Gas effect on the emission and detection of the backscattered electrons in a VP-SEM at low energy

•Increasing pressure makes backscattering coefficient to increase at specimen top surface and decrease at the detector.•Increasing pressure makes the BSE exit zone to extend at the specimen top surface.•At 5 kV accelerating voltage and up to 1000 Pa, no effect is found under helium.•A new approach is proposed to determine the operating pressure range for the best resolution. The effect of the electron beam skirting on the emission and detection of the backscattered electrons (BSE) in a low vacuum scanning electron microscope is investigated at low energy regime. Monte Carlo computed dependencies of the BSE distribution on the water vapor and air pressure shown a significant increase of the extent of the BSE exit zone. The pressure variation has however a little effect when helium gas is used. A new approach based on the comparison between the sizes of the skirt and the BSE exit zone on the specimen surface provides a useful tool to determine the operating pressure range that ensures minimal degradation of the lateral resolution in BSE imaging mode.