Analyzing residual stress in bilayer chalcogenide Ge₂Se₃/SnTe films

Chalcogenide thin film stacks of polycrystalline SnTe and amorphous Ge₂Se₃ are analyzed for residual stress using X-ray diffraction. The as-deposited film stacks are annealed at different temperatures and the thermal dependence of stress is investigated. Stress evaluations are performed by employing the sin² ψ technique using a 2D area detector system. As-deposited samples are found to be compressively stressed and exhibit increasingly tensile thermal stress with increasing annealing temperature. Onset of crystallization of the bottom Ge₂Se₃ layer is indicated by a sharp drop in the stress level in the 270 °C-360 °C temperature range, due to volume shrinkage associated with the crystallization. Diffraction patterns of samples annealed at different temperatures indicate compositional changes that are attributed to inter-diffusion of ions between the two layers. The XRD profiles of samples annealed at 360 °C and 450 °C indicate the formation of a Ge₂Se₃-SnTe solid solution. It is suggested that both, residual stress and temperature dependent compositional changes affect the measured d spacings.