Analysis of the XPS and optical reflectivity spectra of the chemically etched Si(111) surfaces

XPS and optical reflectivity (OR) studies were performed for Si (111) surfaces, finally treated by two alternative chemical etching processes : A - aqueous HF etch, B - diluted CP-4 etch - both followed by methanol bath. Surface deoxidation (A) resulted in low reflectivity coefficient, whereas removal of Si surface layer (B) revealed highly intensive OR spectrum. The core level XPS data showed similarity of the surface structure, irrespectively of the etch process. Contrary, comparison of valence band XPS-and OR spectra revealed qualitative correlation between them, indicating dominant influence of the subsurface bulk defects. More insight into Si oxidation was provided by additional angle- resolved XPS measurements. Two components were distinguished in Ols spectra : the main (E(1) = 532eV) and the minor one (E(2)), shifted similar to 1.5 eV to higher binding energies. Their relative intensity was found dependent on air exposure time and a take-off angle. The peaks were assigned to two different oxygen position : 1) O chemisorbed with methoxy group, 2) bridging O atom.