Synthesis of Dielectric Al-Doped HfO2 Thin Film by Polymer-Assisted Deposition

Abstract

As transistors scale down, demands for high-k dielectric materials increase. Among various dielectric materials, HfO2 have drawn attention because of its large band gap, high dielectric constant, and excellent physical/chemical stability. Although several solution-based synthesis have been developed, their dielectric properties are inferior to those obtained by conventional vacuum processes (e.g., atomic layer deposition, sputtering). This study demonstrates a solution-based polymer-assisted deposition (PAD) of high-k Al-doped HfO2 thin films exhibiting excellent dielectric properties comparable to the conventional deposition methods. The PAD process enables the control of film thickness (≥3 nm) and the homogenous Al doping in the entire thin film. The key to the success is HCl-mediated coordination of metal ions and polymer. Systematic analysis on the structure and chemical composition of the dielectric layer is carried out. It is found that the phase transition from monoclinic phase to a mixture of tetragonal and amorphous phases results in excellent dielectric properties. The 7.8 nm thick thin film doped with 4.1 at% of Al exhibits a high dielectric constant of 30.2 with a high areal capacitance (674 nF cm−2 at 1.0 kHz), a low leakage current (3.3 × 10−9 A cm−2 at 2.0 MV cm−1), and a high breakdown voltage (7.7 V).