In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines

The formation of Ni silicides is studied by transmission electron microscopy during in situ heating experiments of 12 nm Ni layers on blanket silicon, or in patterned structures covered with a thin chemical oxide. It is shown that the first phase formed is the ${\mathrm{NiSi}}_{\mathrm{2}}$ which grows epitaxially in pyramidal crystals. The formation of NiSi occurs quite abruptly around 400 °C when a monosilicide layer covers the disilicide grains and the silicon in between. The NiSi phase remains stable up to 800 °C, at which temperature the layer finally fully transforms to ${\mathrm{NiSi}}_{\mathrm{2}}.$ The monosilicide grains show different epitaxial relationships with the Si substrate. ${\mathrm{Ni}}_{\mathrm{2}}\mathrm{Si}$ is never observed.