocarbons (PFCs), commonly used in dry etching processes, are highly climate damaging due to their outstanding global warming potential. This study investigates the feasibility of using optical emission spectrometry (OES) and varying plasma power to control the composition of a plasma containing oxygen (O2) and fluorine compounds etched in-process from a polytetrafluoroethylene (PTFE) precursor, as a step towards a climate friendly, closed system proposed by Kintzel et al. (2023) [3]. The resulting spectra were compared to plasma containing carbon tetrafluoride (CF4) as precursor to analyse the composition and behaviour of the process atmosphere over time and under different power conditions. We found that an increase of plasma power resulted in an increase of intensity in the spectrum associated with fluorine content relative to the intensity of oxygen. On the basis of these findings a closed loop control system using a PTFE precursor was designed as part of a two step process where the reactive fluorine species were generated in one and supplied to a second plasma chamber. While OES signals were used in the first chamber to control plasma power, the spectrum in the second chamber was measured to verify a steady output of reactive fluorine species. All findings support the feasibility of an effective closed loop controlled system with solid precursors, using OES signals and plasma power as in- and output variables, respectively.