Copper-based Self-assembled Diffusion Barrier Layer Technology Research

As the feature size of ICs shrinks, the thickness of the diffusion barrier in copper interconnect process is becoming thinner and thinner. The conventional Ta/TaN bilayer diffusion barrier becomes too thin to maintain enough reliability. One effective method to solve this problem is the introduction of self-forming barrier which is normally Cu alloys. After the deposition of Cu-Mn alloy or Cu-Al alloy, the films are then annealed at a certain temperature, and as a result, the layers are automatically separated into the seed layer, the stable phase layer and the diffusion barrier.According to a phase diagram, the formula, the preparation method, the process and service conditions of a material can be chosen and determined. Using the graphic method, a alloy phase diagram describes the relationship among alloy composition, the state of balance phase and external conditions (temperature,pressure and so on). The state, the formation of the existing phases and so on can be learned when a system is in balance at any temperature by the phase diagram.For the technology node of 45nm,32nm, the desired barrier thickness is different. To meet the demand for the diffusion barrier thickness for different technology nodes, annealing temperature and mole fraction of the element in the alloy's influence on the diffusion barrier thickness should be considered. Therefore, by the use of the data from the phase diagrams, along with the model illustrating the changes of the alloy layer after annealing, for different technology nodes, the range of mole fraction of the element in the alloy corresponding to different annealing temperatures are calculated in this thesis. After further discussions, specific values of annealing temperature and mole fraction of the element in the alloy are presented.In addition to annealing temperature and mole fraction of the element in the alloy, the time spent in annealing also has an effect on the barrier thickness. According to the logarithmic rate law which was proposed for the low-temperature oxidation, the barrier thickness will become thicker as the annealing time increases. Besides, by analyzing the model describing the internal and external oxidation, while using Cu-Mn alloy, if a small amount of oxygen is added into the annealing atmosphere, the interconnect resistivity will be lowered. These results are of great importance and are instructive for the set of parameters in copper interconnect process in ICs manufacturing.