On the stability of thin epitaxial NiSi2 layers on Si (111)

By repeated deposition of several Å of Ni below 100 °C and subsequent annealing to typically 350 °C, thin continuous NiSi₂-layers have been grown epitaxially on Si (111). Thicknesses exceeding ∼- 70 Å require a different procedure due to the increasing importance of lateral growth, spoiling the layer quality. We show that MBE at substrate temperatures above 500 °C is not a viable technique to increase the thickness of the ultrathin layers. The reason is found to lie in the insufficient stability of the NiSi₂ templates, disintegrating into islands at temperatures above 500 °C. Perfectly smooth layers up to 1000 Å have, however, been grown by a new method in which alternate layers of Ni and Si (typically 1 Å and 4 Å respectively) are deposited onto the initial template at substrate temperatures between 350 °C and 380 °C.