Multi-electron beam systems

P.Kruit and Ali Mohammadi Gheidari

Delft University of Technology, Faculty of Applied Sciences, Lorentzweg 1, 2628CJ Delft, The Netherlands.

P.Kruit@tudelft.nl

Electron beam instruments give the highest resolution, both in microscopy and in lithography. Their weak

point is the low beam current at high resolution and thus their low throughput. Multi-beam systems can

increase the throughput by orders of magnitude. We have done research for three applications:

1. The MAPPER system for high throughput electron beam lithography [1].

2. A design for massively parallel electron beam inspection [2].

3. A multi beam Scanning Electron Microscope for high speed EBID (electron beam induced

deposition) at sub 5 nm resolution [3].

For multi-electron beam systems the first challenge is to get the right electron source. Everyone would like to use cold field emission sources: very bright, low energy spread and no heating necessary. However, years of research has not produced emitters that are sufficiently stable and reproducible to be useful for multi-beam systems. We have tried to stabilize the beam both by active feedback and by intrinsic feedback in p-doped silicon [4], but there are still very basic problems. For the massively parallel systems (13.000 beams) we use a single thermal cathode in space charge limited emission mode [5]. For the 100 – 200 beam applications we use a Schottky electron emitter, which is brighter but can not supply more than a few micro amps total current. The division of the single beam into many beamlets and the subsequent focusing of the beamlets is done with MEMS components. The requirements on fabrication precision of the optical components is extreme, but within the possibilities of modern semiconductor technology. For lithography, we choose concepts where the only individual control of the beamlets is blanking. This leads to designs for the blanker array where MEMS is combined with CMOS. Lithography and microscopy results of the multi-beam machines will be presented.

References

[1] E. Slot, M.J. Wieland, G. de Boer etal, Proceedings of SPIE Volume 6921, 69211P-1/9 (2008)

[2] Himbergen, H.M.P., M.D. Nijkerk, P.W.H. de Jager etal, JVST B 25(6),2521 (2007)

[3] Zhang, Y., P. Kruit, JVST B 25(6), 2239 (2007)

[4] Teepen, T.F., A.H.V. van Veen, H. van ’t Spijker etal, JVST B, 23 (2), 359 (2005).

[5] Brom, A.J. van den, A.H.V. van Veen, W.M. Weeda etal, JVST B 25(6), 2245 (2007)

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Techinical Digest of IVNC2009

Fig. 1: Example of multi-beam system using a single electron source (from [3] )

Fig. 3: Multi-beam blanker, combining MEMS and CMOS (from [1] )

Fig. 2: Very precise MEMS (Diameter: 100m ~ 100 nm (3))

for multi-beam lenses (from [1] )

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Techinical Digest of IVNC2009