Investigation of Grain Effect in Heat Transfer for less than - 10nm Local Areas of HfO₂ Thin Film Deposited with Atomic Layer Deposition

Recently, the rapid development of the material science and nano-atomic technology has led to the development of device made up of dozens of atoms such as nanoparticles(0D), nanowires(1D), 2D atomic materials, ultra-thin film. In particular, the atomic layer deposition(ALD) method is attracted attention as a key technology that can produce ultra-thin films at the atomic level. In the ultra-thin film, because the size of a material becomes similar to or less than the size of the quantum mechanical wave of particle or the energy carrier’s collision distance (mean free path, MFP), a novel quantum mechanical characteristics occurs. Therefore, novel heat transfer mechanisms should exist in angstrom-scale materials. We can predict that a difference or a restriction in the quantum heat transfer exist based on the crystal structure and thin-film thickness obtained from previous theoretical studies. However, the heat transfer mechanism has not been proven owing to the difficulty of the experimental approach and the lack of measurement techniques in the atomic or angstrom scale. In addition, only the totally averaged thermal conductivity is reported regarding the annealing effect of the thin film, and the relationship between grain size and heat transfer by annealing is not closely analyzed. In this study, we used scanning thermal microscopy(SThM) to investigate heat transfer differences occurring in a local area less than ~10 nm in HfO₂ thin films. The difference in averaged thermal conductivity and distribution of thermal conductivity in the local area according to the thickness of the thin film was investigated. In addition, the crystal structure was changed through annealing, and the thermal conductivity of the thin film according to grain size was investigated. The thermal transfer mechanism investigated in this work according to the crystal structure will be an important background for the development of innovative device using ALD method. It is also expected that the SThM system used in this study will be actively used for future research that can provide insight of new heat transfer mechanisms in the atomic scale.