Formation, oxidation, electronic, and electrical properties of copper silicides

Abstract

The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing-angle x-ray diffraction, scanning electron microscopy, and x-ray photoemission spectroscopy. Schottky-barrier-height measurements on n-type Si (100) have also been performed in the temperature range of 95–295 K with the use of a current-voltage technique. The results show that a metal-rich compound with a composition in the Cu3Si range forms at low temperatures (473 K). The electronic properties of the compound are dominated by the hybridization between the Cu(d) and Si(p) valence states. A direct consequence of this hybridization is the peculiar oxidation behavior of the compound surface; both Cu and Si have been found to oxidize at room temperature. The oxidation of Si in the silicide is enhanced as compared with the oxidation of the elemental single-crystalline Si surface. Upon annealing the oxidized surface, a solid state reaction takes place: Cu2O disappears and a thicker SiO2 layer grows, owing to the large difference in free energies of formation between SiO2 and Cu2O. The n-type barrier height of 0.79 eV for both the as-deposited metal and the metal-rich silicide phase decreases with increasing temperature with a coefficient close to the temperature coefficient of the indirect energy gap in Si. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge, independent of temperature.

Reaction of nanometer-sized Cu particles with a SiO2 substrate

“…Strongly bonded Cu may catalyze the Si-O bond breaking, since Cu also catalyzes the reverse reactions of Si-O formation. 13,14,[16][17][18] Metal evaporation as applied by others 9,21 may result in a weaker metal-support interaction 4 and, therefore, not result in a reaction between Cu and SiO 2 during UHV annealing. We note that also impurities on the sample surface or constituents of the residual gas may help to reduce SiO 2 .…”

“…13,14,16 Roomtemperature oxidation of Si is catalyzed by Cu 3 Si and a thick amorphous SiO 2 layer grows spontaneously beneath the Curich layer. 17,18 So the ease of regeneration of the annealed Cu/SiO 2 samples as described above can be understood from the oxidation behavior of a silicide and is another piece of evidence for the presence of Cu silicide after annealing in UHV.…”

“…The signals are measured while keeping the sample at the annealing temperature for 10-15 min. Cu becomes fully visible again in LEIS spectra after sputtering at room temperature, using approximately 10 16 He ϩ ions/cm 2 , indicating that Cu is present just below the surface of the sample after UHV annealing. RBS spectra before and after annealing up to 620°C are identical within experimental error.…”

Analysis of copper-rich precipitates in silicon: Chemical state, gettering, and impact on multicrystalline silicon solar cell material

“…5 Macroscopic studies on and models of the properties of copper silicides have also indicated a hybridization of the valence Cu and Si orbitals. 29,[57][58][59] The increased delocalization of Cu valence electrons can qualitatively explain the Cu-K absorption edge shift to higher energies: as they are photo-excited out of the atom, Cu 1s core electrons experience a greater Coulombic attraction with the Cu nucleus due to reduced electron screening, and thus require higher x-ray energies for photoionization.…”

Dependence of Microstructural Evolution of Nanoindented Cu/Si Thin Films on Annealing Temperature

“…12,13) Amongst all the face-centered cubic (fcc) materials, copper (Cu) tends to be one of the most commonly used for the coating of silicon substrates in the fabrication of modern electronic devices dues to its high chemical stability, low resistivity, good patterning ability, good reliability, ready availability, and low cost. 14,15) Various physical and chemical methods have been proposed for the fabrication of Cu/Si systems with coherent layers. [16][17][18][19] It is known that the bonding strength of the Cu/Si system is enhanced via the precipitation of copper silicide particles via a solid state reaction when the interface between the thin Cu film and the Si substrate is heated to a sufficient temperature.…”