Development and evaluation of a diamond electron source for electron beam instruments

Since diamonds indicated low or negative electron affinity, they have been expected to be high performance electron emitters. New diamond electron sources have been developed, which are configured for electron beam instruments such as electron beam lithography systems and electron microscopes. As a result of thermionic emission evaluations, an electron emission current of practical level (116 µA at 600 °C) 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 lanthanum hexaborate (LaB₆) cathode and a zirconium oxide/tungsten (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 achieved. The energy spread of a high-current electron beam of over 200 pA generated by field emission from a diamond emitter reached about the same as that of a cold field emission cathode made of tungsten. A scanning electron micrograph (SEM) with a diamond electron source having a tip of submicron order allowed measurement a resolution of 5 nm. It was found that unprecedentedly high-current and high-convergence electron sources could be generated by using diamonds.