| 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.;It has been previous observed that the etch rate of GaAs increased when SF6 was added to BCl3 plasmas, and that this increase was due to increased dissociation of BCl3 and subsequent increases in Cl and Cl2 densities, along with a possible reduction in recombination of reactive etching species via formation of BClF and BCl2F. It was hypothesized that this effect was primarily due to an increase in electron temperature (or average electron energy) as a result of electron attachment heating with the addition of SF6.;In a pure BCl3 plasma at 50 mTorr and 150 W power the electron density was determined to be approximately 1.1 x 109 cm -3 and the electron temperature was near 3.2 eV. Under the same conditions in a pure SF6 plasma, the electron density was 4.1 x 10 8 cm-3 and the electron temperature was 5.5 eV. With the addition of only 10% SF6 to the BCl3 plasma, the electron density rapidly decreased to 5.7 x 108 cm-3 , and the electron temperature sharply increased to about 4.3 eV (a ∼1.1 eV increase). This is characteristic of electron attachment heating, whereby low energy electrons attach to species within the plasma, and the average electron temperature of the fewer remaining electrons must increase in order to sustain the same power dissipation. These results therefore confirm that the increased dissociation and enhancement in GaAs etch rate with the addition of SF6 to BCl3 plasmas was due to electron attachment heating. |
