Development of alternative diffusion barriers for advanced copper interconnects.

摘要

The advance in silicon semiconductor processing has driven the minimum feature size towards 32 nm node. Copper has replaced Al as the dominant interconnect metal owing to its lower resistivity and better electromigration resistance. The diffusion of Cu into dielectrics or Si results in deteriorating device performance. To avoid copper diffusion, an effective barrier layer needs to be integrated to protect the device. Ta/TaN bilayer liner is currently used for Cu damascene process. As conventional electrodeposition of Cu requires a sputter deposited Cu seed layer, the continual shrinking in the minimum metal pitch width and increasing high aspect ratio will bring difficulty in conformal step coverage. This work firstly focused on investigating new possible liner replacement for Ta in order to achieve direct copper electrodeposition, and then studied on other possible nitride barrier candidates for Cu metallization.;As a liner material for direct copper electroplating with excellent conformity and high quality copper texture, the diffusion barrier properties of 5 nm iridium thin films for Cu metallization on Si were examined. To avoid iridium silicidation with the underlying Si and to enhance barrier properties against copper diffusion, the Ir/TaN bilayer approach was also studied. As the failure temperature for 5 nm iridium barrier was 400°C, the addition of TaN layer strongly improved the barrier performance. The utilization of Pd as a catalyst for Cu electroless deposition along with TaN to form a bilayer barrier was also investigated. The Pd/TaN bilayer structure was shown to prevent copper diffusion up to 550°C for 1 h.;Ternary refractory metal nitride W-B-N thin films were also studied as a candidate diffusion barrier for Cu metallization on Si. W-B-N thin films were amorphous with low resistivity ranging from 159.92 to 240.4 muOcm. The W-B-N thin films deposited at 5% N2 flow ratio can block Cu diffusion after 500°C annealing for 1 h. As one of the interesting refractory metal nitrides for Cu diffusion barrier application, the comparative study between ZrN and Zr-Ge-N thin films as diffusion barriers was also examined.