Conformal coating of boron-containing films via atomic layer deposition (ALD) could be used as a shallow dopant source for advanced 3D-transistor structures in VLSI manufacturing. Aiming this application, fluorine (F) -free precursors of boron such as boric acid (B(OH)₃) and trimethyl borate (B(OCH₃)₃) were explored as ALD precursors in a combination with Al₂O₃ ALD process. The ALD of Al₂O₃ was performed using trimethyl aluminum (Al(CH₃)₃) and Deionized H₂O. The complex chemistry resulted in deposition of boron containing composite films of (B_xAl_2-xO₃). In-situ quartz crystal microbalance study was performed to evaluate the optimum ALD precursors dose times as well as confirms the self-limiting behavior of the ALD processes. Growth rate of composite B_xAl_2-xO₃ processes under various ALD conditions are in the range of 0.8-1.1Å. The resultant boron containing B_xAl_2-xO₃ films was analyzed for composition by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), ellipsometry, and electrical capacitance measurements. Atomic composition of B was tailored by adjusting relative ratio of the B to Al precursors cycle during ALD process. A rapid thermal annealing was performed as a function of time and temperature and confirms B-diffusion in the Si(wafer) as well as changes in optical properties of the B_xAl_2-xO₃ layers. Here we will present detailed investigation of ALD grown B_xAl_2-xO₃ layers.