Formation of giant-grain copper interconnects by a low-energy ion bombardment process for high-speed ULSIs

Abstract

When Cu films are grown on SiO 2 by a low-energy ion bombardment process under a sufficient energy deposition, the film exhibits almost perfect crystal orientation conversion from Cu(111) to Cu(200) upon post-metallization thermal annealing, which is accompanied by the growth of giant grains as large as several hundred micrometers. The room-temperature resistivity of such giant-grain Cu films is 1.76 μΩ cm, which is almost the same as the bulk value (1.72 μΩ cm). The giant-grain Cu interconnects exhibit an electromigration resistance three orders of magnitude larger than Al-alloy interconnects, when the life-test data are extrapolated to room temperature. We have shown that the employment of a non-oxidizing ambient, such as N 2 ambient, is essential for electromigration life-test of Cu interconnects, because Cu is easily oxidized in air. We have investigated the properties of Ta thin films as a diffusion barrier between Cu films and Si substrates using p-n junction diodes. It is shown that a 10 nm thick Ta film works as a effective barrier for temperatures up to 500 °C.