Effects of thermal treatment on structures of Cu/atomic-layer-deposited TaN films/Si stacks

Atomic layer deposition (ALD) TaN films are designed as diffusion barriers for Cu metallization of silicon devices. In a previous paper, we characterized the compositions and structures of ultrathin ALD TaN films. In this study, the effects of various thermal processes on the characteristics of Cu/ALD TaN/Si stacks are investigated by various analytical techniques. The results indicate that, for the as-received Cu/ALD TaN/Si samples (G1 set samples), thermal treatment at a temperature higher than 500 °C results in formation of the intermetallic compound Cu3Si on the surface. It is interesting to note that the amount of copper silicide on the surface increases with the ALD TaN thickness, as long as the later is less than 10 nm. No Cu3Si is detected after the same thermal process in similar stacks, when the top-layer Cu was deposited on pre-annealed ALD TaN/Si samples (G2 set samples). Cu dewetting occurs after thermally treating the Cu/ALD TaN/Si stacks for both G1 set and G2 set samples. Analysis indicates that impurities play an important role on the thermal behaviors of G1 and G2 stacks.