Lanthanum silicide formation in thin La-Si multilayer films

Alternating layers of Si (200 A thick) and La (200 A thick), up to 20 layers altogether, were deposited by electron evaporation under uhv conditions on Si(100) substrates held at 150°C. Isothermal, rapid thermal annealing has been used to react these La-Si multilayer films. Intermixing of these thin La-Si multilayer films has occurred at temperature as low as 150°C for 2h when annealed. Increasing the annealing temperature from 150 to 400°C for 1h, LaSi2 forms gradually and the completion of reaction occurs at about 300°C. The determination of the compound stoichiometry by backscattering yields a formulation close to La-Si2.2. During the formation of LaSi2 from 150-400°C, there is some evidence for small grains in the selected area diffraction patterns, indicating that LaSi2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial LaSi2 layers when reacted in the solid phase even after RTA (900°C) for 10s.