Ru thin films prepared by RF magnetron sputtering with Ru targets of different microstructures

Abstract

Ruthenium (Ru) exhibits excellent electrical properties at the nanoscale, and it can be used to replace Al and Cu as interconnect metals for nodes of 20 nm and below in the next generation of integrated circuits. Ru interconnects mainly exist in the form of films, and Ru targets are used as the key raw materials to produce these films. Establishing whether there is an inheritance relationship in terms of microstructure and electrical properties between these targets and the resultant films will determine whether these are important factors for improving the electrical properties of Ru films and will provide directional guidance for the preparation of Ru targets. In this work, Ru targets were prepared by vacuum hot pressing with two different Ru powders with different morphologies and particle sizes. Ru films were then deposited on SiO2/Si(100) substrates by RF magnetron sputtering at substrate temperatures ranging from room temperature (RT, about 25 °C) to 400 °C. The microstructures and electrical properties of the Ru targets and Ru films were investigated by high-resolution field-emission scanning electron microscopy, x ray diffraction, atomic force microscopy, four-probe resistivity measurements, and digital conductivity tests. The results showed that Ru targets with a more uniform microstructure had lower resistivity; furthermore, Ru films deposited by Ru targets with a more uniform microstructure were preferentially crystallized, and they also had a faster average deposition rate, a smaller average grain size, and lower surface roughness. However, no correlation was found between the crystal orientations of the Ru films and Ru targets.