| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoM |
| Session: | ALD Precursors and Surface Reactions |
| Presenter: | Charith Nanayakkara, The University of Texas at Dallas |
| Authors: | C.E. Nanayakkara, The University of Texas at Dallas A. Vega, The University of Texas at Dallas G. Liu, SAFC Hitech C. Dezelah, SAFC Hitech R. Kanjolia, SAFC Hitech Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) is an attractive technique for thin film deposition due to its sequential and self-limiting surface reactions leading to conformal and controlled film growth. However, nucleation delays (incubation) can lead to non-uniform island growth, particularly for metal films, often requiring many cycles to obtain a continuous film.
Molybdenum oxide thin films are important for a number of electrical, catalytic, and optical applications. Several Mo precursor-oxidant combinations have been used. For instance, molybdenum hexacarbonyl and ozone (with ALD window between 152 and 172 0C),1 and Bis(tert-butylimido)bis(dimethylamido) molybdenum and ozone (with an ALD window between 250 and 300 0C)2 gave good film with higher nitrogen content at deposition temperatures less than 250 0C for the latter.2 The use of oxygen plasma with bis(tert-butylimido)bis(dimethylamido) molybdenum has shown film growth between 50 - 350 0C with high elemental H (4 – 11%).3
Here, we introduce a new molybdenum precursor, Si(CH3)3CpMo(CO)2(η3-2-methylallyl)) (MOTSMA), which has a good thermal stability (>200 °C ), higher volatility with increased vapor pressure (3s exposure results 0.6 Torr gas phase pressure with bubbler at 90 0C), and increased deposition rates. However, In-situ FTIR spectroscopy of the MOTSMA and ozone ALD process reveals that there is a ~15 cycle incubation period at 250°C on OH-terminated oxidized Si(100) surfaces. After this incubation period, i.e. once the steady state ALD process is established, the expected ligand exchange is observed, with formation of surface Si(CH3)3CpMo(η3-2-methylallyl) species after the precursor exposure and their removal during the ozone pulse, resulting in Mo(=O)2 surface species. Since this nucleation delay can be reduced by raising the temperature above 300°C, the initial adsorption of the precursor on OH-terminated surfaces was examined as a function of temperature. Indeed, this initial adsorption of MOTSMA on OH-terminated surfaces was found to require higher temperatures. Therefore, we used an initial 350 0C MOTSMA grafting step in order to overcome the nucleation delay but then performed the ALD process at 250 0C and 300 0C. In this manner, steady state film growths with no nucleation delay were obtained at both temperatures, with stoichiometric composition (MoO3) as confirmed by X-ray photoelectron spectroscopy. The current study highlights the critical role of precursor grafting on eliminating the nucleation delay for ultra-thin ALD grown film deposition.
1. J. Mat. Chem. 2011, 21, 705
2. J. Vac. Sci. & Tech. A 2014, 32, 01A119
3. J. Vac. Sci. & Tech. A 2016, 34, 01A103