Enlarged Lateral Grain Size and Reduced Surface Roughness in Metallic Thin Films Obtained by Thermal Annealing under Ultra-high Vacuum

摘要

The effect of thermal annealing under ultra-high vacuum on the metallurgical microstructure of (111)-textured face-centered cubic (FCC) metal thin films was investigated. The surface morphology of 500-A-thick metal films drastically changes with increasing annealing temperature. Regardless of the kind of metal, the morphological changes can be classified into four stages, when the annealing temperature, T_(IR), is normalized by the respective melting point of the metals, T_M. In stage I, 0.15 <= T_(IR)/T_M < 0.3, the surface roughness, R_a, of metal films decreases to approx 3 A. In stage II, 0.3 <= T_(IR)/T_M <= 0.35, remarkable grain growth occurs, and the lateral grain diameter exceeds 1000 A. Small (approx 200 A) crystals appear on the large grains in the stage II', 0.35 < T_(IR)/T_M <= 0.45, and they grow large and coarsen the R_a in stage III, 0.45 < T_(IR)/T_M. We conclude that ultra-high vacuum annealing in stage II is effective in realizing large lateral grain size with small surface roughness in FCC metal films.