The Role of F Atoms in the Reactive Sputter Etching of Silicon Dioxide: Langmuir Probe and Optical Actinometry Measurements

ABSTRACTReactive sputter etching of SiO2 in a low-pressure CF4 -O2 plasma has been investigated using a Langmuir probe to determine ion fluxes to the substrate and optical actinometry to monitor the concentration of F atoms, [F]. Etch yields Y, i.e. the number of substrate atoms removed per impinging ion, are obtained vs O2 composition and vs pressure. At constant pressure Y decreases slightly, but [F] increases considerably, with increasing O2 content. On the other hand, at constant O2 composition both Y and [F] increase strongly with increasing pressure. These results suggest that at low [F], relative to the ion flux to the substrate, the dominant etch mechanism is direct reactive ion etching, with the ions themselves as the main reactants, whereas at high [F] the overall etching is ion-enhanced, with F atoms as the main neutral reactants.