Document 7MqQJ3o9BKj3k37QvxxrOLYk8

Dear, This comment addresses 1,2,3,3,4,4,5,5-Octafluorocyclopentene (C5F8, CAS-No. 559-40-0). [PFC etching process in the semiconductor manufacturing] The reason why the perfluorocarbons (PFC) gas including C5F8 is necessary in the plasma etching process of semiconductor manufacturing is shown below. Plasma etching is mostly driven by the chemical and physical reactions of the plasma species occurred in the etch chamber with the exposed semiconductor material to be etched. The PFC gas is dissociated into chemically reactive species like ion and radical in the plasma and its species adsorbed and/or bombard on the wafer surface used for semiconductor. Consequently between reactive species and wafer surface layer occurs reaction. There are some different material exposed to wafer surface for instance silicon and silicon oxide layer. Carbon dissociated from PFC gas bonds to oxygen of silicon oxide because of more bond strength rather than Si-O bond. After that, C-O species volatile from wafer surface, and residue Si bonded with F also volatile. This chemical and physical reactions leads to etching. These are the one of the reason why the PFC including C and F is required. Moreover, silicon wafer has normally trench feature to form line, anisotropy etching is required. This is to say that the differentiate etching rate between lateral and horizontal direction. The polymer passivation of the sidewalls formed by PFC gas species prevents the sidewalls from being attacked and therefore prevents laterally etching of the silicon trench sidewalls from occurring. The deposition of an etch resistant passivation polymer layer on the sidewalls uses a PFC chemistry and the various ratio of Carbon : Fluorine is used for etching process recipe by semiconductor manufacturer in confidential. Therefore examples of PFC etching gas includes C4F6 (Cas No. 685-63-2) and C4F8 (CAS No. 115-25-3) etc., but are not limited to 1,2,3,3,4,4,5,5 Octafluorocyclopentene (C5F8, CAS-No. 559-40-0). For reasons below, there are seldom emission of these gases to the atmosphere. The equipment of etcher involves process chamber connected to a vacuum pump to achieve the proper operating pressures and exhausted to abatement system. PFA gases flow from gas cylinder to the etch chamber by in-line mass-flow controllers. It means almost no emission to the environment due to the closed-system. [C5F8 CAS-No. 559-40-0 decomposition scheme in the atmosphere] For reasons detailed below, CAS-No. 559-40-0 in a state of gas estimated to have a GWP of one year is chemically able to degrade to inorganics in the atmosphere as below and should not be considered to be within the scope of the restriction proposal. Ref: Atmospheric and Environmental Research Incorporated. Calculations of Global Warming Potentials and Atmospheric Lifetimes of C5F8