Charging Effect of Specimen in Scanning Electron Microscopy

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Abstract
Flat surfaces of MgO and KCl crystals and teflon sheet were coated with gold evaporated films except for the parallel strip areas approximately 200, 100 and 50 µm wide, and the strip areas without coating were observed by SEM at 15 kV. The images of the uncoated areas were distorted by the surface potential caused by charging. The surface potential was quantitatively measured by distortion as a function of the scanning time and width of the strip areas. The results were analysed numerically. Furthermore, it was found that the charging effect was reduced by the tilting angle θ of the specimen with respect to the incident beam. Critical angle θc at which the secondary electron efficiency β equals 1 was experimentally determined as 75°±2° for teflon and 55°±2° for MgO at 15 kV. The deflection effects of the incident and secondary electrons by the surface potential were also discussed by comparing the distortion and contrast for backscattering and emissive mode images.

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