Imaging by atomic force microscopy of the properties difference of the layers covering the facets created during SIMS analysis

Atomic force microscopy (AFM) is used in tapping mode in order to study the roughness created in the crater bottom during secondary ions mass spectrometry (SIMS) analysis in silicon, using O2+ primary ions without flooding. Previous studies of the chemical composition of the facets created during the analysis have lead to the conclusion that the facets oriented toward the O2+ beam during the ionic bombardment were close to SiO2 in composition, while the facets hidden from the beam were covered with a sub-stoichiometric oxide SiOx (with x < 2). We show that the AFM phase contrast during tapping mode observation of the facets reflects this composition difference, revealing a sharp contrast between the facets. The observed contrast may arise from the different chemical composition of the facets, leading to a different energy dissipation of the tip/sample system over Si and SiO2 due to the different properties of the materials (hardness, adhesion, etc.). As a comparison, an observation of a surface covered with SiO2 and Si (SiO2 deposed with a 90 nm or 4 nm thickness, and partially removed from a Si surface) shows the same kind of contrast.