MASS AND ENERGY ANALYSIS OF GASEOUS SPECIES IN NF3 PLASMA DURING SILICON REACTIVE ION ETCHING

Neutral molecules and positive ions, extracted directly from the react ion zone during reactive ion etching of silicon in NF3 plasma, have be en identified by quadrupole mass spectrometry. The main etching end pr oducts are SiF4 molecules and SiF3+ ions. Reactive species that contri bute to the etching are atomic F radicals and F2+ molecular ions. Most of the positive ions in the plasma hold NF2+ ions and this facilitate s etching of negatively biased Si by bombardment. Likewise, the kineti c energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain r ange of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3 p ressure 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.