Abstract
Interfacial reactions of ultrahigh-vacuum-deposited (UHV) Cu thin films on Si, Ge and on epitaxial Si-Ge layers on Si and Ge are reviewed. Both aligned and twinned epitaxial Cu thin films have been grown on (111)Si at room temperature. An interface compound, CuSi x , with x = 11.2-14at%, was observed to be present at the Cu/Si interface. (η″-Cu 3 Si was found to form in samples annealed at 200°C for 1 h. Preferentially oriented η′-Cu 3 Si is the only phase present in samples annealed at 200-800°C. In the samples annealed at or higher than 850°C, a mixture of η′-Cu 3 Si and η″-Cu 3 Si was found to be present. The effects of substrate cleaning and film thickness on the epitaxial growth of UHV deposited Cu thin films were found on (001)Si. In as-deposited samples, Cu films were found to grow preferentially along the [111] direction on atomically clean (2 × 1)(001)Si reconstructed surface and grow along the [001] direction on hydrogen terminated (001)Si. The Cu lattice is rotated by 45° relative to Si along the [001]Cu/[001]Si axis. The alignment of the Cu overlayer was found to improve with the distance from the Cu/Si interface. Epitaxial Cu and epitaxial ζ-Cu 5 Ge were found to form in as-deposited Cu/ epitaxial-Ge(e-Ge)/(111)Ge and Cu/e-Ge/(111)Si. On the other hand, textured Cu was found to form in the other systems. Polycrystalline ε1-Cu 3 Ge and ε1-Cu 3 (Si 1-x Ge x ) were the only phases formed in 150-500°C annealed Cu/Ge and (Cu/e-Ge/Si and Cu/Si-Ge alloys) systems, respectively. They were found to agglomerate at 550°C. The room-temperature oxidation of substrate in the presence of Cu 3 (Si 1-x Ge x ) was found only in the Cu/Si 0.7 Ge 0.3 system. From the sheet resistance measurement, ε1-Cu 3 Ge has the lowest resistivity of 7 μΩ-cm after the 400°C annealing. The electrical resistivity was found to decrease with the Ge content. © 2004 Elsevier Ltd. All rights reserved.