A transmission electron microscopy study of the effects of helium irradiation on polycrystalline and monocrystalline silicon

Abrams, KJ

Abstract

This work is a fundamental study of the effects of helium (He) implantation into polycrystalline silicon (poly-Si). Following implantation, He interaction and vacancy
agglomeration lead to the nucleation of bubbles. Recent scientific literature contains an abundance of papers detailing the effects of He ion implantation, defect formation and the transport of the point defects in crystalline silicon (c-Si) whereas He implantation of poly-Si has been less researched. Our investigations have shown that the atomistic behaviour of poly-Si is different following irradiation with He; this is illustrated by differences in the bubble size distribution and the lack of interstitial clustering. The project arose from an interest in attempting to modify the resonant frequency of mechanical resonators, manufactured using microelectromechanical systems (MEMS) technology, by altering the mechanical properties of Si by ion
implantation. In particular, we were interested in reducing the mean density of the Si by the introduction of significant levels of porosity in the form of helium bubbles.
This thesis reports firstly on the comparative development of irradiation-induced defects (interstitial clusters and He bubbles) in the poly-Si and c-Si under He irradiation. The effects of temperature and fluence are investigated with a view into gaining a recipe for maximum porosities. In addition, both the poly-Si and c-Si were amorphised at the highest irradiation fluences so that the thesis reports secondly on the amorphisation behaviour of the two types of Si under He irradiation at room temperature.

Citation

Abrams, K. A transmission electron microscopy study of the effects of helium irradiation on polycrystalline and monocrystalline silicon. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2011