Dry-Type off-Gas Treatment Technology of Exhaust Gases From the Semiconductor Industry for Fluorine Recycling

A dry-type off-gas treatment process for recycling fluorine from perfluoro compounds present in off-gases from the semiconductor industry has been developed. This treatment process consists of an electric thermal furnace for the decomposition of perfluoro compounds, a filter, and a fixation furnace for the adsorption of fluorine compounds. In the thermal decomposition furnace, the NF₃ and SiH₄ released from the chemical vapor deposition (CVD)chamber during the etching or cleaning processes are decomposed to HF, SO₂, and SiF₄ in the presence of water vapor. Next, the filter recovers SiO₂ powder from the exhaust gas released from the decomposition furnace. Finally, in the fixation furnace, two types of granular solid adsorbents—calcium carbonate and a sodium compound—adsorb the HF and SiF₄ present in the off-gas, and the gases are recovered as calcium fluoride and sodium fluorosilicate, respectively, for recycling. This paper describes the fluorine compound adsorption properties of both the solid adsorbents—calcium carbonate and the sodium compound—for the optimal design of the fixation furnace. An analysis of the gas-solid reaction rate was performed using the experimental results of the breakthrough curve for each solid adsorbent, and the reaction rate constants and adsorption capacity were obtained for achieving an optimal process design.