The first paper, by Kishimura et al. and published by SPIE in 2002, studied fluorine-containing polymers etched in Cl2-based plasma. A negative NF was added in the equation (5) to get a better fit for their data [8]. Because Cl2 is a reducing gas, the halogen atoms in the polymer should be the fast-etch material. The number of fluorine atoms, NF, in the etch equation should be negative