COLLISIONAL VERSUS ELECTRONIC SPUTTERING OF SIO2

The SiO2 sputtering yield was determined for 170-300 keV He+ ion bomba rdment. The low sputtering efficiency and blistering at high ion doses make high-energy He+ ion sputtering yields difficult to determine, bu t by modifying a measurement method previously used for heavy ions, th e sputtering yield could be quite accurately determined after sputteri ng only 20 angstrom of SiO2. The sputtering yield was found not to be proportional to the energy deposited by the ion in elastic collisions at the surface of SiO2. Comparison with SiO2 sputtering yields found i n literature shows that the sputtering yield increases with increasing energy deposited in electronic excitations for similar energy deposit ed in elastic collisions, indicating that electronic effects probably have to be included in the description of the sputtering process. Sinc e the electronic effects do not seem to be independent of the sputteri ng by elastic collisions, it is suggested that SiO2 sputtering be cont rolled by a mixed collisional-electronic mechanism. Sputtering yield m easurements were also performed for varying angles of ion incidence an d, here also, good agreement could be achieved with predictions based on a mixed sputtering mechanism.