Lanthanum Silicide Formation In Thin La-Si Multilayer Films

Alternating layers of Si (200 Å thick) and La (200 Å 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 1 h, LaSi 2 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Si 2.2 . During the formation of LaSi 2 from 150–400°C, there is some evidence for small grains in the selected area diffraction patterns, indicating that LaSi 2 crystallites were present in some regions. However, we have no conclusive evidence for the formation of epitaxial LaSi 2 layers when reacted in the solid phase even after RTA (900°C) for 10 s.