Control of the preferred orientation of AlN thin films by collimated sputtering

Abstract

The effects of collimation on the crystallographic orientation of sputtered aluminum nitride thin films have been studied. The AlN films were deposited on glass at a total gas pressure of 15 mTorr using a rf-diode sputtering system. Collimators with angular widths varying from 31° to 140° were used to decrease the range of impingement angles of the flux of species sputtered and reflected from the sputtering target that arrive on the film surface. The three-dimensional crystallographic orientation of the films was studied by the x-ray pole figure method. All the AlN thin films were deposited under similar conditions, with and without collimators, and produced polycrystalline structures with the c-axis (0001) direction perpendicular to the substrate surface. A comparison of the films’ preferential orientations showed that, as the angular width of the collimator decreases, the full width at half maximum (FWHM) of the χ scan profile of the 0002 diffraction peak decreases linearly, indicating a better alignment of the crystallites in the collimated samples. For a film deposited with a collimator of angular width of 31°, the FWHM is 16°, compared to 33° for a noncollimated deposited film under otherwise identical conditions. For films deposited with a rectangular collimator, crystallites orient in an asymmetric distribution which is directly related to the asymmetry of the collimator opening.