Effect of nitrogen implantation with low dose on thermomechanical properties and microstructure of Ge2Sb2Te5 films

Abstract

Ge2Sb2Te5 (GST) films with a thickness of 300 nm, in which the nitrogen (N) implant dose was 0, 10(13), or 10(15) ionS/cm(2), were prepared by RF magnetron sputtering on Si and glass substrates. The thermomechanical properties of the GST films, viz., the biaxial modulus and coefficient of thermal expansion (CTE), were determined using the substrate curvature method for the two different substrates. The biaxial modulus of the GST films decreased with increasing N dose, whereas the CTE varied only slightly. The dependence of the microstructure on the N implantation dose was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy (FE-SEM). The lattice parameter of the crystalline structure increased with increasing N dose, which indicated the distortion of the lattice by the implanted N atoms. Because the crystallite size increased with increasing N dose, grain growth refinement caused by the formation of nitrides did not occur. Also, the presence of nitrides in the N-implanted GST film was not observed in the binding energy spectra of Is for the N element.