INVESTIGATION OF SURFACE CHARGING OF INSULATING MATERIALS DUE TO SECONDARY PARTICLE-EMISSION USING A NEW DUAL BEAM INSTRUMENT

A new instrument has been developed to study the characteristics of charge build-up on insulating materials caused by the sputtering of secondary particles by ion, electron, neutral or photon beams. The instrument utilizes two beam lines: the charging ion beam irradiates the sample while a measurement ion beam is passed parallel to the sample surface and is then deflected by the charge on the sample. The deflection of the measurement beam, which is proportional to the charge on the sample, is measured with a microchannel plate and photodiode array combination. For these experiments the instrument was configured to simulate a secondary ion mass spectrometer using a negative ion primary beam and a secondary ion extraction lens element. The charge build-up on Mylar and Teflon bulk films was measured as a function of extraction voltage and the results were analyzed using the SIMION ion optics code. The samples could be charged negative or positive, depending upon extraction voltage, and the dominant parameter controlling the charging was the shape of the potential field near the sample. The results indicate that the extraction voltage and the design of the sample mount and near-field regions are the important factors controlling sample charging.