CHARACTERIZING FILM QUALITY AND ELECTROMIGRATION RESISTANCE OF GIANT-GRAIN COPPER INTERCONNECTS

The performance of copper interconnects formed by the low-kinetic-ener gy ion bombardment process has been investigated. The copper films for med on SiO2 by this technology under a sufficient amount of ion energy deposition exhibit perfect orientation conversion from Cu (111) to Cu (100) upon post-metallization thermal annealing. We have discovered s uch crystal orientation conversion is always accompanied by a giant-gr ain growth as large as 100 mum. The copper film resistivity decreases due to the decrease in the grain boundary scattering, when the giant-g rain growth occurs in the film. The resistivity of giant-grain copper film at a room temperature is 1.76 muOMEGAcm which is almost equal to the bulk resistivity of copper. Furthermore, a new-accelerated electro migration life-test method has been developed to evaluate copper inter connects having large electromigration resistance within a very short period of test time. The essence of the new method is the acceleration by a large-current-stress of more than 10(7) A/cm2 and to utilize the self heating of test interconnect for giving temperature stress. In o rder to avoid uncontrollable thermal runaway and resultant interconnec t melting, we adopted a very efficient cooling system that immediately removes Joule heat and keeps the interconnect temperature constant. A s a result, copper interconnects formed by the low-kinetic-energy ion bombardment process exhibit three orders of magnitude longer lifetime at 300 K than Al alloy interconnects.