Crystallization of Atomic Layer Deposited MgO Thin Filmsas a Buffer Layer for Rocksalt Beo Film Growth

Abstract

Rocksalt structure beryllium oxide (BeO) thin film has been highlighted as an exceptional high-k dielectric material for various semiconductor device application because it can have a very high-k value of > 200 and high band gap of ~ 10 eV simultaneously. However, this was an only theoretical expectation based on the first-principles calculation. Also, the stable crystal structure of BeO is wurtzite at normal thermal Atomic Layer Deposition (ALD) processing conditions of which k-value is only ~8, whereas the rocksalt structure BeO could be stabilized only under an extremely high-pressure condition (> 100 GPa). Therefore, it is expected that the usual ALD process of BeO film may result in the wurtzite structure film. Considering the interfacial tensile strain offered by the larger MgO lattice parameter with a cubic-based rocksalt crystal structure, which is 4.21 Å while BeO lattice parameter is 2.70 Å for hexagonal-based wurtzite crystal structure and 3.62 Å for cubic-based rocksalt crystal structure, the adoption of cubic-based MgO as a buffer layer may enable the transition of BeO crystal structure from wurtzite to quasi-rocksalt. This work reported the optimization of both Thermal and Plasma-Enhanced ALD (TALD, and PEALD) process and post-annealing conditions of MgO and their influences on the crystallization properties of BeO on top of the MgO buffer layer, observed by X-Ray Diffraction (Figure 1 (a), (b)), Transmission Electron Microscope Selected Area Diffraction. Moreover, the electronic properties of MgO and BeO thin films, especially leakage current and dielectric constant, were verified through the measurement of Metal-Insulator-Metal (MIM) device (Figure 1 (c)). This work, thus, attempted to grow MgO film by TALD, and PEALD as a buffer layer for the rocksalt BeO film growth. Although the growth of the BeO film on top of the rocksalt MgO film is ongoing project, this work can provide a fundamental step toward the final goal of rocksalt BeO film growth by an ALD method. Figure 1