Pulsed Laser Deposition and Characterization of Novel Cu/TiN/Si(100) Heterostructures Grown VIA Domain Epitaxy

Abstract

Laser physical vapor deposition (LPVD) has been used to study the growth morphology of copper thin films on siliconi 100) substrates with epitaxially grown titanium nitride buffer layers. The epitaxial TiN film was grown on hydrogen-terminated Si substrate at 600°C. The Cu films were grown on TiN/Si at different substrate temperatures ranging from room temperature to 600°C in vacuum (∼10-7 torr) with a pulsed KrF excimer laser (τ = 248 nm, ι = 25 ns). The pulse repetition rates were 15 and 30 Hz. The X-ray diffraction (XRD) results indicate that below 200°C, the Cu film has a mosaic spread of (001) textures of about 2.3° and that a small fraction (0.05 ) is of (111) textures. But above 200°C there is only (001) textures Cu of about 0.42° to 0.40° depending on the substrate temperature (200° - 600°C). The Rutherford backscattering (RBS) spectra show that the TiN has a yield (xmin) of 13.5 % whereas that for Cu is 70 %. A detail high resolution transmission electron microscopy (HRTEM) was performed to reveal the growth morphology of Cu films with substrate temperature. It was observed that at 15 Hz, Cu grows three-dimensionally on TiN with the island sizes ranging from 0.3–1.5 μm depending upon the substrate temperature. All of these islands grow epitaxially on TiN giving rise to Cu ║ TiN ║ Si. At 30 Hz, there is a uniform growth of epitaxial cube-on-cube Cu film on TiN/Si. The Cu/TiN and TiN/Si interfaces are quite abrupt with absolutely no indication of interfacial reactions between them. Moire fringe spacings suggest that both TiN and Cu unit cells are completely relaxed. Although there exist a large lattice misfit between Cu and TiN (15.8%) and as well as between TiN and Si (24.6%), it has been possible to grow epitaxial Cu/TiN/Si(100) heterostructures by means of domain epitaxial growth. In this case, there are 4-to-3 match in unit cells for TiN/Si structure and 7-to-6 match for Cu/TiN structure giving rise to remaining lattice misfits of only 4.0% and 0.6% respectively.