SURFACE-ANALYSIS OF SI(111) WAFERS USING 2ND-HARMONIC GENERATION

Optical second-harmonic generation is a sensitive tool for investigati ng symmetry and composition of crystalline surfaces. Vicinal silicon ( 111) surfaces are appropriate and technologically important objects to demonstrate the sensitivity of this technique. Slightly misoriented s ilicon (111) surfaces with respect to the precise crystallographic (11 1)-plane display a step structure which generates contributions of two - and fourfold symmetry to the polarization and orientation dependent second-harmonic signal in addition to the expected components with thr ee- and sixfold symmetry. Chemical modifications of the clean surface influence the components of different symmetry in a characteristic way . Thermally grown and native oxide layers of a thickness of 1 nm can b e distinguished. Copper contamination also changes the different secon d-harmonic signal components systematically. An increase of several si gnal components is observed for copper concentrations exceeding 10(11) cm-2. Relative values for the components of the surface-susceptibilit y tensor are derived using a model that takes into account only surfac e contributions to the second-harmonic signal. Thus, information about the surface topology and about bonding properties in the close vicini ty of the surface are obtained from the second-harmonic signals.