ENHANCED ADHESION OF COPPER TO DIELECTRICS VIA TITANIUM AND CHROMIUM ADDITIONS AND SACRIFICIAL REACTIONS

Ti and Cr as both interposed layers and alloying components were found to enhance copper adhesion to dielectrics. Films deposited on SiO2, phosphosilicate glass (PSG) and boromphosphosilicate glass (BPSG) were annealed in 95%Ar-5%H-2 over the temperature range 400-600 degrees C. The force required to separate films from substrates was measured by scratch testing. Optical and scanning electron microscopies provided detection of substrate exposure. In the Cu/Ti and Cu/Cr bilayer systems the force decreases with temperature on all substrates, generally exhibiting better adhesion on SiO, than on PSG or BPSG. In the Cu(Ti) and Cu(Cr) alloy systems the force increases with temperature with less systematic difference among the three substrates. These results correlate well with tape testing. Ti and Cr segregate out of the Cu layer and react both with the dielectrics and with the ambient gases, as observed by Rutherford backscattering and secondary ion mass spectroscopy. These reactions appear to improve adhesion; however, only a small amount of this reaction is required for the enhancement to occur. We surmise that stress in the copper and/or voiding at the Cu-dielectric interface may play a role as well. We observe a correlation between adhesion and the degree of Cu texturing.