Development of a Diamond Electron Source for Electron Optics Instruments and Evaluation of Energy Spread using the Source

Diamond that shows low or negative electron affinity has good electron emission properties. The authors are developing a diamond electron source, which is suited for electron optics instruments such as electron beam exposure systems and electron microscopes. As a result of thermionic emission evaluations, an electron emission current of practical level (116 μA at 600oC) was obtained. The energy spread of an electron beam generated by thermionic emission was measured as 0.23 eV (FWHM), the value of which was lower than those of a LaB6 cathode and a ZrO/W cathode measured together. The result of field emission evaluations, a practical beam current (459 pA) and stability (6%rms for 10 h) for scanning electron microscope (SEM) was obtained. The energy spread of over 200 pA of a high current electron beam generated by field emission was about the same as that of a tungsten field emission cathode. It was found that an unprecedentedly high current and high convergence electron source can be made by using diamond.