Electron energy distribution function of capacitive coupled electronegative plasma: The role of flow rate of electronegative gas in Ar

The advantages of negative-ion assisted etching and charge -free ion implantation in semiconductor manufacturing has prompted investigations into electronegative plasmas. We have presented here the measurement results of 40.68 MHz-driven capacitively coupled Ar plasma mixed with electronegative gas by using Langmuir electrostatic probe. Three kinds of electronegative gases (O₂, Cl₂ and SF₆) into Ar plasma were considered. We found that the electron energy distribution of Ar plasma exhibits a typical bi-Maxwellian distribution at the low pressure of 2.0 Pa like other author´s re port. As adding electronegative gas into Ar plasma, there appeared a high-energy peak in the electron energy distribution function (EEDF). While the flow rate of the electronegative gas into Ar plasma was increased, the high-energy peak in EEDF shifted toward a higher energy due to bulk heating, meanwhile, the electron density reduced significantly, especially for the strong electro-negative SF₆/Ar plasma, the electron temperature increased. The negative ion characteristics are closely related to the changes in the EEDF, electron temperature and density. We calculated the electronegativity of Ar plasmas with three kinds of electro-negative gases. In general, comparison of these characteristics for different electronegative gases provides useful information for deeper understanding of electronegative plasmas.