Evaluation of silicon nitride as a diffusion barrier for Gd-Si-Ge films on silicon

Synthesis of thin film of magnetocaloric Gd-Si-Ge alloy has been investigated for use in miniature magnetic coolers. PECVD Si3N4 films were deposited on Si(100) substrates. Next thin films of Gd5Si2Ge2 (GdSiGe) were sputtered from a stoichiometric, magnetocaloric Gd5Si2Ge2 target. After deposition, the films were ex situ annealed to (a) investigate the stability of the diffusion barrier and (b) to obtain Gd5Si2Ge2. Samples of Si/300 nm Si3N4/100 run GdSiGe were prepared and annealed in vacuum between 700 and 1150 degrees C. The structure and morphology of films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The interface of annealed sample (1150 degrees C) was analyzed using secondary ion mass spectrometry (SIMS). Results show that while the magnetocaloric phase does form, silicon nitride does not serve as a stable diffusion barrier in the GdSiGe/Si3N4/Si system.