Columnar Grain Structure in Cobalt Films Evaporated Obliquely at Low Substrate Temperatures

Abstract

We investigated the columnar grain structure in cobalt films evaporated obliquely at a low substrate temperature. The substrate temperature TS was varied from 113 to 313 K. The incidence angle was 60°, and the pressure during evaporation was 4.0 ×10-3 Pa. In the TS range of 230–270 K, the tops of the columnar grains exhibited the {0001} crystal habit and their bundling was formed, but at a TS below 220 K, the crystal habit disappeared and the bundling diminished. Furthermore, at a high pressure of 0.02 Pa obtained by closing the main valve halfway during evaporation, the bundling was also formed at a TS below 220 K, which indicates the exhibition of crystal habit. These results support our assertion that there exists a crystallographic contribution to the bundle formation through the crystal habit. The analysis of residual gas suggests that the disappearance and reappearance of the crystal habit at a TS below 220 K are due to contamination by H2O and N2 molecules, respectively.