Physico-chemical characterization of multilayer YIG thin film deposited by rf sputtering

Yttrium iron garnet (YIG) film made as a magneto-optical medium suffers from the problem of crack formation, caused by the heating process. YIG thin film is deposited by radio frequency rf magnetron sputtering; the obtained layer is amorphous and it needs annealing to be crystallized. After heat-treatment at 740 ◦C of the sample realized on quartz substrate, we observe cracks on the entire film surface. This is due to the large difference between the thermal expansion coefficient (5.5 × 10 −7 K −1 for quartz and 10 × 10 −6 K −1 for YIG). In this paper we present a new fabrication method to reduce this problem, we make a multilayer to obtain at the end a uniformly unique layer with excellent crystalline structure. Such films have the possibility to reach a thickness of 500 nm. YIG films have been studied by Rutherford backscattering spectrometry (RBS), optic ellipsometry and the scan electron microscope. The RBS spectra were collected in channelling geometry with incident particles energy 2 MeV and 3.5 MeV. The thickness and the stoichiometric value of the thin films have been evaluated. Simulation of all spectra indicates a constant composition. Ellipsometry method is well adapted to model the thin film structure layers, and to measure the thickness of the film and the complex index of refraction. The theoretical ellipsometric value of the index of refraction is (2.22) while the experimental value is ranging from 2.2 to 2.3 for a wavelength of 1550 nm.