Effects of substrate cooling on the ion density in oxygen inductive discharge

In oxygen inductive discharge, the ion density decreases as wafer temperature decreases by substrate cooling. The ion density, electron temperature and wafer temperature were measured simultaneously at the substrate position. When the substrate is cooled down, the ion density is decreased whereas it is increased during heating by plasma. This is because the neutral species in the plasma are cooled due to substrate cooling and decrease of wafer temperature. Gas cooling in oxygen plasma, which represents lower gas temperature, accelerate the recombination probability, causing ion density to reduce. The ion density and electron temperature at the substrate position are obtained by a wafer-type two-dimensional (2D) probe using the floating harmonics method (FHM). Electron energy probability functions (EEPFs) were measured at the center position which show similar correlations between wafer temperature and plasma density. Furthermore, effects of substrate cooling in Ar/O2 plasma are measured.