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This article presents a study of the influence of the sputtering parameters on the preferred orientation of polycrystalline aluminum nitride thin films. Aluminum nitride films were grown by rf reactive sputtering of an aluminum target in an N2/Ar gas mixture for different values of the deposition parameters: total pressure, nitrogen content in the discharge gas, and substrate bias voltage. The preferred orientation of the films was analyzed by x-ray diffraction. Films with different preferred orientations were obtained, ranging from c-axis oriented films to films with the c axis tilted by up to 61.6° from the substrate normal. The different mechanisms influencing the preferred orientation of the films have been considered, especially the transfer of energy to the adatoms on the substrate by particle bombardment. An analysis of the relation between the deposition parameters and the crystal orientation has allowed us to determine the relative importance of the different particles in the supply of energy to the substrate. We have found that Ar ion bombardment of the film during growth is the most influential mechanism on the preferred orientation of the films. As bombardment becomes more energetic, microcrystals in the film tend to grow with the c axis along the surface normal. The energy of Ar bombardment can be best controlled through the substrate bias voltage, a characteristic that we have employed to obtain AlN films exhibiting pure (00.2) preferred orientation and rocking curves with a full width at half maximum as low as 4.2°.

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Articles you may be interested inSynthesis and characterization of 10nm thick piezoelectric AlN films with high c-axis orientation for miniaturized nanoelectromechanical devices Appl. Phys. Lett.

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AlN layers were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. Crystal quality was assessed by atomic force microscopy and high resolution x-ray diffraction. The III/V ratio and the growth temperature, rather than thickness and growth rate, are found to be critical parameters to achieve good quality AlN layers. III/V ratios close to stoichiometry, and high growth temperatures (⩾900 °C) lead to optimal AlN layers. The growth rate is barely modified when growth temperature changes from 780 to 920 °C, but the growth mode and surface roughness are strongly affected. Optimal AlN layers have full-widths at half-maximum values of 10 arcmin, and an average surface roughness of 48 Å.

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