Enhancement of electrical property and thermal stability of (Ba,Sr)TiO/sub 3/ thin films on Cu(Mg) bottom electrodes

The feasibility of using Cu (Mg) alloy films as bottom electrodes for (Ba,Sr) TiO/sub 3/ (BST) capacitors has been investigated for application of high-frequency devices at interconnect levels. When Cu was used as the bottom electrode of the BST capacitor, severe interdiffusion occurred between Cu and BST and resulted in serious oxidation after annealing in an oxygen ambient at elevated temperatures. BST/Cu(Mg) structure reduced the leakage current density down to 3.0 /spl times/ 10/sup -8/ A/cm/sup 2/ at 1 MV/cm and increased the breakdown filed up to 2.4 MV/cm from 0.4 MV/cm at 10/sup -6/ A/cm/sup 2/ compared to BST/Cu structure. The enhancing characteristics of the BST/Cu(Mg) structure are most likely due to the formation of a self-aligned MgO layer, which results in excellent diffusion barrier properties and electrical characteristics. In addition, the bias temperature stressing under an electric field of 2 MV/cm and temperatures between 100 and 200/spl deg/C was used to accelerate the Cu ion drift. The BST films using Cu(Mg) as electrodes are found to have lower Cu drift than those using Cu electrodes. Therefore, a self-aligned MgO layer could be a good Cu drift barrier layer for reliable ULSI interconnects.