Electrochemical Deposition of Nanocrystalline Copper and Copper-Based Composite Films
Free-standing nanocrystalline copper-based composite and particle-free copper films were produced by direct- and pulse-current plating. Nanosize 50-nm Al2O3 or 5-nm diamond particles were codeposited into a copper matrix prepared on a rotating disk electrode (RDE). The electrolytes contained CuSO4.5H2O (0.25 M), H2SO4 (0.56 M or 1.5 M), 50-nm Al2O3 (12.5 g/L or 1.0 g/L) or 5-nm diamond (0.5 g/L) particles, and gelatine (0.1 g/L, 0.05 g/L, or 0.02 g/L). The deposition was carried out at room temperature. The RDE was rotated at 1800 rpm for high-alumina particle baths (12.5 g/L) and 1000 rpm for low-alumina particle (1.0 g/L), diamond particle (0.5 g/L), and particle-free baths. The free-standing composite and copper films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), micro hardness tester, and transmission electron microscopy (TEM). Grain size and crystal texture were obtained by XRD measurement. SEM gave information on surface morphology and composition of films. The hardness of nanocrystalline materials was measured by micro hardness tester. TEM was used to confirm the presence of nanocrystalline copper grains. The uncompensated potential became more cathodic with increasing current density in pulse-current plating. The current efficiency was in the range of 0.93 ¨C 1.09 for both direct- and pulse-current plating. Gelatine concentration, the presence of nanosize dispersoids, and pH have no significant effect on electrode potential and current efficiency. Grain size decreased with increasing current density for particle-free copper and most of the composite films by direct- and pulse-current plating. The microhardness of nanocrystalline materials was increased by decreasing grain size for most of the particle-free copper and composite films. The existence of high-angle grain boundaries in nanocrystalline films resulted in negative Hall-Petch slopes. The presence of low concentration of alumina or diamond particles had no effect on grain size and microhardness. The pH had no obvious influence on grain size, microhardness, and alumina content in composite films. Random crystal texture is observed for Cu-Al2O3 composite and particle-free copper films and the (111) preferred texture for Cu-diamond composite films. The (100) preferred substrate orientation had no effect on deposit texture. The current density for both direct- and pulse-current plating had no significant effect on material texture. The presence of particles has no significant influence on nanocrystalline texture. Surface morphology varied for films made under different bath conditions. High gelatine concentration resulted in low-particle impregnation. Films made using 0.1 g/L gelatine resulted in spherical particles with grain size of 64 nm and porous surface. Films made using 0.02 g/L gelatine resulted in smooth surface with smaller grains of 40 nm. Films with high-alumina particle embedding, for example sample 7/9-1, resulted in porous and dark surface. High-alumina particle concentration (12.5 g/L) with 0.02 g/L gelatine in the deposition baths resulted in high-alumina content (0.11 wt% - 2.76 wt%) in composite films. The higher current density (297 mA/cm2) resulted in the lower alumina particle (0.076 wt%) embedding rate for the same bath parameter setting. The presence of both Al and O was found in copper-alumina composites and C element (diamond) was detected in copper-diamond composite films by EDS.
Advisor:Peter S. Fedkiw; Carl Koch; John Van Zanten
School Location:USA - North Carolina
Source Type:Master's Thesis
Date of Publication:01/14/2002