| AVS 60th International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+EM+NS+SS-ThA |
| Session: | Thin Film: Growth and Characterization II |
| Presenter: | J.R. Abelson, University of Illinois at Urbana Champaign |
| Authors: | A.N. Cloud, University of Illinois at Urbana Champaign J.L. Mallek, University of Illinois at Urbana Champaign K.A. Arpin, University of Illinois at Urbana Champaign P.V. Braun, University of Illinois at Urbana Champaign G.S. Girolami, University of Illinois at Urbana Champaign J.R. Abelson, University of Illinois at Urbana Champaign |
| Correspondent: | Click to Email |
Chemical vapor deposition can afford smooth and conformal films in high aspect ratio structures in the limit of high precursor pressure and low substrate temperature. Under those conditions, adsorbed precursor molecules cover the growth surface, react to deposit film at useful rates, but also block active sites such that the effective sticking coefficient is reduced. The result – a conformal film in trenches deeper than 30:1 – can be competitive with ALD. This is not surprising, given the underlying kinetic principle, surface site-blocking, is the same.
We report the successful implementation of the most extreme parameters: we perform static CVD in an unpumped glass tube that is pre-filled with precursor up to its vapor pressure and slowly ramped to temperature in a clamshell furnace. The slow heating ramp at maximum possible precursor pressure affords remarkably uniform film nucleation, excellent conformality and surface smoothness. Based on the coating of deep trenches, silica-based synthetic opals, and aerogels, we estimate an effective sticking coefficient < 10-5. Many substrates can be loaded into the tube such that the throughput is good in batch mode. The precursor utilization is excellent (~ 25 %), unlike the case of flowing CVD in which most of the precursor is wasted under conformal growth conditions.
Static CVD is demonstrated for the conformal growth of HfB2 and elemental Fe films. HfB2 is an electrically conductive refractory material with high mechanical hardness, excellent tribological properties, and excellent diffusion barrier properties against Cu. The precursor, Hf(BH4)4, has a remarkably high vapor pressure of 15 Torr at 25°C. This pressure both promotes conformal film growth and provides a large gas density sufficient to deposit 100 nm of film in a single cycle. The precursor is reactive toward O2 and H2O and acts as a gas-phase getter for potential contaminants. Thus, despite the rough vacuum apparatus, the films have O and C impurity contents < 1 at. % as evaluated by AES. The film composition is stoichiometric despite the buildup of reaction products. This implies that the growth surface has no net reactivity towards these products.
Fe films are deposited from the precursor Fe(CO)5. Typically CVD Fe films grown from this precursor have faceted surfaces and are not conformal. Here, the film smoothness and conformality is excellent. The O and C impurity contents are ~ 1 at. %.
We will discuss the prospects for coating other materials by static CVD, as well as simple modifications that have the potential to afford thicker films and avoid impurity contamination in cases where the byproduct reactions are not negligible.