Changes in the chemical state of metallic Cr during deposition on a polyimide substrate: Full soft XPS and ToF-SIMS depth profiles

Abstract

We demonstrate the effectiveness of the combination of depth profile analyses based on soft X-ray photoelectron spectroscopy (XPS) with Ar+ sputtering and time-of-flight secondary ion mass spectrometry (ToF–SIMS) with Cs+ sputtering, to determine the changes in the chemical states of Cr nanofilms during deposition on a polyimide (PI) substrate, with nanoscale-depth resolution. The XPS and ToF-SIMS depth profiles obtained show evidence of preferential oxygen sputtering during Ar+ and Cs+ bombardment. Therefore, detailed analyses of the depth profiles and spectra were performed with consideration of the results of cross-sectional electron energy loss spectroscopy and non-destructive hard XPS for the same sample. As a result, the depth profiles for Cr, Cr2O, Cr2O3, Cr(OH)3, and CrO3 in the Cr film were successfully differentiated with nanoscale resolution. At the deeper area, the ratio of Cr2O3, Cr(OH)3, and CrO3 decreases, while that of Cr metal and Cr2O increases, which was caused by Ar+ and Cs+ sputtering. The presence of the Cr2O phase in the Cr film was revealed, regardless of the preferential sputtering. These results are very useful for optimization of the Cr/PI bilayer fabrication process, which is one of the most important components in flexible electronics.