Published: May 19, 2011 r2011 American Chemical Society 11507 dx.doi.org/10.1021/jp1059374 | J. Phys. Chem. C 2011, 115, 11507–11513 ARTICLE pubs.acs.org/JPCC Atomic Layer Deposition of Tantalum Nitride Using A Novel Precursor Shikha Somani, † Atashi Mukhopadhyay, † and Charles Musgrave* ,‡ † Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States ‡ Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States ’ INTRODUCTION As the components of microelectronics shrink to increasingly smaller dimensions, new materials and processes to produce these structures are required. An area that has been of particular interest is the fabrication of metal interconnects that link the separate devices in integrated circuits and the materials that are used to make them. Copper has become the material of choice for interconnects due to its good mechanical properties and low resistivity compared to the previously dominant interconnect material, aluminum. However, Cu exhibits a high diffusivity, making it prone to diffusion into neighboring structures. As a result, much research has focused on exploring new materials to be used as Cu diffusion barriers. In particular, transition metal nitrides such as tantalum nitride, tungsten nitride, and titanium nitride, have all been identified as good candidates for copper diffusion barriers in microelectronics. 1À3 Tantalum nitrides are particularly promising because they are stable up to extremely high temperatures and are unreactive toward Cu. 4 Scaling of interconnects to current line widths has led to severe requirements for barrier materials. For instance, because barrier materials are poor electrical conductors, their thicknesses must be kept to a minimum in order to maintain copper interconnect’s resistance advantage over Al. Furthermore, in cases where via and trench liner materials are deposited between metal layers, for example at the bottom of a via connected to a lower metal level, the barrier material should be thin to reduce electrical resistance by allowing electron tunneling across the barrier interlayer. While ultrathin thicknesses are desired, barrier films must be deposited so as to avoid pinholes that could lead to shorting of the interconnect. One method capable of depositing ultrathin, con- formal and pinhole-free films is atomic layer deposition (ALD). ALD (sometimes called atomic layer epitaxy) has been shown to be an effective method of depositing TaN and has been shown to have several advantages over competing techniques, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). 5À10 PVD is a vacuum deposition process that involves creating vapor phase species, usually either by evaporation or sputtering, that deposit on a substrate by condensation, rather than chemical reaction. Although PVD is effective in depositing films at reasonably low temperatures, it is a line of sight process and can have difficulty in achieving satisfactory uniformity, film thickness and film quality for the demanding industry require- ments for next-generation microelectronics. CVD involves vaporizing precursors that deposit on a substrate by chemically reacting with it. Although CVD is better able to fulfill the strict constraints on the film than PVD, it does not achieve the same uniformity, conformality, ultrathin thicknesses, and absence of pinholes as ALD because unlike ALD, the surface reactions are not self-limiting. Consequently, ALD has proven a viable alternative when atomic layer thicknesses and thickness control of pinhole- free films are desired. Received: June 28, 2010 Revised: March 23, 2011 ABSTRACT: We use B3LYP hybrid density functional theory to investigate atomistic mechanisms for the atomic layer deposition (ALD) of tantalum nitride (TaN) grown using tert -butylimidotris(diethylamido)tantalum [( t BuN)- (NEt 2 ) 3 Ta, TBTDET], and ammonia (NH 3 ) as precursors. Our calculations examine various possible mechanisms for TaN growth by ALD and metal organic chemical vapor deposition (MOCVD). In particular, we identify low barrier (10.6 and 27.6 kcal/mol) ligand exchange mechanisms with NH 3 that lead to incorporation of NH 3 ’s nitrogen into the film. Ligand exchange with NH 3 is thermodynamically and kinetically favored over competing mechanisms that incorporate nitrogen from the metal precursor including: β-hydrogen elimina- tion of isobutene or ethene; and NH 3 catalyzed β-hydrogen elimination of isobutene or ethene. β-hydrogen elimination of isobutene or ethene is found to proceed through a barrier of 76.0 kcal/mol. However, our results indicate that ammonia or diethylamine produced by precursor reaction with surface amine groups can also catalyze β-hydrogen elimination of isobutene with a predicted barrier of 64.3 kcal/mol, thus making MOCVD reactions kinetically active above ∼600 °C. In addition to providing a fundamental understanding of the chemistry of TaN ALD from ( t BuN)(NEt 2 ) 3 Ta and NH 3 , the set of mechanisms analyzed provide new insights into the principles governing the ALD processes of other metal nitride films using imido or amido ligand transition metal complexes and ammonia as precursors.