ALD and PEALD deposition of HfO2 and its effects on the nature of oxygen vacancies

Abstract

The high-k materials are essential in thin-film transistors. A well-controlled thin film deposition that produces less electronic defects induced by charged vacancies is highly desirable for avoiding high leakage current and and providing an exceptional dielectric strength. This work addresses the use of atomic layer deposition (ALD), plasma-enhanced ALD (PEALD), and its variants to produce low-defective HfO2. The X-ray photoelectron spectroscopy (XPS) and Capacitance-Voltage (C-V) analysis revealed that the thermal ALD (TALD) samples produce electron emissions of ∼ 1 eV above the valence band maximum, negative flat band voltage shift of 1.51 V, and low dielectric breakdown strength (4.37 MV/cm). These properties confirm the high density of positive oxygen vacancies (1.2 × 1013 cm−2) acting as shallow traps, despite its O/Hf ratio (1.84) being higher than the Direct Plasma ALD (DPALD) sample. On the other hand, PEALD induces the formation of neutral vacancies promoted by the electric field of the plasma sheath. These defects are less detrimental to the capacitor performance as their flat band shifts are −0.25 and 1.01 V for remote plasma ALD (RPALD) and DPALD samples. Their dielectric breakdown strength increases by ∼ 1 MV/cm, and a reduced current density by 3 orders of magnitude less than TALD samples. The O/Hf ratio in DPALD samples is 1.80, confirming the benefits of using PEALD approaches.