Copper-Carbon Alloy Films by Methane Beam Assisted Epitaxial Copper Deposition

Copper-carbon alloy films containing between 7 and 40 at.% carbon, as measured with 6.2 MeV He++ scattering, were deposited by ion beam assisted deposition (IBAD) on pure epitaxial Cu(100) films on Si(100) substrates. The IBAD process involved simultaneous deposition of evaporated copper (0.3 to 2.0 nm/s) and bombardment with 400 eV ions (340 fuA/cm2 on target) from a Kaufman ion source fed with methane. Transmission electron microscopy (TEM) showed that an IBAD layer with 15 at.%C was epitaxial with the underlying pure Cu(100) layer. X-ray diffraction (XRD) indicated that the IBAD films were epitaxial at low carbon concentration but polycrystalline at high concentration. The small range of carbon ions in copper and the evidence of sputtering suggest that this loss of epitaxy resulted from increased surface carbon interfering with epitaxy. Although carbon and copper are immiscible, TEM and XRD have revealed no evidence of carbon precipitation, indicating that the carbon may be in solution and that such IBAD layers may be suitable for diamond formation by laser annealing.