Two-dimensional dopant imaging of silicon carbide devices by secondary electron potential contrast

Abstract

Dopant profiling and two-dimensional imaging of device cross-sections are relevant activities for the development of new power semiconductors and especially of silicon carbide devices. Unlike silicon, SiC presents extreme physical properties, which make the common electrical dopant profiling techniques either poorly reliable or non viable. Recently, Secondary Electrons Potential Contrast maps produced by Scanning Electron Microscopy (SEM) emerged as a powerful tool for two-dimensional quantitative dopant imaging. In this work SEPC is applied for the first time to characterize fully functional power devices with particular focus on MOSFET and JFET. The main component of the SEPC arises from the difference in the built-in potential between differently doped regions. This produces a stray electric field irradiating from the surface of the semiconductor sample, which either accelerates or retards the low-energy secondary electrons depending on their emission site. The use of a SEM equipped with a dedicated energy filter for secondary electrons enhances the observed contrast, which is already particularly intense in wide-bandgap semiconductors, where the density of intrinsic carriers is very low. In the case of SiC, the contrast is sufficiently intense to resolve both p–n and unipolar junctions.