Recovery of perfluoroethane from chemical vapor deposition operations in the semiconductor industry

Perfluorocarbons, particularly perfluoroethane (C₂F₆), are widely used in the semiconductor industry for plasma cleaning of chemical vapor deposition (CVD) chambers. Although the quantity of C₂F₆ released into the atmosphere by these operations is relatively small, C₂F₆ is a very powerful greenhouse gas, and methods of reducing atmospheric emissions are being sought. One method is to use a selective membrane to concentrate the C₂F₆ so that the gas can be condensed on cooling and recovered as a liquid. In the past, similar membrane vapor separation processes used rubbery polymer membranes that permeate the vapor. However, perfluorocarbon vapors have unusually low permeabilities even in rubbery polymers, because of their large size and low solubility. Therefore, glassy polymeric composite membranes were developed to separate and recover C₂F₆ from CVD chamber exhaust gas. These membranes permeate oxygen and nitrogen, and retain the perfluorocarbon vapor. Membranes with nitrogen/C₂F₆ selectivities of up to several hundred were made from a number of polymers. A process using these membranes to recover 99% C₂F₆ from CVD exhaust gas was designed.