The effect of thermal treatment on the thin-film reaction of La, Ce, and Nd on silicon surfaces

Abstract

The formation of rare-earth metal (REM) silicides prepared by dual electron beam evaporating La, Ce, and Nd under UHV on Si(111) and Si(100) has been studied using Auger electron spectroscopy depth profile, Rutherford backscattering spectroscopy, x-ray diffraction and transmission electron microscopy (TEM) techniques. Each sample had an additional thin layer of either Si, Mo, or Nb deposited on top of the REM layer to protect the REM layer from oxidation. Isothermal, rapid thermal, and laser annealing have been used to react REM overlayers. With the isothermal annealing, REMs reacted and intermixed with Si at temperatures as low as 200 °C for 60 min, but the disilicide phase confirmed by the x-ray diffraction did not emerge until the annealing temperature was raised to 600 °C for 60 min. Therefore, an intermediate stage of formation existed for samples annealed at 200–600 °C before the formation of the disilicide final reaction product (REM Si2−x) occurred above 600 °C. The experimental data show that the thermal processing can influence strongly the formation of REM silicides, the interface chemical reaction and interdiffusion. Cross-sectional TEM micrographs of interfaces formed by isothermal, rapid thermal, or laser annealing clearly identify these differences. The rapid thermal annealed and laser annealed interfaces are both flat and uniform, while the isothermal annealed interface is rough and exhibits a wavelike variation in interface plane location.