Gold-silicon phase diagram

FIGURE 8.10 The gold-silicon phase diagram (Courtesy of ASM International). 

Silicon is soluble in aluminum in the solid state to a maximum of 1.62 wt % at 577°C (2). It is soluble in silver, gold, and 2inc at temperatures above their melting points. Phase diagrams of systems containing silicides are available (2,3). 

Massalski and Prince selected this particular phase diagram because of its simplicity for illustration and because this particular phase diagram is of considerable importance in the semiconductor device industry. Silicon chips are frequently bonded to a heat sink, using a gold alloy or more frequently a Au-Si alloy foil placed between them. Upon heating above 163 C. the Au reacts with Si to form a brazed joint between the silicon chip and the heat sink. 

Figure 6.62. Silicon nanowire growth from a gold nanocluster catalyst. Shown is (a) the phase diagram for the Au/Si system, showing the eutectic temperature/composition (b) SEM image and (c) high-resolution TEM image of the nanowires grown at a temperature of 450° C. The dark tip of the nanowire is from the gold nanocluster. Reproduced with permission from Hu, J. Odom, T. W. Lieber, C. M. Acc. Chem. Res. 1999, 32, 435. Copyright 1999 American Chemical Society.

The alloy of the metallic intermediate layer is in many applications based on a composition of silicon (Si) with gold (Au) or aluminum (Al). Furthermore, there are other alloy compositions, which are each associated with a specific melting temperature. In a phase diagram, the melt temperature of the phases as a function of the concentration of alloying elements as well as the concentration ratios is plotted. Figure 1 shows the Au-Si alloy system with the corresponding phase diagram. 

Okamoto H, Massalski TB (1990) Au-Si (gold-silicon). In Massalski T, Okamoto H, Subramanian P, Kacprzak L (eds) Binary alloy phase diagrams, vol 1. ASM International, Materials Park, pp 428-431... 

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