Amorphouslike chemical vapor deposited tungsten diffusion barrier for copper metallization and effects of nitrogen addition

In this article, we propose an amorphouslike chemical vapor deposited tungsten (CVD-W) thin film as a diffusion barrier for copper metallization. Experimental results gave no evidence of interdiffusion and structural change for Cu/amorphouslike CVD-W/Si samples annealed up to 675 °C for 30 min in N2. At higher temperatures (700 °C), Cu penetration results in the formation of η′′-Cu3Si precipitates at the CVD-W/Si interface. This is due to the crystallization of the amorphouslike CVD-W film above 650 °C, rendering the grain-boundary structure and, hence, fast pathways for Cu diffusion. The Cu/amorphouslike CVD-W/p+n diodes, thus, sustain large increases in reverse leakage current. In addition, the effects of nitrogen addition by using an in situ nitridation on the amorphouslike CVD-W film are also discussed. The effectiveness of the nitrided barrier is attributed to the blocking of the grain boundaries in the tungsten film by nitrogen atoms. This slows down Cu diffusion significantly. Physical and chemical analyses indicate that interfaces in the Cu/WNx/W/Si multilayer maintain their integrity while the annealing is carried out at 750 °C. Moreover, the reverse leakage current densities of Cu/WNx/W/p+n diodes remain at 10−7 A/cm2 after 725 °C annealing.