Optimum Growth Conditions of Ge–Sb–Te Alloy Thin Film Investigated by Ellipsometry

Abstract

The ellipsometric constants ψ and Δ of phase changing Ge₂Sb₂Te₅ (GST) used as an optical recording medium were collected during film growth, and the optimum growth conditions of GST thin film were investigated by varying variables such as Ar gas pressure, DC power and substrate temperature. The density distribution of postgrowth GST thin films was determined by ex situ spectroellipsometry. Based on density distribution information of the postgrown GST thin films, the evolution of density distribution of GST thin films during growth was monitored using an in situ ellipsometer. Based on ellipsometric analysis, we found that the optimum growth conditions for attaining the most homogeneous density distribution are Ar gas pressure of 7 mTorr, DC power of 45 W, and substrate temperature of 150°C. These optimum growth conditions were independently verified from scanning electron microscopy (SEM) images.