Sputter-deposited Mo and reactively sputter-deposited Mo-N films as barrier layers against Cu diffusion

This work studied the barrier capability of sputter-deposited Mo and reactively sputter-deposited Mo-N layers against Cu diffusion in a device structure of Cu/barrier/p +n junction diodes. With a 500 Å thick Mo film as barrier layer, the Cu/Mo/p +n junction diodes were capable of withstanding 30 min of thermal annealing at temperatures up to 500°C without causing degradation to the devices electrical characteristics. The incorporation of nitrogen in the Mo layer improved the barrier capability of the metal layer. In particular, the Mo-N films sputterdeposited in a gas mixture of Ar and N 2 with Ar/N 2 flow rates of 24/8 to 24/12 sccm were found to possess the best barrier capability. With a 500 Å thick Mo-N barrier layer, the thermal stability of Cu/Mo-N/p +n junction diodes were found to reach 600°C. At temperatures exceeding the thermal stability limit, we presumed that the failure of Cu/barrier/p +n junction diodes arose from two mechanisms: the grain boundary diffusion for the Mo film and the Mo-N films deposited with small N 2 flow rates, and the defects diffusion for the Mo-N barriers deposited with large N 2 flow rates. For the Mo-N films deposited in a gas mixture of medium nitrogen content (e.g. N 2 flow rate of 8 to 12 sccm), both of the failure mechanisms might exist simultaneously.