COMPARISON OF INITIAL OXIDATION OF SI(111)7X7 WITH OZONE AND OXYGEN INVESTIGATED BY 2ND-HARMONIC GENERATION

Initial oxidation by high purity ozone and molecular oxygen of Si(111) 7x7 was investigated by second harmonic generation (SHG) with a 1.064 mu m Nd:YAG laser. Decrease of second harmonics (SH) intensity to almo st zero after 5 L ozone gas exposure, in spite of the fact that molecu lar oxygen kept SH intensity for the same amount of exposure, indicate d that ozone is inserted into the Si-Si backbond in the subsurface lay ers more effectively than molecular oxygen. In the initial exposure, r ates of rapid decrease in SH intensity for both ozone and oxygen adsor ption were in the same order of magnitude, although O 1s x-ray photoel ectron spectroscopy (XPS) intensity showed high reactivity of ozone. T his is because of a difference in the information depth between SHG an d XPS so that oxygen species in the subsurface layers are not effectiv e in decreasing SH intensity. This indicates that the process of attac king backbonds is underway even with an initial exposure of <5 L. (C) 1997 American Vacuum Society.