Formation of amorphous layers by solid-state reaction from thin Ir films on Si(100)

The initial stages of thin Ir film/Si(100) reaction are studied by means of grazing incidence X-ray reflection and transmission electron microscopy. We observe amorphous layers between the Ir film and the Si(100) substrate already to be present after deposition at high vacuum and at ultra-high vacuum conditions. At room temperature an amorphous interlayer forms with an thickness of about 2 nm. Deposition at 400 degrees C results in an 8-nm-thick amorphous layer in which crystallites are present. The formation of the amorphous phase can be explained by calculating the reduction of free energy when an amorphous mixture of Ir and Si atoms is formed. To investigate intermixing of Si and Ir atoms, we use impurities as markers and conclude that during room-temperature-deposition Ir atoms move into the Si(100) substrate. During annealing of room-temperature-deposited samples at 500 degrees C, Si outdiffusion is predominant.