Low temperature deposition of Ba_1-xSr_xTiO₃ thin films by ECR plasma-enhanced metalorganic chemical vapor deposition

Abstract

The deposition temperature dependence of Ba_0.7Sr_0.3TiO₃ (BST) thin film physical and electrical properties was investigated. Films were deposited between 250 and 500°C by electron cyclotron resonance (ECR) plasmaenhanced liquid source metalorganic chemical vapor deposition (MOCVD). Depositions were carried out in an oxygen plasma using the precursors Ba(thd)₂•(polyamine), Sr(thd)₂•(polyamine), and Ti(O-i-Pr)₂(thd)₂. With a constant ECR plasma power, composition and growth rate were independent of temperature within the full range investigated, in contrast to most thermally-driven CVD BST processes. Films grown above 350°C were crystalline as-deposited on Pt, and were (100)-textured. The dielectric properties depended strongly upon BST crystallinity, with a sharp increase in dielectric constant and its field dependence observed above 350°C. For slightly Ti-rich, 800Å thick films, dielectric constants of 281 were obtained at 500°C, following a 550°C top electrode anneal in O₂. Over the full deposition temperature range investigated, the leakage current density was less than 10^-7 A/cm² at 2.0 V and dielectric loss tangents varied between 0.003 and 0.013.

Key Words:

• BST
• thin films
• MOCVD
• ECR plasma
• low temperature