Exploratory ALD Surface Chemistry
Many binary materials can be deposited using ALD techniques. However, many other materials remain to be demonstrated and other existing ALD methods could be improved using different precursors or new chemical approaches. We have been active in developing new ALD methods for various binary materials and metals. These studies are performed using FTIR and QCM techniques.
Recent materials that have been explored include MnO and MgO ALD using metal cyclopentadienyl precursors and H2O [1,2]. SiO2 ALD has been demonstrated using HSi(N(CH3)3) and H2O2 [3]. The so-called "rapid" SiO2 ALD process was also examined to understand the mechanism of this interesting reaction [4]. In addition, we have successfully grown high quality TaN ALD films using TBTDET and hydrazine [5]. Al2O3 ALD has also been grown using TMA and ozone [6].
We are currently exploring TiO2 ALD using "waterless" surface chemistry based on TiCl4 and Ti(OCH(CH3)2)4 reactants. This "waterless" surface chemistry is needed to prevent oxidation of oxygen-sensitive surfaces such as cobalt-containing films used for magnetic disks. We have determined that the isopropyl group is susceptible to beta-hydride elimination at higher ALD growth temperatures.
We are also developing Mo ALD using MoF6 and Si2H6 as the reactants. This chemical approach is analogous to W ALD using WF6 and Si2H6 as the reactants. QCM results for Mo ALD are shown in the accompanying figure. We also hope to grow W/Mo alloys to obtain more thermally stable metallic coatings that should be less likely to crystallize or restructure at higher temperatures.
1. B.B. Burton, F.H. Fabreguette and S.M. George, "Atomic Layer Deposition of MnO Using Bis(ethylcyclopentadienyl)manganese and H2O", Thin Solid Films (In Press).
2. B.B. Burton, D.N. Goldstein and S.M. George, "Atomic Layer Deposition of MgO Using Bis(ethylcyclopentadienyl)magnesium and H2O", J. Phys. Chem. C 113, 1939 (2009).
3. B. B. Burton, S. W. Kang, S.W. Rhee and S.M. George, "SiO2 Atomic Layer Deposition Using Tris(dimethylamino)silane and Hydrogen Peroxide Studied by in situ Transmission FTIR Spectroscopy", J. Phys. Chem. C 113, 8249 (2009).
4. B.B. Burton, M.P. Boleslawski, A.T. Desombre and S.M. George, "Rapid SiO2 Atomic Layer Deposition Using Tris(tert-pentoxy)silanol", Chem. Mater. 20, 7031 (2008).
5. B.B. Burton, A.R. Lavoie and S.M. George, "Tantalum Nitride Atomic Layer Deposition Using Tris(diethylamido)(tert-butylimido)tantalum and Hydrazine", J. Electrochem. Soc. 155, D508 (2008).
6. D.N. Goldstein, J.A. McCormick and S.M. George, "Al2O3 Atomic Layer Deposition using Trimethylaluminum and Ozone Studied by in situ Transmission FTIR Spectroscopy and Quadrupole Mass Spectrometry", J. Phys. Chem. C 112, 19530 (2008).
