Temperature-dependent residual stresses in a hetero-epitaxial thin film system

• Temperature-dependent residual stress in epitaxial thin film was analyzed using XRD.
• The thermal mismatch is the main cause of temperature dependence.
• The magnitude of residual stress reduces with film thickness at all temperatures.
• At deposition temperature, the residual stress could be in compression or tension.
• The surface defects induced by surface undulation cause additional stress release.

This paper investigates the temperature dependence of residual stresses in a hetero-epitaxial thin film on a sapphire substrate. The X-ray diffraction technique was employed and a theoretical analysis was also carried out. It was found that the magnitude of compressive residual stresses decrease with increasing the temperature, and that the rate of the change can be well predicted theoretically. It was discovered, however, that the residual stresses vary with the film thickness. For a film of 0.3 μm in thickness at all temperatures, the magnitudes of compressive stresses measured are greater than the theoretically predicted; but for that of 5 μm in thickness, the magnitudes measured become smaller than the theoretical. This leads to the conclusion that the mitigation of lattice mismatch, essentially through interface misfit dislocations, could have varied with the change of the film thickness.