THERMAL-STABILITY OF COPPER SILICIDE PASSIVATION LAYERS IN COPPER-BASED MULTILEVEL INTERCONNECTS

Copper thin films were exposed to a dilute silane mixture at temperatu res in the range of 190-363 degrees C. The resulting silicide surface layers were characterized by four-point probe, Rutherford backscatteri ng spectrometry, and x-ray diffraction. A definitive stability regime is observed in which progressively higher copper content phases exist with increasing temperature. Cu3Si, formed in silane, on annealing con verts to Cu5Si and eventually to no silicide layer by a silicon diffus ion reaction that in an inert ambient drives silicon into underlying c opper to form a solid solution. In oxidizing ambients, a similar pheno menon occurs but now silicon also diffuses to surfaces where it oxidiz es to form a self-passivating SiO2 layer on surface. These results hav e important implications governing integration of copper silicide as a passivation layer and silicon hydride based dielectric deposition in copper-based multilevel interconnect in ultralarge scale integration. (C) 1998 American Institute of Physics.