Elevated-temperature X-ray Diffraction Analysis of Strains/Stresses in Heteroepitaxial AlN Thin Films on (0001) Sapphire

AlN thin films on sapphire substrates are studied at high temperature using in-situ X-ray diffrac-tion. Lattice parameters, residual stress, and thermal expansion coefficients are determined for the AlN thin film where significant expansion and stress are found at higher temperatures.

There is a considerable interest in the characterization of AlN thin films due to their outstanding electronic, mechanical and chemical properties as well as due to the great potential of AlN as a wide band gap semiconductor and as a surface protective coating. For the semiconductor and mechanical applications of AlN thin films, residual stress is one of the most important factors decisively influencing hardness, toughness, thin film adhesion to the substrate and band-gap characteristics. Generally, it is supposed that the stresses in AlN thin films result from the film growth procedure (growth stresses) and the cooling down to room temperature after deposition (thermal stresses). For practical application of AlN films, the control of residual stresses by varying deposition conditions is of utmost importance and there is a need for experimental methods allowing to quantify contributions of different strain/stress phenomena to the total strain/stress in the films. With the DHS 1100 heating attachment, high-temperature X-ray diffraction (XRD) analysis of strain in heteroepitaxial AlN thin films on sapphire substrates has been possible. The temperature dependencies of strains/stresses allowed to estimate contributions of growth and thermal stresses to the total stress in the films.

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