Influence of ion induced amorphicity on the diffusion of gold into silicon

Abstract

It is experimentally demonstrated that, after ion irradiating 60nm thick Au films on Si substrates with 230keV Ar+ ions, annealing conditions can be found leading to strong diffusional contrasts between bombarded and unbombarded areas. While Au readily diffuses into the bombarded part of the sample at 310°C, its diffusion is still completely blocked under identical conditions in the unbombarded parts. Clear evidence is provided that this diffusional contrast is due to bombardment induced amorphization of the underlying Si substrate. The amorphous Silicon (a-Si), however, has to extend right to the Au∕Si interface, since any intermediate crystalline layer will suppress the diffusional contrast. An example for this latter situation is realized by performing the ion bombardment prior to the evaporation of the top Au layer leading to a still crystalline Si surface layer, which is found to act as a barrier against Au diffusion at 310°C. In accordance with the idea that a-Si, independent of its specific preparation, causes the observed Au diffusion enhancement, the effect is also found for a-Si prepared by evaporation at ambient temperature. In that case an even higher Au diffusion coefficient is obtained than for Si amorphized by ion bombardment pointing to subtle structural differences between both types of amorphous Si.

Ion-beam-induced enhanced diffusion from gold thin films in silicon

“…Similar conclusion is available from the experiment of Ehrhard et. al, with a thick Au layer deposited on c-Si, a-Si and partially a-Si [6]. It was clearly shown that Au diffusion from top Au layer is more in a-Si than in c-Si and any intermediate crystalline layer (that is partially a-Si) will suppress the effect.…”

“…Two mechanisms, namely the 'Frank-Turnbull' mechanism [2] and the 'kick-out' mechanism [3], have been used to explain the gold atoms' diffusion in crystalline silicon. In the case of amorphous silicon, the Au diffusion was explained in terms of direct diffusion, wherein the diffusing Au atoms were temporarily trapped by different kinds of vacancy-like effects [4,5]. In general, at high enough temperatures, the amorphous silicon (a-Si) recrystallizes and hence it would be difficult to study the diffusion of gold atoms in an a-Si system.…”

“…Two mechanisms, namely, "kick-out" mechanism [3] and "Frank-Turnbull" mechanism [4] have been used to explain the gold atoms diffusion in crystalline silicon. Similar understanding of diffusion of gold in amorphous silicon (a-Si) is not well understood [5,6].…”

Au Nanoparticle Formation from Amorphous Au/Si Multilayer

“…We used D(T) in the previous study [31]. Unknown parameters are ∆G and c(T) in Equation (5). From 480 to 600 K, we assume that ∆G in Equation 5is approximately expressed by a weak linear relation with temperature ( 0 1ΔG k k T = + ).…”

“…In metal silicides, metal-induced crystallization (MIC) [1]- [5] in thin films is well known to be a fundamental phenomenon relating to low eutectic point. Rather than viewing this phenomenon from a solid-phase reaction perspective, studies from the diffusion process view point are necessary due to the fact that electric screening weakens the covalent bonds of the amorphous Si (a-Si).…”