Atomic layer deposition of aluminum fluoride using Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e and SF\u3csub\u3e6\u3c/sub\u3e plasma

\u3cp\u3eMetal fluorides typically have a low refractive index and a very high transparency and find many applications in optical and optoelectronic devices. Nearly stoichiometric, high-purity AlF\u3csub\u3e3\u3c/sub\u3e films were deposited by atomic layer deposition (ALD) using trimethylaluminum [Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e] and SF\u3csub\u3e6\u3c/sub\u3e plasma. Self-limiting growth was confirmed and the growth per cycle was determined to range from 1.50 Å to 0.55 Å for deposition temperatures between 50 °C and 300 °C. In addition, the film density of ∼2.8 g cm\u3csup\u3e-3\u3c/sup\u3e was found to be relatively close to the bulk value of 3.1 g cm\u3csup\u3e-3\u3c/sup\u3e. Vacuum ultraviolet spectroscopic ellipsometry measurements over the wavelength range of 140-2275 nm showed a refractive index n of 1.35 at 633 nm, and an extinction coefficient k of <10\u3csup\u3e-4\u3c/sup\u3e above 300 nm, for all deposition temperatures. Optical emission spectroscopy during the SF\u3csub\u3e6\u3c/sub\u3e plasma exposure step of the ALD cycle revealed the formation of C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e and CF\u3csub\u3e2\u3c/sub\u3e species, resulting from the interaction of the plasma with the surface after Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e exposure. On the basis of these results, a reaction mechanism is proposed in which F radicals from the SF\u3csub\u3e6\u3c/sub\u3e plasma participate in the surface reactions. Overall, this work demonstrates that SF\u3csub\u3e6\u3c/sub\u3e plasma is a promising co-reactant for ALD of metal fluorides, providing an alternative to co-reactants such as metal fluorides, HF, or HF-pyridine.\u3c/p\u3