Phosphosilicate glass passivation for ULSI Cu metallization

Phosphosilicate glass (PSG) passivation for Cu metallization is proposed, and the Cu diffusion rate into Si substrates through various oxide structures is measured quantitatively. Cu diffusion is suppressed effectively by the PSG passivation resulting in reduction of the diffused Cu atoms to about an order of magnitude less than when passivated by nondoped SiO₂ films. The passivation is effective when the annealing temperature is less than 600°C. The apparent activation energy of Cu diffusion for the nondoped SiO₂/Si substrate and PSG/nondoped SiO₂/Si is 1.2 and 1.6 eV, respectively. However, most of the diffused Cu precipitates near the oxide/Si substrate interface and the amount of the diffused Cu is comparable to the limit for ordinary device contamination. Thus, further improvement or optimization of the passivation layer structure is desired.