Surface potential measurements of a polymer film following primary ion gun irradiation for ToF-SIMS analysis of insulator using a Kelvin probe and the observation of effects from the vacuum gauge

Abstract

When an insulator sample is analyzed via time-of-flight secondary ion mass spectrometry (ToF-SIMS), charges accumulate on the sample surface due to the primary ion beam. These local surface charges and surface potentials cause many problems during analysis. A Kelvin probe was used to measure the surface potentials of the insulator sample. The surface potential induced on the surface of the sample and its temporal change was measured following the irradiation of the gas cluster ion beam. It was confirmed that the estimated surface potential value is affected by the high vacuum gauge, and there is an inflow of charges that possess polarities opposite to that of the surface potential. The amount of current flowing from the high vacuum gauge was calculated using the surface potential data that was measured. The amount of charge flowing onto the surface of the insulator was varied from several tens of fA to several fA, which was depended on its vacuum degree and position of high vacuum ion gauge. Additionally, neutralization of surface charges by the neutral gas effect was also weakly observed. This leaked current from the high vacuum gauges is likely to have a small but lasting impact on the ToF-SIMS insulator analysis.