Study of interdiffusion in thin Fe film deposited on Si(111) by x-ray reflectivity and secondary ion mass spectrometry

We report on the effect of annealing on a thin Fe film deposited on a Si(111) substrate, using x-ray reflectivity and secondary ion mass spectrometry (SIMS) techniques. Using Fourier transform of the x-ray reflectivity data, we have estimated the layer thickness of the film. From the estimated thickness and critical value of the scattering vector $q_c$ obtained from the reflectivity data, an initial guess model of the electron density profile of the film is made. Using an iterative inversion technique, based on the Born approximation, with the obtained initial guess model, we have extracted the actual electron density profile of the film as a function of depth from the specular x-ray reflectivity data. On annealing, we observe interdiffusion of Fe and Si resulting in an increase in the thickness of the film. We have also carried out a SIMS measurement on the annealed sample to support the result of the annealing effect observed from the analysis of x-ray reflectivity data. The SIMS analysis indicates that the top of the film is rich in Si which has diffused from the substrate to the surface of the Fe film on annealing.