An in-situ TEM study of the effects of 6 keV He ion irradiation on Si and SiO₂

Using the new MIAMI facility (Microscope and Ion Accelerators for Materials Investigations) at the University of Huddersfield, an in-situ TEM study has been carried out on the effects of helium implantation on a tri-layer system consisting of monocrystalline silicon (c-Si), silicon dioxide (SiO₂) and polycrystalline silicon (poly-Si). Co-irradiation of these three components enabled direct comparisons to be made of differences between the response of c-Si and poly-Si to the He irradiation; in particular, differences in the development of interstitial clusters and bubbles and eventual amorphisation. For implantations to high fluences (>10¹⁷ ions/cm²), very significant levels of porosity were observed to build up in the Si, leading to changes in the width of the Si layers of up to 29% Although no helium bubbles were formed in the SiO₂ layer, a very significant dimensional change (but in this case an observed shrinkage) also occurred in this material. Finally, room temperature amorphisation of the Si was observed at high fluences, beginning at somewhat lower fluences in the poly-Si than in the c-Si. A brief discussion of the origins of these effects is presented.