Mass and energy analysis of gaseous species in NF3 plasma during silicon reactive ion etching

Abstract

Neutral molecules and positive ions, extracted directly from the reaction zone during reactive ion etching of silicon in NF3 plasma, have been identified by quadrupole mass spectrometry. The main etching end products are SiF4 molecules and SiF+3 ions. Reactive species that contribute to the etching are atomic F radicals and F+2 molecular ions. Most of the positive ions in the plasma hold NF+2 ions and this facilitates etching of negatively biased Si by bombardment. Likewise, the kinetic energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain range of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3 pressure of 6.7 Pa, the characteristic mean ion energy of 4 eV at an rf power of 10 W increases to 20 eV by increasing the rf power to 90 W.