Low-Temperature Migration of Silicon in Metal Films on Silicon Substrates Studied by Backscattering Techniques

The backscattering method using 2-MeV^(4)He^(+) ions is employed to obtain microscopic information about solid-solid reaction of Si with thin layers (200∼4000 A) of Au, Ag, and Al which are vacuum evaporated onto Si crystal substrates. The interesting observation is the migration of Si atoms into these metal films at temperatures (for example, 150°C in Au, 400°C in Ag) well below their eutectic points (375°C for Au and 850°C for Ag). This phenomenon also indicates that at these low temperatures the dislodgment of Si atoms from tightly bound Si crystal does occur. Our experiments clarify that the origin of this effect is the interaction of Si with metals at the interface.