COMPARISON OF ETCHING PROCESSES OF SILICON AND GERMANIUM IN SF6-O-2 RADIOFREQUENCY PLASMA

Reactive ion etching of Si and Ge in SF6-O2 is investigated. Etch rate shows that Si etching is selective with respect to Ge in SF6-O2 (O2<50%); the reverse is observed in SF6-O2 (O2>50%). In agreement with the compared evolution of the F and O concentration in the plasma and of the etch product formation rate obtained respectively, by optical emission spectroscopy and mass spectrometry, the x-ray photon spectroscopy surface analysis reveals that the growth of a SiOxFy layer quenches the Si etching whereas the formation of GeOxFy does not inhibit Ge etching. Using a simple model, an experimental surface reactivity is defined and expressed in function of the experimental data. Results suggest a different behavior for sulfur and oxygen on both materials.