Surface analysis insight note: Initial, statistical evaluation of X‐ray photoelectron spectroscopy images

Abstract

With advances in instrumentation and image processing, imaging X‐ray photoelectron spectroscopy (XPS) is becoming increasingly important in surface analysis. In this Insight Note, we suggest the following three steps for the initial evaluation of XPS images: (i) Plot all the data. Possible plots here include an overlay plot, a plot of the average and standard deviation of the spectra, a waterfall plot, and a contour plot. (ii) Examine slices through the data cube at different binding energies, identifying those that show significant contrast. (iii) Examine the spectra, including their average and standard deviation, in defined regions of slices through the data that show contrast. These steps allow XPS images to be probed without the use of more sophisticated exploratory data analysis (EDA) techniques. Indeed, these steps may set the stage for additional EDA analysis of XPS images. Furthermore, they provide an initial understanding of an XPS image that stays close to the original data. Our three‐step protocol was applied to an XPS image of a region of a silicon wafer with different oxide thicknesses. This image primarily contained two types of pixels/regions: one of silicon with a thin oxide layer and the other of silicon with a thicker oxide layer. We emphasize the importance of contour plots of all the data and examining the average and standard deviation of regions of contrast in slices through the data cube.