A STUDY COMPARING MEASUREMENTS OF ROUGHNESS OF SILICON AND SIO2 SURFACES AND INTERFACES USING SCANNING PROBE MICROSCOPY AND NEUTRON REFLECTIVITY

Ultrahigh vacuum scanning tunnelling microscopy (UHV-STM) and air/liquid atomic force microscopy (AFM) have been used to evaluate the roughness of silicon surfaces after they have been subjected to pre-gate oxide cleaning. The pre-gate oxide cleaning procedure has involved the removal of the 'native oxide' with solutions of buffered HF (BHF) and dilute HF (DHF). The DHF treatment of Si {100} surfaces has been found by UHV-STM to give the smoothest surfaces for pre-gate oxidation in accord with HREELS and IR studies. A comparison of roughness measurement by UHV-STM relative to air/liquid AFM is given to elucidate the relative merits of those techniques which have different spatial resolution. The MOS gate oxide performance is correlated with pre-gate oxide silicon surface roughness. Data published on the Si/SiO2 interface roughness following growth of the gate oxide are inconsistent. A comparative study of interface roughness, determined with the gate oxide present, by neutron reflectivity experiments, and after removal of the gate oxide with DHF, by scanning probe measurements (SPM) is reported. Since the MOS performance may also depend on the SiO2/contact interface roughness, roughness measurements of the SiO2 gate oxide surface obtained using neutron reflectivity are also reported.