In-Situ XPS Study on ALD (Atomic Layer Deposition) of High-k Dielectrics: La_2O_3 using La-formidinate and Ozone

摘要

The detailed growth behavior of lanthanum oxide (La_2O_3) on a silicon substrate during atomic layer deposition (ALD) is investigated by in-situ, x-ray photoelectron spectroscopy (XPS) following individual ALD pulses of tris(N,N'-diisopropyl-formamidinato) lanthanum [La('PrfAMD)3] and highly concentrated ozone (～390 g/m~3). At the initial growth stage, ozone oxidized the La-ligand as well as the silicon substrate. During oxidation of silicon substrate, a noticeable amount of silicon atoms diffused into growing La_2O_3 film, resulting in Si-rich and La-rich La-silicates showing composition gradient of La/Si at the deposition temperature of 250 ℃. The amount of La-silicate after third ALD cycle reached more than 50 % of that generated by 30 cycles. As the thickness of the film increased with sequential ALD cycles, the substrate oxidation as well as the out-diffusion of Si atoms becomes a negligible quantity, and the pure La_2O_3 film starts growing leaving La-silicate layers at the interface.