Single pole-piece objective lens with electrostatic bipotential lens for SEM

This report describes the characteristics for the development of a compound lens that consists of a single pole-piece objective lens and an electrostatic bipotential lens. By applying a relatively small voltage of around 1 kV to the specimen and the bipotential lens, the image quality for low acceleration voltage is improved to a condition better than with just a single pole-piece lens. Even if the wafer is tilted to a large angle, the electric field near the specimen does not become asymmetrical, and there is no occurrence of astigmatic aberration or a reduction of the secondary electron signal. Therefore, 300 mm diameter wafers can be tilted with large angles to observe patterns, particles and defects with high-resolution SEM. Lastly, when the specimen is not tilted, a topographic image of the specimen surface can be obtained by detecting the secondary electron with dual detectors.