Processing, characterisation and related application of magnetron sputtered aluminum nitride films

1 v. (various pagings) : ill. ; 30 cm.Aluminum nitride (AlN) thin films with different crystallographic structures were fabricated by radio frequency reactive magnetron sputtering technique. The film structure was characterized, and their physical properties, including the piezoelectric, dielectric and mechanical properties, were measured. Two aspects of information were attained. First, we gained the knowledge of the deposition condition dependence of the film structure, from which one can be able to control the film structure by appropriate selection of the preparation parameters. The second, we gained the knowledge of the structure dependence of the film properties. It was found that films of nearly amorphous (na-), polycrystalline (p-), texture (t-) and epitaxial (e-) structure can be obtained through appropriate settings of substrate temperature (Ts), RF power (Pw) and the selection of substrate material. Three substrate materials, i.e. Si(100), Pt(111)/Si(100) and single crystal Al₂O₃(00.l) were used in the study. All the deposition runs had a fixed target-to-substrate distance (D) of 10 cm, which was much larger than the mean free path (p) of the particles (= 1 cm) in the vacuum of 5 m Torr. Under such a large D/p ratio, the species collided frequently in the vacuum. Ts, and Pw have the effects of affecting the thermal and kinetic energies of the species. The influences of Ts and Pw compensate mutually with each other. Namely, the effects caused by the use of a low Ts can be compensated by the use of a higher Pw, or vice versa.When a low Ts, and a low Pw were used, the na-AlN structure was formed. This structure contains small and randomly oriented AlN grains. The formation of such a film structure was independent on the selection of the substrate material. The corresponding ranges of Ts and Pw were presented in a Ts-Pw diagram, and was denoted as the na-AlN region. The na-AlN structure was formed because at low Ts and Pw conditions, the species involved in the sputtering process were relatively immobile on the substrate surface. With the use of high Ts and Pw (denoted as the p-AlN region in the Ts-Pw diagram), p- film was formed which contained larger AlN crystallites. The orientation of the crystallites was relatively random. For further increase in Ts and Pw, t-A1N was formed if a Si(100) or a Pt(111)/Si(100) substrate was used. e-A1N film was formed if an Al₂O₃(00.1) substrate was used. The piezoelectric coefficient d'₃₃ of AlN films was measured by a laser interferometer. The true d'₃₃ of a film was correction for the clamping effect by the substrate. d'₃₃ of a na-AlN film was determined to be 0.28 pm V⁻¹. This result suggests that even a highly disordered AlN film could have detectable piezoelectric response. The range of d'₃₃ of the p-AlN films was found to lie in a broader range of 1.38-6.2 pm V⁻¹. The d'₃₃ value of a t-AlN film was 5.5 pm V⁻¹, which was close to the upper bound of the d'₃₃ of the p-AlN films. The dielectric properties of some selected AlN films were measured. The dielectric constant was found to be in the range of 9 - 13 in the frequency range of 10 kHz - 1 MHz. The hardnesses and elastic moduli of the AlN films deposited on Si(100) were investigated by nanoindentation method. Their values were found to vary with the film structure. A na-AlN film had the lowest hardness and elastic modulus, i.e. around 12 GPa and 170- 190 GPa, respectively. With the increase in the level of crystallinity, the films became less porous, and both the hardness and elastic modulus increased to a higher level. For a p-AlN film, the hardness and elastic modulus increased to 15 GPa and 220-240 GPa, respectively. For a t-AlN film, the hardness and elastic modulus were found to reach 21 GPa and 240-250 GPa, respectively.Department of Applied PhysicsM.Phil., Dept. of Applied Physics, The Hong Kong Polytechnic University, 2004