Electrochemical deposition and characterization of copper oxide films

Abstract

The trend to smaller chip sizes and increased circuit densities demand for high-performance materials. Copper, which is commonly used in integrated circuits as conductive component, is susceptible regarding chemical and thermal stress. Electrodeposited Cu2O has shown to improve the chemical and thermal stress resistance of the circuits’ conductive surface. Cu2O thin films were electrodeposited on copper-metalized silicon wafers from an alkaline Cu(II) lactate solution in a thermostat-controlled beaker. The main purpose of this study was to investigate the electrodeposition of Cu2O films and their stability towards H2S exposure and elevated temperatures as well as photo-enhanced electrodeposition. To study the influence of H2S exposure on Cu2O, experiments were performed in a desiccator setup and in a weathering chamber, respectively. Energy dispersive X-ray spectroscopy was used to investigate the dependence of the susceptibility of the surface towards H2S on the layer thickness of Cu2O. Cu2O was also examined with respect to its thermal properties. Therefore, continuous XRD measurements at elevated temperatures were performed and changes in the resulting spectra were observed. Electrochemically deposited Cu2O prevented the formation of a mixed copper oxide at 150°C and 250°C. Formation of CuO was only observed at 350°C. To obtain information of a surface’s topography, samples were scanned with a stylus profilometer. The results indicate a linear correlation of film growth and deposition time. Furthermore, a relationship between surface roughness and film thickness was found. By depositing Cu2O using a square wave current, rough layers were deposited leading to improved adhesion properties. Adhesion tests were performed by tape tests. Photo-assisted electrodeposition of Cu2O was performed. Irradiating blue light from a LED onto the working electrode lead to changes in layer thickness, increasing the average current in a potentiostatic electrodeposition.