The goal of this study is to develop a multi-beam microcolumn for parallel e-beam lithography and intend to solve the electron emission uniformity problem as well as increasing the throughput requirement. We have designed, simulated, and fabricated an electrostatic lens integrated multi-electron beam array with Schottky emitters. Schottky emitters operate at a relatively high temperature and requires less electrical field than that of field emitters to achieve the same emission brightness. The low electric field operation will reduce the ion bombardment damage of the emitter. In the case of a gated field emitter with a narrow gap, high electric field causes serious damage due to breakdown on the insulator. In order to solve this problem, we fabricated the gated Schottky emitters with large gap. The capability of the low electric field operation of the Schottky emitters makes such structure practical.
The Schottky emitter array consists of mutiple layers, including boron-doped diamond heaters with a diamond tip (emitters), Si micro gate array (extrators) and Si focusing lenses. The critical components are microfabricated and monolithically integrated base on (micro electro-mechanical system) MEMS technology. When the emitters are heated, the potential barrier become small due to thermally excited electrons, which reduce the electric field for electron emission. Electrical Si lenses are formed in front of the gated emitter to focus the electron beam into a small spot.
Electron emission performance of the fabricated diamond emitter was characterized. As increasing the heating current into the heating element with the emitter, the emission current increases. When heating the diamond emitter at a voltage of 2.8 V, an emission current of 490 nA has been observed at an electric field of 0.36 V/µm. By fitting the measure data with Schottky emission models (Richardson-Dushman equation), the temperature at the emitter was calculated to be 1680 °C. The emission stability was monitored for 20 hrs, the fabricated diamond Schottky emitter provides a stable emission current. It is found that the long term stability within a variation of 2 %/h was obtained in this heated diamond emitter.
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