Comparison of areal measurements of the same zone of etched Si and hydroxyapatite layers on etched Si using different profiling techniques

Abstract

In the field of areal surface roughness measurement, characterization using several techniques can be helpful to better understand the performance of each technique and to improve the overall precision. Measuring exactly the same area with different techniques in practice is not easy. Such studies are of great interest in order to characterize and to understand important new materials today such as semiconductor alloys and graphene for silicon technologies, or biomaterials such as hydroxyapatite for use in human implants. In this work, two types of samples based on a silicon wafer were made by marking with a fractal, multi-scale photolithographic mask and etching. The first sample consisted of a bare silicon wafer with a pattern consisting of 2.4 µm deep numbered square features. The second sample was a rough layer of hydroxyapatite deposited from a solution of simulated body fluid on a similarly etched silicon wafer. The same zone of several squares on the two samples were measured by interference microscopy, AFM and ESEM. The 2D cross sectional profiles and 3D views from the different results were then compared using different analytical measurement software tools. While the general shapes of the measured microstructures were similar, several differences also appeared. Variations were found of up to 7 % in the depths of the etched features measured with the different techniques. This is ascribed to instrumentation calibration errors, probe/surface interactions and to differences in measurement procedures between the software used. Artifacts were also visible at square edges due to probe/source interactions.