Electron emission characteristics of ZrO/W electron sources with a wide range of tip radii

Emitters of ZrO/W with a wide range of tip radii (0.43-4.2 mum) were prepared and evaluated. A unique tip-forming method using local joule heating was developed to make the tip radii >2 mum. The tip radius dependency of the energy spread agrees qualitatively with the energy spread calculated by Knauer's formula when evaluating the Boersch effect. Emitters with tip radii >2 mum show their energy spread to be close to the theoretically predicted energy spread without the Boersch effect. Even at 400 muA sr(-1) operation, the emitter with a 4.2 mum tip radius shows a 0.47 eV full width at half-maximum (FWHM) energy spread and the emitter with a 0.43 mum tip radius shows a 0.98 eV FWHM energy spread. Emitters with tip radii >2 gm, fabricated by local Joule heating, are expected to suppress chromatic aberration in low beam voltage application and thus would be helpful for industrial uses such as critical dimension and defect review SEM. Copyright (C) 2003 John Wiley Sons, Ltd.