Negative Ion Densities and EEDFs in BCl$_{3}$/N$_{2}$ and BCl$_{3}$/SF$_{6}$ CCP Plasmas

Previous work has shown that the addition of N$_{2}$ or SF$_{6}$ to BCl$_{3}$ plasmas results in an enhancement of the etch rate of GaAs. Langmuir probe measurements were performed to further investigate this enhancement. The energy distribution functions revealed an increase in negative ion density as N$_{2}$ or SF$_{6}$ were added to BCl$_{3}$. The negative ion density reaches a maximum near 55{\%} BCl$_{3}$ for N$_{2}$ mixtures and 40{\%} BCl$_{3}$ for SF$_{6}$ mixtures. This increase is most likely due to dissociative attachment. The shape of the electron energy distribution function in BCl$_{3}$/N$_{2}$ mixtures remains relatively unchanged and there is a decrease in the average electron energy with increasing N$_{2}$ percentage. Energy transfer from nitrogen metastables appears to be responsible for the increased dissociation in BCl$_{3}$/N$_{2}$ mixtures. This contrasts with BCl$_{3}$/SF$_{6}$ mixtures in which the electron density rapidly decreases and the average electron energy sharply increases at low SF$_{6}$ percentages, indicating that electron attachment heating is responsible for the enhanced dissociation.