Measurement of insulator surface potential using time-of-flight secondary ion mass spectrometry

In this study we demonstrate a technique which determines the absolute electrostatic potential of the surface of insulating samples analyzed by time-of-flight (TOF) secondary ion mass spectrometry (SIMS). Small changes in surface potential from the nominal sample bias of 500 V were deduced from shifts in the TOF spectra by use of a large extraction distance and modified ion mirror design. Experimental peak shapes and shifts were duplicated by modeling the ion flight times throughout the mass spectrometer to confirm the results. By monitoring peak positions we were able to adjust charge compensation parameters, thereby keeping the surface potential at the desired value. This technique offers the opportunity to investigate the fundamentals of sample charging, or can be used to evaluate the effectiveness of charge compensation during SIMS analysis of insulators.