A Study on CVD TaN as a Diffusion Barrier for Cu Interconnects
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A Study on CVD TaN as a Diffusion Barrier for Cu Interconnects Se-Joon Im*, Soo-Hyun Kim*, Ki-Chul Park**, Sung-Lae Cho*, and Ki-Bum Kim* *School of Materials Science and Engineering, Seoul National University, San 56-1, Shillimdong, Kwanak-gu, Seoul, 151-742, Korea **Samsung Electronics Co. Ltd. Kihung, Korea ABSTRACT Tantalum nitride (TaN) films were deposited using pentakis-diethylamido-tantalum [PDEAT, Ta(N(C2H5)2)5] as a precursor. During film growth, N- and Ar-ion beams with an energy of 120 eV were supplied in order to improve the film quality. In case of thermallydecomposed films, the deposition rate is controlled by the surface reaction up to about 350 °C with an activation energy of about 1.07 eV. The activation energy of the surface reaction controlled regime is decreased to 0.26 eV when the Ar-beam is applied. However, in case of Nbeam bombarded films, the deposition is controlled by the precursor diffusion in gas phase at the whole temperature range. By using Ar-beam, the resistivity of the film is drastically reduced from approximately 10000 µΩ-cm to 600 µΩ-cm and the density of the film is increased from 5.85 g/cm3 to 8.26 g/cm3, as compared with thermally-decomposed film. The use of N-beam also considerably lowers the resistivity of films (~ 800 µΩ-cm) and increases the density of the films (7.5 g/cm3). Finally, the diffusion barrier properties of 50-nm-thick TaN films for Cu were investigated aftre annealing by X-ray diffraction analysis. The films deposited using N- and Arbeam showed the Cu3Si formation after annealing at 650 °C for 1 hour, while thermallydecomposed films showed Cu3Si peaks firstly after annealing at 600 °C. It is considered that the improvements of the diffusion barrier performance of the films deposited using N- and Ar-ion beam are the consequence of the film densification resulting from the ion bombardment during film growth. INTRODUCTION The development of suitable CVD diffusion barrier in manufacturing the Cu-based metallization is critical issue because of increase of aspect ratio and fast migration of Cu into Si or SiO2. From the previous investigation, it was proved that Ta and its nitride such as Ta2N and TaN showed excellent diffusion barrier properties against Cu [1]. Among them, TaN showed the superior barrier properties. For this reason, chemical vapor deposition of TaN films has drawn much attention [2-7]. Two approaches are currently being used for the production of CVD-TaN films. The first approach is based on the reaction of TaCl5 with NH3 or N2 and H2[2]. However, high deposition temperature (>900 °C) is required. And, in case of using NH3 as a reaction gas, Ta3N5, which is dielectric, can be deposited. Other researchers used the TaBr5[3] as a source gas of tantalum in order to lower the deposition temperature. There have been several attempts to develop a CVD-TaN process by using metallorganic source gases, such as (NEt2)3Ta=Nbut (tertbutylimido-tris-diethylamido-tantalum, TBTDET) [4], Ta(NEt2)5 (pentakis-diethylamidotantalum, PDEAT) [5-6], and Ta(NMe2)5 (pentaki
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