Effect of focused X-rays on micrometer-thick insulating layers in scanning photoelectron microscopy

Abstract
Focused x-rays on insulating layers produce local charges and the local charges result in kinetic energy shift in photoelectron spectra. In our study, when the thickness of the insulating layers was in the range of micrometer, the amount of kinetic energy shift initially increased within seconds to a value depending on the thickness and chemical composition of the insulator. The amount of energy shift stayed at the same value as long as the insulator was resistant to radiation damage. When the insulator was susceptible to radiation damage, then the amount of energy shift decreased as a function of time. The main cause of this decrease is attributed to conductivity increase due to chemical state change at the x-ray exposed volume of the insulator. The implication of the results is that scanning photoelectron microscopy (SPEM) can be applied for investigation of microstructures containing insulating materials; for example, SPEM can be used for depth-probe conducting microstructures embedded in micrometer-thick insulating layers. This study was performed with a SPEM at the Pohang Light Source, with an x-ray intensity at the focused area of ~10 ⁹ photons/(s. m ²).