The Enhanced Dielectric and Insulating Properties of Al₂O₃ Modified Ta₂O₅ Thin Films

Abstract

Future-generation memory devices will require materials with higher dielectric constants compared to conventional dielectric materials such as silicon oxide and silicon nitride. Tantalum oxide (Ta₂O₅) is one of the most promising high dielectric constant materials because of its ease of integration into conventional VLSI processes compared to other complex oxide dielectrics. The dielectric constant and thermal stability characteristics of bulk Ta₂O₅ samples were previously reported to enhance significantly through small substitutions of Al₂O₃. However, this improvement in the dielectric constant of (1 − x)Ta₂O₅-xAl₂O₃ was not clearly understood. The present research attempts to explain the higher dielectric constant of (1 − x)Ta₂O₅-xAl₂O₃ by fabricating thin films with enhanced dielectric properties. A higher dielectric constant of 42.8 was obtained for 0.9Ta₂O₅-0.1Al₂O₃ thin films compared to that reported for pure Ta₂O₅ (25–30). This increase was shown to be closely related to a-axis orientation. Pure Ta₂O₅ thin films with similar a-axis orientation also exhibited a high dielectric constant of 51.7, thus confirming the orientation effect. Systematic study of dielectric and insulating properties of (1 − x)Ta₂O₅-xAl₂O₃ thin films indicate improved leakage current properties and reliability characteristics such as temperature coefficient of capacitance and bias stability with increase in Al₂O₃ concentrations.