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 ͑0001͒ 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 ͑FWHM͒ of the 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.

Competitive growth mechanisms of aluminum nitride thin films deposited by off-normal reactive magnetron sputtering

“…2,3 Owing to its convenient properties, AlN is used to fabricate surface acoustic wave and optical devices. 4 It is a compound semiconductor and has a hexagonal wurtzite structure. Its lattice constants a and c are 3.11 and 4.99 Å, respectively.…”

“…5 Physical properties of the polycrystalline thin films are determined by their texture, which gives rise to seeking ways to control the texture of a growing film. 4 Thin films usually have one of the crystallographic axes in the out-of-plane direction and no in-plane alignment. In this case, the preferred orientation is known as fiber texture.…”

“…Depending on the growth conditions, AlN can respond to the incident atoms by tilting its c axis toward the deposition direction. 4 Dellas and Harper proposed that the fiber axis of a growing film is tilted in off-normal angle sputtering conditions due to the low adatom mobility. 6 Materials with higher melting point typically have lower atom mobilities at low temperature ͑i.e., temperatures less than 1 3 of melting point͒ deposition conditions.…”

Characterization of radio-frequency sputtered AlN films by spectroscopic ellipsometry

“…4 AlN thin films have been prepared by many methods, including chemical vapor deposition (CVD), 5 molecular-beam epitaxy (MBE), 6 pulsed laser deposition, 7 and reactive sputtering. 8,9 Among them, radio frequency (RF) magnetron sputtering is a popular method because textured thin films can be obtained at low cost and low temperature.…”