Charging effects in the secondary ion mass spectrometric analysis of targets containing low-conductivity regions

Abstract

Common ion sputtering techniques for depth profiles can cause buildup of charge in low-conductivity regions such as p-n junctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of 69Ga+ and 27Al+ in the low-conductivity region of these Zn-diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron-induced secondary electron coefficient of GaAlAs is larger than unity.