Microwave plasma removal of sulphur hexafluoride

Sulphur hexafluoride (SF6) gas is a common pollutant emitted during the plasma etching of thin films and plasma cleaning chemical vapor deposition (CVD) production processes used in the semiconductor industry. In this paper a method using microwave (2.45 GHz frequency) plasmas sustained at atmospheric pressure for the abatement of SF6 is investigated experimentally for various gas mixture constituents and operating conditions, with respect to its ability to decompose SF6 to less harmful molecules. The destruction and removal efficiencies (DRE) of plasma abatement of SF6 at concentrations between 1.7 and 5% in nitrogen in the presence of water vapor were studied as a function of the total gas flow rate and microwave power. Water vapor proved to be an effective source of free radical species that reacts with the radicals and ions resulting from SF6 fragmentation in the plasma and also, it proved to reduce the process by-products. It was measured that ∼25% of the initial SF6 is converted to SO2. Destruction and removal efficiencies of SF6 up to 99.9% have been achieved.