Ion energy distribution near a plasma meniscus for multielement focused ion beams

Abstract

The axial ion energy spread near a plasma meniscus for multielement focused ion beams is investigated experimentally in atomic and molecular gaseous plasmas of krypton, argon, and hydrogen by tailoring the magnetic field in the region. In the case of magnetic end plugging, the ion energy spread reduces by ∼50% near the meniscus as compared to the bulk plasma, thereby facilitating beam focusing. A quadrupole filter can be used to control the mean energy of the ions. Comparison with standard Maxwellian and Druyvesteyn distributions with the same mean energy indicates that the ion energy distribution in the meniscus is deficient in the population of low and high energy tail ions, resulting in a Gaussian-like profile with a spread of ∼4 and ∼5 eV for krypton and argon ions, respectively. By carefully tuning the wave power, plasma collisionality, and the magnetic field in the meniscus, the spread can be made lower than that of liquid metal ion sources, for extracting focused ion beams of other elements with adequate current density, for research and applications in nanosystems

Micron-focused ion beamlets

“…The plasma production in this system and its utilization as a source for single FIBs has already been demonstrated. [9][10][11] To extract multiple ion beamlets, we have designed a plasma electrode ͑PE͒ with a honeycomb-like pattern which contains apertures at the vertices and at the center of a hexagon ͓as shown in Fig. 2͑b͔͒.…”

“…22 The input parameters to the simulations have been obtained from our experiments using the plasma ͑ion͒ source. [9][10][11] The simulation results are then compared with electrostatic ray optics model calculations. 23,24 Finally an experimental set-up is described which will be used to make first beam tests on utilizing the MBES system.…”

“…A compact microwave plasma based ion source for FIB systems has been developed, which yields a stable and high density plasma in a compact cross section, [9][10][11] providing reasonably good beam current for FIB applications. For example, using conventional LMIS based FIB with a 10 pA/30 keV gallium beam the mill rate of silicon ͑normal incidence͒ is only 2.7 m 3 / s, 12 but using a plasma based FIB the current at the substrate can be made orders of magnitude larger ͑ϳtens of microampere͒ and the time is greatly reduced for volume milling.…”

Localized subsurface modification of materials using micro-low-energy multiple ion beamlets

“…Recently, generation and characterization of a multi element single focused ion beams from compact microwave plasma ion source has been demostrated, [28][29][30] where beam spot size of ∼20 μm and beam current ∼ 1 -10 μA 31 were obtained. Ions of different elements can be generated from the same source by using different gas and at a time only a single species of ion beam can be obtained.…”

“…The small ion energy spread (∼ 5 eV) at the plasma meniscus from where the beams are extracted is an added advantage. 29,30 The possibility of obtaining low energy micron size multi ion beamlets has been recently demonstrated 32 using simulation codes.…”