A Study on Properties of HfO2 Thin Film via Plasma Enhanced Atomic Layer Deposition Using a Noble Heteroleptic Hafnium Precursor

Abstract

With the recent advanced technology, the performance of display devices in electronic products have been improved and high power consumption is required. To solve the problem of power consumption, the introduction of high-k materials to a display device as a gate dielectric is considered, which is already used being used in complementary metal–oxide–semiconductor (CMOS) devices. Among high-k materials, HfO2 is a promising candidate for gate dielectric in thin film transistors (TFTs) which has excellent properties with a high k value (~25), a wide bandgap (~5.7 eV), thermal stability, and chemical stability on Si. The characteristics of HfO2 film are changed according to the method to deposit the thin film. Various techniques for depositing of HfO2 films have been reported, and ALD is of great interest in field of advanced microelectronics because of its ability to precisely control film thickness at the atomic scale, excellent step coverage, and low process temperature. In this study, plasma-enhanced atomic layer deposition (PEALD) of HfO2 films were conducted using a novel (η5:η1- Cp(CH2)2NMe)Hf(NEtMe)2 (MAP-Hf01) precursor and Ar/O2 plasma as a co-reactant. The self-limiting growth behavior of atomic layer deposition with nearly constant growth per cycle at 0.65 Å/cycle was observed and the O/Hf ratio was similar to that of bulk HfO2, irrespective of deposition temperature from 200℃ to 400℃. With increasing HfO2 deposition temperature, the crystallinity and density of the HfO2 film also increased, however, the concentration of the OH-related defects and surface roughness showed the opposite tendency. Notably, the HfO2 film deposited at 400℃ exhibited the lowest level of hafnium suboxide (HfOx) and the highest crystallinity in monoclinic phase. The electrical properties of HfO2 with varying deposition temperature were determined by current density-electric field (J-E) and capacitance-applied voltage (C-V) measurements. Consequently, 200℃ HfO2 TFT showed high electrical performance (saturation mobility of 37.72 cm2/Vs, sub-threshold swing of 0.11 V/decade, and on/off current ratio of 8.34ⅹ108), resulting that MAP-Hf01 is an appropriate Hf precursor for the deposition of HfO2 in advanced display devices.