Initial Stage of Hydrogen Etching of Si Surfaces Investigated by Infrared Reflection Absorption Spectroscopy

Abstract

The initial stage of etching reactions (breaking the Si–Si back bonds) of Si(100) and Si(111) surfaces exposed to hydrogen at room temperature was investigated by buried metal layer-infrared reflection absorption spectroscopy. The peaks of SiH2 scissors and SiH3 deformation modes (<1000 cm-1) were successfully observed as clear indicators of the initial stage of hydrogen etching reactions. On the Si(100) surface, the hydrogen exposure dependence of these peaks indicated that the etching reaction starts in the relatively low-exposure region of ≥300 L (1 L=1×10-6 Torr s). We found that the adjacent dihydride is a precursor to breaking the Si back bonds. On the Si(111) surface, it was found that the adatom's two back bonds are easily broken, and that adatom trihydride is generated at a low H-exposure of 70–500 L. Adding to this dominant reaction, the etching of the rest-atom layer was observed at H-exposures higher than 10000 L.