On the impact of sample preparation on scanning spreading resistance microscopy

Scanning spreading resistance microscopy (SSRM) is the method of choice to obtain quantified two-dimensional charge carrier profiles in doped silicon with nanometer-scale spatial resolution. However, quantitative results can be significantly affected by the sample preparation technique. In this work, we present an experimental study demonstrating that previously favored preparation methods can substantially impact SSRM measurements in lightly doped silicon (<1 × 1018 cm−3). It is shown that polishing with aluminum oxide (Al2O3) based consumables significantly raises the sample resistivity at and beneath the prepared surface. This effect was correlated to copper contamination originating from traces in the Al2O3 matrix, as confirmed by SIMS analysis of both the polishing medium and the prepared surface. In addition, prolonged storage in ambient air affects the resistivity beneath the native oxide layer in cleaved samples, whereas samples polished with glycol-based diamond suspensions are less affected. Notably, all reported effects were shown to be partially or fully reversible through low-temperature annealing. Based on these findings, a comprehensive set of recommendations for quantitative SSRM is proposed.