The principle and test results of a large-raster no-mesh return-beam electron-camera readout system

An electrostatic deflecting lens (EDL) return-beam, electron-camera readout system has been developed and tested. The unique features of the system are the following: 1) there is no field stopping mesh used, therefore, ultra-high resolution becomes possible; 2)the normal landing condition is obtained by making the deflection center coincide with the focal point of the final lens; 3) a large number of beam spot diameter scans are obtained; and 4) magnification factor of the system M is smaller than one. The system was tested at electron landing energies from 70 V to 14 kV. In a 2.86 cm × 2.86 cm raster scan, the typical on-axis modulation transfer function (MTF) at a spatial frequency of 100 lp/mm is 0.67 for high-energy landing and 0.55 for low-energy landing. The linear scan is better than 7000 spot diameters at high-energy landing and around 6000 at low-energy landing. The test results indicate that with some design modification, the EDL system can be used for low-energy surface-scanning electron-microscope (SEM) applications.