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Study on the Scan Field of Modified Octupole and Quadrupole Deflector in a Microcolumn

마이크로칼럼에서 변형된 4중극 디플렉터와 8중극 디플렉터의 스캔 영역 비교

  • Kim, Young Chul (Department of Optometry, Eulji University) ;
  • Kim, Ho-Seob (Department of Information Display, Sun Moon University) ;
  • Ahn, Seong Joon (Department of Information Display, Sun Moon University) ;
  • Oh, Tae-Sik (Department of Information Display, Sun Moon University) ;
  • Kim, Dae-Wook (Department of Information Display, Sun Moon University)
  • 김영철 (을지대학교 안경광학과) ;
  • 김호섭 (선문대학교 정보디스플레이학과) ;
  • 안승준 (선문대학교 정보디스플레이학과) ;
  • 오태식 (선문대학교 정보디스플레이학과) ;
  • 김대욱 (선문대학교 정보디스플레이학과)
  • Received : 2018.08.02
  • Accepted : 2018.11.02
  • Published : 2018.11.30

Abstract

In a microcolumn, a miniaturized electrostatic deflector is often adopted to scan an electron beam. Usually, a double octupole deflector is used because it can avoid excessive spherical aberrations by controlling the electron beam path close to the optical axis of the objective lens and has a wide scan field. Studies on microcolumns have been performed to improve the low throughput of an electron column through multiple column applications. On the other hand, as the number of microcolumns increases, the number of wires connected to the components of the microcolumn increases. This will result in practical problems during the process of connecting the wires to electronic controllers outside of the vacuum chamber. To reduce this problem, modified quadrupole and octupole deflectors were examined through simulation analysis by selecting an ultraminiaturized microcolumn with the Einzel lens eliminated. The modified deflectors were designed changing the size of each electrode of the conventional Si octupole deflector. The variations of the scan field and electric field strength were studied by changing the size of active electrodes to which the deflection voltage was to be applied. The scan field increased linearly with increasing deflection voltage. The scan field of the quadrupole deflector and the electric field strength at the center were calculated to be approximately 1.3 ~ 2.0 times larger than those of the octupole deflector depending on the electrode size.

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Fig. 2. The schematic diagram for (a) a conventional Si octupole deflector, (b) a modified octupole deflector, and (c) a quadrupole deflector, considered in this simulation.

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Fig. 3. Electron beam trajectories obtained by applying deflection voltage to 300 electrodes of the modified octupole deflector (a and b) and quadrupole deflector (c). Deflection voltage is 0 V for (a), and 100 V for both (b) and (c). The column operation conditions are described in text.

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Fig. 4. The variations of deflection field depending on the size (radial angle) of deflector electrode for both octupole and quadrupole deflector structures.

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Fig. 5. The variation of (a) electric potential and (b) electric field strength with the radial distance from the center to the deflector electrode. Deflection voltage is 100 V.

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Fig. 6. The variation of electric field strength according to the angle (size) of the deflector electrode.

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Fig. 7. The relation between the electric field strength at deflector center and the scan field.

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Fig. 1. (a) Conventional microcolumn with Einzel lens. (b) The microcolumn structure used in this work. Einzel lens is eliminated and one additional subsidiary electrode (S2s) is added in source lens.

Table 1. The geometrical dimension of each component and the distance between each component of a microcolumn described in Fig. 1(b).

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Acknowledgement

Supported by : 한국연구재단

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