Influence of argon pressure on texture and microstructure of cobalt films produced by Dc-sputtering

Background and Objectives: The development of methods of textured Co film formation is of practical interest in the field of creating media with perpendicular recording of information or lateral spin-valve structures. Despite a rather wide study of the growth conditions effects on the microcrystalline structure of sputtered cobalt films, the possibility of changing the texture and microstructure via a change of the gas pressure has not been discussed. The purpose of this study is to show that for dc-sputtering the decrease of argon pressure P from 1 Pa to 0.13–0.09 Pa leads to the radical change in the microcrystalline structure of Co films. Materials and Methods: Textured cobalt films were dc-sputtered on SiO$_2$/Si substrates at 0.13–0.09 $\leq$ P $\leq$1 Pa and room temperature without substrate bias. The microcrystalline structure of the films was studied using the X-ray diffraction and the scanning electron microscopy techniques. Results: At P $\approx$ 1–0.22 Pa the cobalt films are formed with mixed crystalline phase: hexagonal close-packed (hcp) with (002) texture and face-centered cubic (fcc) with (111) texture and columnar microstructure. The reduction of the pressure to P $\approx$ 0.13–0.09 Pa (collision-free movement of sputtered atom from to produce the target to the substrate) leads to the formation of fcc Co films with (200) texture and nonuniform microstructure: at d<d$_c$ film shows the “quasi-homogeneous” microstructure and at d>dc microstructure becomes “quasi-columnar”. Decreasing P to the level 0.13–0.09 Pa is a technologically simple way of formation of cobalt films with fcc crystalline structure and (200) texture at room substrate temperature. Co(200) films with fcc crystalline structure can be applied in the field of creating an orienting underlayer to produce multilayered structures with perpendicular magnetic anisotropy or lateral spin-valve structures based on cobalt.