Self-aligned passivated copper interconnects: a novel technique for making interconnections in ultra large scale integration device applications

We have developed a technique to grow self-aligned epitaxial Cu/MgO films on Si (100) using a Pulsed Laser Deposition Method. In this method we deposit a uniform film of Cu/Mg (5-7%) alloy over Si (100) at room temperature using TiN as an intermediate buffer layer. As a result of HRTEM (with spatial resolution of 0.18 nm) and STEM-Z investigations we observed that when this film is annealed at 500?C (in a controlled oxygen environment), in less than 30 minutes time, all the Mg segregates at the top and at the bottom surface of Cu. This is understood to be the consequence of lower surface energy of Mg. At 500?C Mg is quite sensitive to oxygen and a thin layer of MgO is immediately formed at the top surface, we also observed a thin layer of MgO at the Cu/TiN interface. Thickness of the upper MgO layer was found to be 15 nm while that of lower layer was 10 nm. MgO underneath layer acts as a diffusion barrier and inhibits the diffusion of Cu in the system. Upper MgO layer acts as a passivating layer and improves the quality of copper against oxidation. Electrical resistivity measurements (in the temperature range 12-300 K) showed MgO/Cu/MgO/TiN/Si (100) sample to be highly conducting. We also observed that the resistivity of the system is insensitive to ambient oxygen environment. Self-aligned MgO (100) layer also provides a means to grow several interesting materials over it. This technique can be used to integrate high temperature superconductors like YBa2Cu3O7 with silicon chip.