Electrical Properties of Giant‐Grain Copper Thin Films Formed by a Low Kinetic Energy Particle Process

Abstract

Formation of giant‐grain copper thin films on by a low‐kinetic energy particle process followed by thermal annealing has been investigated. When Cu films are grown on by the process under a sufficient amount of energy deposition, they exhibit almost perfect crystal orientation conversion from Cu(111) to Cu(100) upon thermal annealing. Such crystal orientation conversion is accompanied by the giant grain growth in the film as large as 100 μm. With regard to these phenomena, the effects of the ion flux density and of the ion bombardment energy have been studied. It was found that the crystal orientation conversion and the accompanying grain growth are governed by the total energy deposited to the as deposited film. The Cu film resistivity decreases when the giant grain growth occurs in the film due to the increase in the grain boundary scattering. At room temperature, the resistivity of the Cu film having giant grains is 1.76 μΩ · cm, almost equal to the bulk resistivity of 1.72 μΩ · cm. When the temperature is reduced to a low temperature of 12 K, the resistivity becomes as low as 18.3 nΩ · cm, which is almost one order of magnitude lower than that of the as deposited film also measured at 12 K (152 nΩ · cm). Furthermore, it is confirmed that the interconnects formed by giant‐grain Cu films can with‐stand from one to two orders of magnitude larger currents than Al‐Si‐Cu alloy interconnects, provided both interconnects exhibit the same electromigration lifetime. It is also shown that giant‐grain Cu interconnects exhibit longer lifetime than the Al‐Si‐Cu alloy interconnects by three to four orders of magnitude under the same current stress. These experimental results demonstrate that the giant‐grain Cu film is a very promising material to form low‐resistivity, high‐reliability interconnects for future subhalf micron ultralarge scale integrated circuits.