Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

Abrams, K. J., Hinks, J. A., Pawley, C. J., Greaves, G., van den Berg, J. A., Eyidi, D., Ward, M. B. and Donnelly, S. E. (2012) Helium irradiation effects in polycrystalline Si, silica, and single crystal Si. Journal of Applied Physics, 111 (8). 083527. ISSN 00218979

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Abstract

Transmission electron microscopy (TEM) has been used to investigate the effects of room
temperature 6 keV helium ion irradiation of a thin (�55 nm thick) tri-layer consisting of
polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the
TEM under conditions where approximately 24% of the incident ions came to rest in the specimen.
This paper reports on the comparative development of irradiation-induced defects (primarily
helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides
direct measurement of a radiation-induced increase in the width of the polycrystalline layer and
shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to
the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiationinduced
viscoelastic flow processes in the silica under the influence of stresses applied by the
swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion
irradiation; however, this is estimated to be a relatively minor effect with swelling and stressrelated
viscoelastic flow being the dominant mechanisms of dimensional change.

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