Oxidation and crystallization behavior of calcium europium silicon nitride thin films during rapid thermal processing

Publication date: 31 March 2016
Source:Thin Solid Films, Volume 603
Author(s): M. de Jong, V.E. van Enter, E.W. Schuring, E. van der Kolk
Luminescent thin films were fabricated on silicon wafers using reactive magnetron sputtering of Ca, Si and Eu in Ar/N2 atmosphere. In order to activate the luminescence, the as-deposited nitride films were heated to 1100°C by a rapid thermal processing treatment. X-ray diffraction measurements reveal the crystal phases that form during thermal treatment. By recording scanning electron microscopy images of the surface and the cross-section of the film at different radial locations, the formation of different layers with a thickness depending on the radial position is revealed. Energy dispersive x-ray spectroscopy analysis of these cross-sections reveals the formation of an oxide top layer and a nitride bottom layer. The thickness of the top layer increases as a function of radial position on the substrate and the thickness of the bottom layer decreases accordingly. The observation of different 4f ⁶5d ¹ →4f ⁷ Eu²⁺ luminescence emission bands at different radial positions correspond to divalent Eu doped Ca3Si2O4N2, Ca2SiO4 and CaSiO3, which is in agreement with the phases identified by X-ray diffraction analysis. A mechanism for the observed oxidation process of the nitride films is proposed that consists of a stepwise oxidation from the as-deposited amorphous nitride state to crystalline Ca3Si2O4N2, to Ca2SiO4 and finally CaSiO3. The oxidation rate and final state of oxidation show a strong temperature–time dependency during anneal treatment.