Optical and structural properties of highly c-axis oriented aluminum nitride prepared by sputter-deposition in pure nitrogen

Nanocrystalline aluminum nitride films (70-1400 nn thick) were prepared by rf-magnetron sputtering from an Al-target at a substrate temperature of 540 K. For the first time, the influence of the pressure on the film propertie s was investigated for sputter-deposition in pure nitrogen-atmosphere. The pressure was varied in the range from 0.15 to 4.0 Pa. The deposition rate d ecreases monotonically from 0.35 to 0.17 nm/s with pressure. Films of 300 n m thickness show at 1 Pa nitrogen pressure a maximum of the crystallite siz e (in direction parallel to the film normal), which amounts to 30 nm. Highl y strained crystallites grow at pressures below 0.5 Pa. The films are (exce pted sputtering above 2 Pa) in general highly c-axis oriented. It is found that the crystallites are of a cylinder-like shape with axis orientation pa rallel to the film normal and a roughly constant length-to-diameter ratio o f 4. The optical properties static refractive index and optical Tauc gap de pend weakly on the pressure and are on average 2.0 and 5.0 eV, respectively . The bombardment of the growing AlN by energetic nitrogen neutrals origina ting from reflection at the target, which was simulated by TRIM.SP Monte-Ca rlo calculations, is suggested to be the general origin of the preferred c- axis growth of sputter-deposited films. (C) 2000 Elsevier Science B.V. All rights reserved.