ALUMINUM-SILICIDE REACTIONS .1. DIFFUSION, COMPOUND FORMATION, AND MICROSTRUCTURE

Material reactions as a result of thermal treatment were studied on thin-film Al/silicide/Si systems with CoSi2, PtxNi 1-xSi, and MoSi2 for the silicide. Auger electron spectroscopy and Rutherford backscattering analysis showed the transport of Si and the metal released from the silicide into the Al and transport of Al into the silicide. X-ray diffraction showed the formation of Co2Al 9 at 400 °C, PtAl2, NiAl3, and PtNiAl 2 at 275 °C, of which the latter disappeared above 450 °C, and MoAl12 at 535 °C, as well as free Si. The Co 2Al9 formation followed a linear time dependence with an activation energy of 2.3 eV. The MoAl12 formation followed a parabolic time dependence with an activation energy of 3.6 eV. A thin tungsten layer between Al and the silicide proved to be effective as a diffusion barrier below 500 °C, at which temperature WAl12 was formed. The microstructure was studied by scanning and transmission electron microscopy, electron microprobe analysis, and scanning Auger electron spectroscopy. The reaction resulted in the formation of Si islands with a size up to about 10 μm, containing Al-rich inclusions, and the intermetallic compound with Si inclusions in between the islands.