Effects of rare gas dilution for control of dissociation, ionization, and radical density in fluorocarbon ultrahigh-frequency plasmas

The effects of diluting ultrahigh-frequency C_xF_y plasmas with Xe, Ar, and He are studied by optical emission spectroscopy and Langmuir probe measurement. The Ar and He dilutions are found to shift the electron energy distribution function toward higher energies. Ar and Xe also drastically increase the electron density, whereas He does not change the electron density. As a result, Ar dilution increases the ratio of ion density to CF₂ density. It is expected that the Ar dilution changes the balance between the etching and the polymer deposition and significantly affects the SiO₂ etching characteristics. He dilution causes a high degree of dissociation and a large increase in the density of F atoms for C_xF_y gases, in addition to the dilution of CF₂ radical density, because of its high threshold energy for ionization. The Xe dilution drastically increases the n_e while it maintains a lower electron temperature.