Surface morphological influence on charging at metal–insulator interface in XPS depth profiling

Charging in depth profiling in X-ray photoelectron spectroscopy (XPS) for metal layers on insulated substrates (Au/Cr/SiO2 (quartz)) was studied both with and without conduction between a specimen and a spectrometer (i.e., the conducting mode and the floating mode). Using a neutralizer, differential charging and electrical interface ‘‘charge jump’’ were simultaneously observed at the Cr/SiO2 interface in the conducting mode. In contrast, in the floating mode differential charging was avoided after the charge jump. By AFM performed in the tapping mode for phase ex situ observation, the layer Cr distribution before charge jump was apparently changed to the island distribution after the charge jump. This surface morphological change due to a heavy sputtering process is considered to be the origin of the observed differential charging and the charge jump. Thus, it is concluded that charging is strongly related to the surface morphology in XPS depth profiling for metal layers on insulated substrates. Hence, in XPS depth profiling for a sample with a metal–insulator interface, the floating mode performance, which is attained by insulating a sample from the spectrometer, is desired to keep the surface potential of the sample uniform. # 2004 Elsevier B.V. All rights reserved