Enhancement of the recombination rate of Br atoms by CF4 addition and resist etching in HBr/Cl2/O2 plasmas

Mass spectrometry has been used to study the influence of the plasma chamber walls on the recombination rates of halogen atoms in a high density HBr/Cl2/O2/CF4 plasma used for silicon gate etching. In these plasmas, CF4 addition results in a transition from SiOx to CFx layer deposition on the chamber walls. We show that this is accompanied by an important enhancement of the surface recombination rate of halogen atoms (specially Br), whose gas phase concentration consequently drops. The same phenomenon is observed when photoresist is etched in an HBr/Cl2/O2 plasma resulting in carbon coating of the chamber walls. This demonstrates that the recombination coefficient of Br atoms on organic polymer surfaces is much larger than on SiO2-like surfaces, and that significant consequences on gate etch processes are expected.