Growth of thin films with preferential crystallographic orientation by ion bombardment during deposition

Ion bombardment during the growth of a film may considerably influence the structure of this film. Often a preferred crystallographic orientation of the film grains is observed. As an example, NaCl-type crystals tend to grow in a preferred [111] direction normal to the film plane owing to surface energy effects in connection with close-packed structures. However, upon ion irradiation the alignment shifts towards [100]. The ions channel along this direction deep into the lattice which as a consequence suffers from less radiation damage and sputtering. Both effects are in competition with each other during film growth. The most important factor for preferential growth is the ratio of impinging ions to arriving atoms. When off-normal ion incidence is applied, the alignment of the crystals follows the ion beam line to a certain extent. When irradiation effects and surface energy effects are combined by off-normal bombardment at selected angles, an azimuthal order can be achieved in addition to the surface normal alignment. This may result in biaxially aligned films with the perspective of unique properties. The above-mentioned effects are discussed on the basis of results from X-ray diffraction measurements on titanium nitride films grown by metal evaporation under nitrogen or argon ion bombardment. ((orig.))