The Growth of Tantalum Thin Films by Plasma-Enhanced Atomic Layer Deposition and Diffusion Barrier Properties
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The Growth of Tantalum Thin Films by Plasma-Enhanced Atomic Layer Deposition and Diffusion Barrier Properties H. Kim, C. Cabral, Jr., C. Lavoie, and S.M. Rossnagel IBM Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598 ABSTRACT Ta films were grown by plasma-enhanced atomic layer deposition (PE-ALD) at temperatures from room temperature up to 300 °C using TaCl5 as source gas and RF plasma-produced atomic H as the reducing agent. Post-deposition ex situ chemical analyses showed that the main impurity is oxygen, incorporated during the air exposure prior to analysis with typically low Cl concentration below 1 at %. The X-ray diffraction indicates that ALD Ta films are amorphous or composed of nano-grains. The typical resistivity of ALD Ta films was 150-180 µΩ cm, which corresponds to that of β-Ta phase, at a wide range of growth parameters. The conformality of the film is 100 % up to an aspect ratio of 15:1 and 40 % for aspect ratio of 40:1. The thickness per cycle, corresponding to the growth rate, was measured by Rutherford back scattering as a function of various key growth parameters, including TaCl5 and H exposure time and growth temperature. The maximum thickness per cycle values were below 0.1 ML, probably due to the steric hindrance for TaCl5 adsorption. Bilayer structures consisting of Cu films deposited by sputtering and ALD Ta films with various thicknesses were prepared and the diffusion barrier properties of ALD Ta films were investigated by various analysis techniques consisting of X-ray diffraction, elastic light scattering, and resistance analysis. The results were compared with Ta thin films deposited by sputtering with comparable thicknesses. Also, the growth of TaN films by PE-ALD using consecutive exposures of atomic H and activated N2 is presented. INTRODUCTION As device dimensions shrink, Cu interconnects become the best choice due to higher electromigration resistance, and thus reliability, as well as higher conductivity compared to Al wiring.(1,2,3) However, Cu has higher diffusivity and easily diffuses through dielectrics, producing deep level defects in Si which are detrimental to the performance of CMOS transistors.(3-4) Thus, a thin, stable diffusion barrier with high conformality is an essential requirement for Cu interconnect technology. The requirements of these diffusion barriers include high thermal stability, low resistivity, and low reactivity with Cu. Recently, atomic layer deposition (ALD) has been studied intensively due to its inherently high conformality. This is because the ALD process is intrinsically self-limited. The metal-containing precursor, often either a halide or metal-organic source, is introduced and completely removed from the sample chamber, aside from the adsorbed monolayer, prior to the introduction of the second species which initiates the chemical reaction. Then, the second species, plus the product molecules, are completely removed from the chamber prior to exposure to another pulse of the metal-containing precursor. We have recently stu
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