Dependence of Cu∕Ta–N∕Ta Metallization Stability on the Characteristics of Low Dielectric Constant Materials

In this work, stability of the Cu/Ta-N/Ta/low-k material multilayers deposited on Si substrate was explored. The as-deposited Ta-N diffusion barriers are amorphous TaNx (x ~ 0.5) or polycrystalline TaN, whereas low-k materials include fluorinated silicate glass (FSG) and organosilicate glass (OSG). The thermal stability of the multilayers was assessed by annealing in vacuum at 400DGC for 30 or 60 min. After annealing, bubblelike topography was observed on the surfaces of the Cu/Ta-N/Ta multilayers deposited on FSG but not seen for the multilayers deposited on OSG. In addition, the blister size of samples with TaN, barrier was larger than that of samples with TaN barrier. The bubbles expanded in size with increasing duration of thermal annealing, especially for the samples with TaN, barriers. Poor adhesion between the annealed Cu/Ta-N/Ta multilayers and FSG was revealed by a tape test. Meanwhile, the test showed that the Cu/Ta-N/Ta multilayers deposited on OSG possess superior adhesion strength. The result can be attributed to the serious outgassing of FSG. The connection between the variation of sheet resistances and the interactions in the Cu/Ta-N/Ta/dielectrics multilayer structures upon annealing is discussed.