Thermomechanical Analysis on the Phase Stability of Nitrogen-Doped Amorphous Ge2Sb2Te5 Films

The phase stability of amorphous Ge 2 Sb 2 Te 5 (GST) films affects the performance and reliability of phase change memory (PRAM) devices. The viscosity and the glass forming ability of nitrogen (N)-doped amorphous GST films were investigated in terms of thermomechanical behavior using wafer curvature measurements. The viscosity which increased by two orders of magnitude was observed in the N-doped amorphous GST film by measuring the stress relaxation accompanied by bimolecular structural relaxation. The glass forming ability ($\Delta T_{\text{x}}$), difference between the glass transition temperature ($T_{\text{g}}$) and the crystallization temperature ($T_{\text{c}}$), of GST increased as the nitrogen contents increased. These increases in the viscosity and $\Delta T_{\text{x}}$ indicate the retardation of atomic diffusion in amorphous GST and the stabilization of the amorphous phase.