Reactive Force Field Molecular Dynamics Studies of the Initial Growth of Boron Nitride Using BCl₃ and NH₃ by Atomic Layer Deposition

A new ReaxFF reactive force field for the atomic layer deposition (ALD) of boron nitride (BN) thin film growth using BCl₃ and NH₃ has been developed, and the initial stage of the BN growth is numerically demonstrated by ReaxFF reactive force field-based molecular dynamics (ReaxFF MD). Based on density functional theory, the ReaxFF parameters were carefully trained to describe BCl₃ geometries and simulate surface reactions with BCl₃ and NH₃, forming BN films and HCl. The ALD process was simulated by repeating four steps: (1) BCl₃ pulse, (2) first purge, (3) NH₃ pulse, and (4) second purge. The film growth simulation indicates that BN thin films are grown through five steps: (i) BCl₃/NH₃ surface diffusion, (ii) BN cluster formation/growth, (iii) HCl formation, (iv) HCl surface diffusion, and (v) HCl desorption. Through the 5 cycles of ALD simulation, we found a mixed growth mechanism of three-dimensional growth in the form of clusters and two-dimensional growth in the form of thin films. The substrate temperature strongly affects the initial growth behavior and the resulting thickness of the BN thin film. A moderate temperature favors the formation and growth of BN clusters, while too high temperature hinders the growth of thin films because of the desorption of gas molecules and BN clusters on the surface. Through our simulation, we show that the ReaxFF MD is capable of approaching nanoscale surface reactions and clarifying the mechanisms of ALD with an atomic scale, which should be a powerful method to realize a wafer-scale ALD simulation by combining with macroscale methods.