Interface constraint effect and stress relaxation in nano-sandwiched thin film

Micro-particles and nano-wires, small outgrowths were found to appear on upper film surface when metal thin film is confined between two Si₃N₄ layers deposited by magnetron sputtering and is annealed at an appropriate temperature. The stress evolution during this process is monitored by multi-beam optic stress sensor, and is qualitatively interpreted in terms of elastic and plastic deformation, as well as bulk diffusion. Additionally, the interface constraint effect among different layers is explored. Stress relaxation of nano-sandwiched thin films behaves in different stress modes. As a comparative study, Si₃N₄/Zn/Si₃N₄ sandwiches were prepared and studied by the same method. Experimental results show that the pertinent geometry is strongly dependent on material types and stress states of the substrates. Finally, an appropriate mode was suggested to interpret this phenomenon.