Structural and elastic characterization of Cu-implanted SiO2 films on Si(100) substrates

Abstract

Cu-implanted SiO2 films on Si(100) have been studied and compared to unimplanted SiO2 on Si(100) using x-ray methods, transmission electron microscopy, Rutherford backscattering, and Brillouin spectroscopy. The x-ray results indicate the preferred orientation of Cu {111} planes parallel to the Si substrate surface without any directional orientation for Cu-implanted SiO2/Si(100) and for Cu-implanted and annealed SiO2/Si(100). In the latter case, transmission electron microscopy reveals the presence of spherical nanocrystallites with an average size of ~2.5 nm. Rutherford backscattering shows that these crystallites (and the Cu in the as-implanted film) are largely confined to depths of 0.4−1.2 µm below the film surface. Brillouin spectra contain peaks due to surface, film-guided and bulk acoustic modes. Surface (longitudinal) acoustic wave velocities for the implanted films were ~7% lower (~2% higher) than for unimplanted SiO2/Si(100). Elastic constants were estimated from the acoustic wave velocities and film densities. C11 (C44) for the implanted films was ~10% higher (lower) than that for the unimplanted film. The differences in acoustic velocities and elastic moduli are ascribed to implantation-induced compaction and/or the presence of Cu in the SiO2 film.