Etching Characteristic of Graphite and Metal Substrates by Hydrocarbon Plasma in Closed Cavity

Plasma can be used to effectively remove coke from a metal surface. The plasma etching conditions of coke and emission spectrum characteristics on the metal surface in a complex structure can be determined in real-time using the flexible optical fiber of an emission spectrometer. In this study, the glow discharge hydrogen plasma etching characteristics of a graphite sheet covering Cu and Fe electrodes were investigated. Methane plasma and a bare Cu electrode without graphite were used to conduct experiments for comparison. The cathode was heavily etched owing to the chemical and physical reactions of abundant H and other active species. Many hydrocarbon particle shells with fuzzy boundaries of multilayer graphite were observed on the ground electrode as black dots with diameters less than 1 micron. The cracking reaction of etching process in the case of hydrogen plasma with graphite electrodes plays a leading role, but polymerization reaction is dominant for the methane plasma with bare Cu electrodes. Significant excitation peaks of the emission spectrum are observed in regions centered at 388 and 776 nm for the etching of carbon-rich electrodes in hydrogen-rich plasma. Different hydrocarbon and metal substrate bonds can exist even under strong etching conditions.