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 i measured quantitatively. Cudiffusion is suppressed effectively by the PSG passivation resulting in reduction of the diffused Cu atoms to about an order of magnitude l ss than when passivated by nondoped SiO., films. The passivation is effective when the annealing temperature is less than 600 ~ The apparent activation energy of Cu diffusion for the nondoped SiO2/Si substrate and PSG/nondoped SiO~/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. Highly packed, low resistivity multilevel interconnection is an important technologs ' for achieving higher speed and higher packing density ULSIs. Mctallization delay time al-ready has reached to about one-fifth of the total delay time, and the ratio increases ignificantly in deep submicron level ULSIs. ' In addition, A1 based fine metallization suf