Removal of C2F6 from a semiconductor process flue gas by a ferroelectric packed-bed barrier discharge reactor with an adsorber

The abatement of greenhouse gases from semiconductor processes is becoming important. Methane and/or nitrous oxide are continuously exhausted from the processes, and high concentrations of per-fluorocarbons (PFCs), such as NF₃, C₂F₆ , SF₆, and CF₄, are exhausted during wafer etching and clean up of PECVD (plasma enhanced chemical vapor deposition) chambers. The removal of C₂F₆ from a simulated semiconductor-process flue gas was studied using a hybrid control system, consisting of a ferroelectric packed-bed barrier discharge reactor and an adsorber. The barrier discharge reactor was composed of BaTiO₃ ferroelectric pellets and was operated with AC voltages at 60 Hz. The adsorber was either artificial zeolite or activated carbon. Simulated flue gases consisted of N₂ or N ₂-H₂O mixtures with 1000 to 3000 ppm C₂F₆. The experiments showed: (1) the removal efficiency for C₂F₆ increases with increasing applied voltage until the threshold for spark formation is reached; (2) the removal efficiency increases at lower temperatures and by use of the hybrid system, and decreases with increasing gas flow rate; (3) humidity significantly reduces the reactor´s efficiency as a result of the energy drawn from the discharge for H₂O molecule dissociation; (4) trace CF₄, CO, NO₂, N₂O, and SiF₄ are by-products of the control system; and (5) about 13.5 g of C ₂F₆ is decomposed by 1 kWh of input electrical power to the hybrid system. CF₄ is a by-product from C₂ F₆ removal, while the other by-products come from etching the reactor´s glass wall (SiO₂) by fluorine released from C₂F₆ removal