Emslie Group Research: ALD

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Research area 1: ALD

Research Area 2: Ln/An

Research Area 3: M---B

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New Organometallic Reactivity for Metal Atomic Layer Deposition (ALD)

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Atomic layer deposition is a technique for the deposition of highly conformal, uniform thickness, ultrathin films with applications in microprocessors, dynamic random access memory, electroluminescent displays, solar cells, fuel cells, photonic devices and catalysis. For many applications, thin metal, metal oxide, metal nitride etc. films were traditionally deposited using Chemical Vapour Deposition (CVD). In CVD, vapors of a volatile metal complex are passed over the surface of a substrate which is heated above the decomposition temperature of the metal complex. However, CVD has various limitations, including the formation non-uniform films. This is particularly problematic if only a very think film is desired or if the substrate has high aspect ratio features such as deep trenches in the surface. To resolve these problems, the process of Atomic Layer Deposition (ALD) was developed. ALD is related to the process of CVD, in that the metal source is a volatile metal complex. However, deposition is achieved not by thermal decomposition of a metal complex on a heated substrate surface (CVD), but by repeated alternating surface controlled reactions between a volatile metal precursor and a volatile co-reactant, at least one of which is physically or chemically adsorbed on the substrate surface prior to reaction. The byproducts of these surface reactions must be sufficiently volatile and thermally stable to allow their removal in the purge steps which separate each metal precursor and co-reagent pulse. In this way completely uniform and conformal metal films can be deposited. Metal oxide films are typically deposited using water, oxygen or ozone as the co-reagent, metal nitride films are typically deposited using ammonia, and metal sulfide films typically employ hydrogen sulphide as the co-reagent. Metal films are more difficult to deposit; metal ALD has only been achieved for W, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt and Cu, typically using oxygen (for noble metals only) or hydrogen as the co-reagent. However, most existing methods for metal ALD operate at high temperature (>200 °C) or employ non-selectively reducing or oxidizing co-reagents which limits their utility. The Emslie group ALD reasearch program is focused on the development and study of new organometallic reactivity for metal ALD. Our initial publications in the field focused on copper metal, but a range of metals are under investigation. Regardless of the target metal, our research involves precursor and co-reagent design and synthesis, solution deposition reactions and thin film characterization, solution reactivity/mechanistic studies, and ALD studies (via collaboration). All of this research relies on our expertise in air-sensitive coordination and organometallic chemistry. Overcoming the current limitations in ALD is a particularly important goal since over the next 5-10 years, rapidly decreasing device dimensions are expected to render ALD the only suitable process for the preparation of a wide variety of technologically important materials in the form of thin (from an atomic layer to several nanometres), uniform and continuous films, especially on surfaces with high aspect-ratio features such as narrow, steep-sided trenches. Much of this work is carried out in collaboration with Intel Corporation.

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