Forming microstructures by controlling the accumulation and discharge of Al atoms by electromigration

We present a mechanism for controlling the accumulation and discharge of Al atoms using electromigration, by which long thin Al wires of lengths up to 336μm and diameters ranging from 0.8 to 4μm were fabricated. The experimental samples were Al lines formed on a TiN layer and covered with a SiO₂ passivation layer. A slit in the Al film and a hole through the oxide or through the oxide and the Al film at the anode end of the line were used to control the accumulation and discharge processes. It was found that the position of the bottom of the hole, which was either at the SiO2/Al or Al/TiN interface, significantly affected these processes. A hole introduced down to the Al/TiN interface prevented cracks from forming in the line by relieving the compressive stress caused by accumulating atoms, and helped to extend the lifetime of the line. Guidelines for effectively controlling the accumulation and discharge of Al atoms were drawn, and based on these guidelines, other Al microstructures requiring the accumulation of a large number of atoms were fabricated after several tens of minutes of current supply.