Removal of C/sub 2/F/sub 6/ from a semiconductor process flue gas by a ferroelectric packed-bed barrier discharge reactor with an adsorber

Abstract

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 NF/sub 3/, C/sub 2/F/sub 6/, SF/sub 6/, and CF/sub 4/, are exhausted during wafer etching and clean up of PECVD (plasma enhanced chemical vapor deposition) chambers. The removal of C/sub 2/F/sub 6/ 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 BaTiO/sub 3/ 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 N/sub 2/ or N/sub 2/-H/sub 2/O mixtures with 1000 to 3000 ppm C/sub 2/F/sub 6/. The experiments showed: (1) the removal efficiency for C/sub 2/F/sub 6/ 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 H/sub 2/O molecule dissociation; (4) trace CF/sub 4/, CO, NO/sub 2/, N/sub 2/O, and SiF/sub 4/ are by-products of the control system; and (5) about 13.5 g of C/sub 2/F/sub 6/ is decomposed by 1 kWh of input electrical power to the hybrid system. CF/sub 4/ is a by-product from C/sub 2/F/sub 6/ removal, while the other by-products come from etching the reactor's glass wall (SiO/sub 2/) by fluorine released from C/sub 2/F/sub 6/ removal.