The Effect Of Metal Substrates On The Oxidation Reliability Of Electrodeposited Copper Interconnect Layers

In the 21st century the semiconductor devices have been developed rapidly. With the increasing integration of the device, the device feature size is required to decrease rapidly, which means higher demands for the interconnect materials inside the device. Because of excellent electrical conductivity and thermal conductivity copper and its alloys have become important interconnect material, widely used in large scale integrated circuit chip, microelectronic packaging, MEMS, solar cells and other devices. Despite these advantages, copper has a high affinity of oxygen, which means in placing and packaging heating process, the surface is prone to oxidation. The resistance of oxidation interconnects wires increases dramatically, resulting in device performance instability or even damage. And a too thick oxide film will reduce the lead frame and package resin bond strength between their interface, resulting in the package cracking and delamination. Therefore, to study and solve the oxidation of the copper layer for improved device reliability failures have a crucial role. In this paper, the effect of metal substrates having on electrodeposition of copper layer and its antioxidant reliability were investigated. Because the base substrate had significant influence on the morphology and the structure of electrodeposited copper layer, which was directly related to the antioxidant properties of the copper layer. In this experiment, three types of metals substrates were used as research materials. The electrodeposition method was used to form copper layer on their surfaces. It was analyzed and compared the diversity of copper interconnects layers morphology and structure that grows on different types of substrates. Then we investigated the effect that the diversity having on copper oxide microstructure, oxide film thickness and oxide film / resin interface bond strength Influence. And we investigated copper oxidation mechanism from the perspective of the oxidation kinetics.The results showed that in the C194 alloy substrate and pure nickel substrate were polycrystalline substrates. The morphology of copper layer grown on which was influenced by the substrate. The plating layer was composed of large particle size grains and loose structure. Ni-P alloy substrate was amorphous state. The electrodeposition copper layer on it did not affected by the of epitaxial growth effect. At 25oC, under the conditions of current density 2A/dm~2, the plating layer presented Cu (111) growth orientation, which was close-packed surface of fcc crystal. The morphology of oxidation product could also be observed to have difference. Oxidation product on C194 substrate and nickel alloy substrate were composed of large particles which were sparsely arranged. Oxidation product on nickel-phosphorus alloy substrate on the substrate was composed of fine particles, which were densely arranged. X-ray diffraction analysis (XRD) was used to detect the oxides component and oxide content variation as a function of oxidation temperature. The oxide content of copper deposition on Ni substrate increased rapidly with the oxidation temperature increasing, while the oxide content of copper deposition on nickel-phosphorous alloy substrate increased mildly as temperature rising high.The oxide film thickness was measured by chronoamperometry. The experimental results showed that the oxide film thickness and the oxide film / resin interface bond strength were not proportional. The thickness of copper oxide film on C194 alloy substrate was larger than that of Ni-P substrate, but its bond strength was better. Oxidation kinetics results showed that oxidation mechanisms of copper on these two types substrate were similar. The oxide thickness growth followed logarithmic law. The Oxygen molecules and copper ions exchanged rapidly through the defects in oxide film. The oxidation reaction was completed in the form of grain boundary diffusion. Copper oxide film on C194 substrate was less dense than that on Ni-P structure, so its oxidation process was more rapid. On the other hand, the diffusion activation energy of copper oxide on C194 substrate was lower than that on nickel-phosphorus substrate, which meant that the electrodeposition copper layer on C194 substrate only had to overcome a lower energy barrier when the oxidation happened.