(Sn,Al)Ox Films Grown by Atomic Layer Deposition

(Sn,Al)O-x composite films with various aluminum (Al) to tin (Sn) ratios were deposited using an atomic layer deposition technique. The chemisorption behavior of cyclic amide of tin(1) and trimethylaluminum were analyzed by Rutherford backscattering spectroscopy, Both precursors showed retarded and enhanced chemisorption on Al2O3 and SnO2 surfaces, respectively. The films show highly anisotropic electrical conductivity, i.e., much higher resistivity in the direction through the film than parallel to the surface of the film. The cause of the anisotropy was investigated by cross-sectional transmission electron microscopy, which showed a nanolaminate structure of crystalline SnO2 grains separated by thin, amaphous Al2O3 monolayers. When the Al concentration was higher than similar to 35 atom %, the composite films became amorphous, and the vertical and lateral direction resistivity values converged toward one value. By properly choosing the ratio of SnO2 and Al2O3 subcycles, controlled adjustment of film electrical resistivity over more than 15 orders of magnitude was successfully demonstrated.