Interfacial mechanism studies of electroless plated Cu films on a-Ta:N layers catalyzed by PIII

Abstract

This study evaluated the interface reaction and crystallography of the electroless plated copper film (∼0.2 μm thick) catalyzed by plasma immersion ion implanted (PIII) Pd on the 150-Å-thick amorphous tantalum nitride (a-Ta:N) barrier layer. The copper plated specimens were annealed at various temperatures in an ambient atmosphere of 90% nitrogen + 10% hydrogen mixed gases. Sheet resistivity, Auger electron spectroscopy (AES) analyses showed that the PIII Pd atoms were diffused into the copper layer from the interface of a-Ta:N and copper layers after 500 °C annealing for 1 h. Results based on x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed a phase transformation from a-Ta:N into crystallized Ta2N phase at annealing. The Cu(111) texture was strengthened at 300 °C annealing for 1 h because of the relaxation of the residual stress and recovery of the copper film. The texture was reduced at the 500 °C annealing for 1 h because of the copper grain growth. The adhesion strength of copper films on a-Ta:N barrier layer was enhanced by the annealing because of the interdiffusion of copper layer, Pd clusters and a-Ta:N barrier layer. The annealing temperatures lower than 300 °C help to reduce the electric resistivity of copper film, to strengthen the Cu(111) preferred orientation, and to enhance the adhesion strength of copper films on a-Ta:N layer. However, the specimen annealed at 500 °C manifested the diffusion of Pd atoms into the copper film and resulted in a significant increase of the electric resistivity of copper film.