Effect of probe tip size on atomic force microscopy roughness values for very smooth samples

Two-dimensional geometric models and experimental data are used to evaluate the effect of tip shape artifacts on atomic force microscopy images, roughness values, and power spectra. The effects of tip size are studied as a function of the surface feature height, spacing, and width. The models demonstrate that the need for sharp tips is dictated by the sample roughness and the size and spacing of surface features. In addition, the magnitude and direction of the error in the measured roughness parameters are related to artifact-induced changes in the skew in the distribution of the data points about the surface mean. Significantly, it is shown that either higher or lower roughness values can be measured using a smaller sized tip, depending on the surface character. These model results are supported by sample data obtained with 2 and 10 nm radii of curvature tipped probes on films used in semiconductor research and development. Sharp-tipped probes are clearly beneficial for imaging the surface microstructure...