Plasma abatement of perfluorocompounds in inductively coupled plasma reactors

Abstract

Perfluorinated compounds (PFCs), gases which have large global warming potentials, are widely used in plasma processing for etching and chamber cleaning. Due to underutilization of the feedstock gases or by-product generation, the effluents from plasma tools using these gases typically have large mole fractions of PFCs. The use of plasma burn-boxes located downstream of the plasma chamber has been proposed as a method for abating PFC emissions with the goals of reducing the cost of PFC abatement and avoiding the NOx formation usually found with thermal treatment methods. Results from the two-dimensional Hybrid Plasma Equipment Model have been used to investigate the scaling of plasma abatement of PFCs using plasma burn-boxes. An inductively coupled plasma (ICP) etching chamber is modeled to determine the utilization of the feedstock gases and the generation of by-products. The effluent from the etching chamber is then passed through a plasma burn-box excited by a second ICP source. O2, H2, and H2O are examined as additive gases in the burn-box. We find that C2F6 (or CF4) consumption in the etching reactor increases with increasing ICP power deposition at constant C2F6 (or CF4) mole fraction, and decreasing C2F6 (or CF4) mole fraction or total gas flow rate at constant power. The efficiency of removal of C2F6 (eV/molecule), however, is strongly dependent only on the C2F6 mole fraction and total gas flow rate. All PFCs in the effluent can generally be abated in the burn-box at high power deposition with a sufficiently large flow of additive gases. In general CF4 generation occurs during abatement of C2F6 using O2 as an additive. CF4 is not, however, substantially produced when using H2 or H2O as additives. The efficiency of PFC abatement decreases with increasing power and decreasing additive mole fraction.