Surface stoichiometry, structure, and chemisorption on silicon nitride studied by direct recoiling, x-ray photoelectron spectroscopy, and Auger electron spectroscopy

Abstract

The surface stoichiometry, structure, and chemisorption of O2 and H2O have been investigated for surfaces of silicon nitride prepared by (i) chemical vapor deposition (CVD) and (ii) low-energy N+2 ion nitridation of a Si(100) crystal. The technique of time-of-flight (TOF) analysis of directly recoiled (DR) particles combined with x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Ar+ depth profiling have been used for characterization. The results show that CVD Si3N4 is terminated in a silicon rich layer upon which a one monolayer oxide is formed from O2 exposure. The initial O2 chemisorption rate is fast and saturation occurs at 15 L exposure, with the kinetics fitting a one-site model for which the modified sticking coeffient is S/Nf=3.5×10−16 cm2/atom. Chemisorption of H2O produces a surface H:O ratio of 1:1 as determined by DR. Nitridation of a Si(100) surface by low-energy N+2 produces a thin nitride film with XPS binding energies identical to those of CVD Si3N4. Depth profiling indicates nitride film thicknesses of 3 and 8 Å for 0.5- and 3.0-keV N+2 ion bombardment, respectively, in agreement with ion ranges estimated from LSS theory. Defect controlled incorporation of oxygen and carbon during N+2 bombardment is observed.