CHARACTERIZATION OF BCl₃, SF₆, and BCl₃/SF₆ PLASMAS USING LANGMUIR PROBE MEASUREMENTS

Abstract

A Langmuir probe study in BCl3, SF6, and mixtures of BCl3/SF6 capacitively-coupled plasmas is presented. In this study, energy distribution functions, electron temperatures (and average electron energy) and electron, positive ion, and negative ion densities were determined as a function of process conditions such as RF power, chamber pressure, and SF6 percentage in the total flow. With the addition of only 10% SF6 to the BCl3 plasma, the electron density rapidly halved to 5.7 x 108 cm-3, and the electron temperature sharply increased to ~4.3 eV (~1.1 eV increase). This is characteristic of electron attachment heating, whereby low energy electrons attach to species within the plasma, and the average energy of the fewer remaining electrons must increase in order to sustain the same power dissipation. These results confirm that the increased dissociation and enhancement in GaAs etch rate with SF6 added to BCl3 plasmas was due to electron attachment heating.