Influence of O(3P)/O2 Flux on the Atomic Layer Deposition of B2O3 Using Trimethyl Borate at Room Temperature

Oxygen plasma is crucial to many atomic layer deposition (ALD) processes, and O(3P) radicals play a significant role in terms of reactivity and surface modification. In situ X-ray photoelectron spectroscopy (XPS), residual gas analysis mass spectrometry (RGA-MS), and ab initio molecular dynamics (AIMD) simulations were used to study the free-radical-assisted ALD of boron oxide (B2O3) films on Si(100) using trimethyl borate [B(OCH3)3] and mixed O(3P)/O2 effluents at room temperature at varying levels of O(3P)/O2 flux to the surface. Under these conditions, no reaction with pure O2 was observed. The XPS results show that at low O(3P)/O2 flux, a complete removal of alkyl ligands is observed and C-free B2O3 is achieved, with CO2 and H2O as the main reaction products. At higher O(3P)/O2 fluxes, the formation of a stable oxidized C surface layer is observed with some C incorporation into the growing B2O3 film. In both flux regimes, the B2O3 film thickness increased linearly with the number of cycles, consistent with an ALD process. AIMD simulations of O(3P) collisions with B(OCH3)3 indicate a multistep ligand removal mechanism initiated by hydrogen abstraction at a threshold O(3P) energy of ∼0.1 eV, consistent with RGA-MS results. In contrast, C oxidation and incorporation in the high-flux regime result from O2 termination of the O(3P)-induced C radical sites. This work demonstrates that the purity of B2O3 films, efficiency of ligand removal, and surface reaction products can be flux-dependent.