Effect of mixing CF4 with O2 on electron characteristics of capacitively coupled plasma

Abstract

Effect of mixing CF4 with O2 on electron parameters in capacitively coupled RF plasma was studied. Adding CF4 gas to fixed O2 flow, electron energy probability functions were measured by a Langmuir probe method. As the CF4 gas was added, the decrease in the probability of low energy electrons was observed. The proportion of low energy electrons decreased gradually as the CF4 gas ratio increased, respectively. From electron energy probability functions, electron densities and electron temperatures were calculated. As the CF4 gas ratio increased, electron density decreased and electron temperature increased. Collision cross sections of low energy electrons can explain electron parameter behaviors. By the strong electron attachment of fluorine species which were generated from CF4, low energy electrons depleted by attachment, and the overall electron temperature increased. However, as the elastic collision cross section of CF4 is not different from that of O2, the heating mechanism and physics of high energy electrons did not change.