Electrodeposition of CoWP film: V. Structural and morphological characterisations

Abstract

CoWP films were electrochemically deposited on copper-coated silicon wafers from citrate electrolytes containing cobalt sulphate, sodium tungstate and sodium hypophosphite under various deposition conditions and characterisations of the films were carried out using various instrumental techniques. Composition analyses using XPS showed that the surfaces of the films contained large amounts of oxides and hydroxide of tungsten and cobalt, respectively. An AES depth-profile, however, revealed that the bulk of the films predominantly consisted of cobalt, tungsten and phosphorus. Microstructural analyses using XRD showed that, depending on the composition and/or deposition conditions, CoWP films could be amorphous, polycrystalline and crystalline with a strong preferred orientation. Amorphous films were obtained when deposited at higher applied potential and current density or the films contained high amount of phosphorus and/or tungsten, while films deposited by very low applied potential and current density were crystalline with a preferred orientation of [0 0 2] of hexagonal cobalt. SEM images showed that the films deposited from neutral or acidic baths at room temperature had typical spherical nodular structures, while the films deposited from basic solution or at elevated temperature had needle-like crystallites. The crystalline films were much rougher than the amorphous films.