Tantalum diffusion barrier grown by inorganic plasma-promoted chemical vapor deposition: Performance in copper metalliza
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Barry Arkles Gelest Inc., Tullytown, Pennsylvania 19007 (Received 1 February 1999; accepted 13 September 2000)
As-deposited and annealed tantalum films, grown by plasma-promoted chemical vapor deposition (PPCVD) using pentabromotantalum and hydrogen as coreactants, were evaluated as diffusion barriers in copper metallization. Stacks consisting of 500-nm-thick sputtered Cu/55-nm-thick untreated PPCVD Ta/Si were annealed in argon in the range 450 to 650 °C, in 50 °C intervals, along with sputtered Cu/preannealed PPCVD Ta/Si and sputtered Cu/sputtered Ta/Si stacks of identical thickness. Pre- and postannealed stacks were characterized by x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, hydrogen profiling, x-ray diffraction, atomic force microscopy, sheet resistance measurements, and Secco chemical treatment and etch-pit observation by scanning electron microscopy. The sputtered and preannealed PPCVD Ta films acted as viable diffusion barriers up to 550 °C, while the as-deposited PPCVD Ta films failed above 500 °C. In all cases, breakdown occurred through the migration of Cu into Si, rather than an interfacial reaction between Ta and Si, in agreement with previously reported results for sputtered Ta films. The accelerated barrier failure for as-deposited PPCVD Ta might have been caused by the presence of approximately 20 at.% hydrogen in the as-deposited PPCVD Ta, an observation which was supported by the enhanced performance of the same PPCVD Ta films after annealing-induced hydrogen removal.
I. INTRODUCTION
The successful incorporation of copper-based metallization schemes in emerging ultra-large-scale-integration (ULSI) computer chip device generations requires the identification and development of viable diffusion barrier/adhesion promoter material technologies.1 These “liner” materials are required to prevent undesirable diffusion and interaction between copper and the semiconductor and dielectric regions of the chip. In particular, it is well known that the presence of copper in silicon leads to the formation of deep trap levels that cause serious device degradation and failure. As device size continues its trend toward smaller features, the liners must provide enhanced barrier performance at reduced thickness in order to maximize space availability for the actual conductor.
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J. Mater. Res., Vol. 15, No. 12, Dec 2000 Downloaded: 26 Mar 2015
Various refractory material systems, primarily transition metals and their binary and ternary nitrides, have been extensively investigated for liner applications in copper metallization.2 In this respect, tantalum-based material systems are perhaps the most studied because of their highly desirable physical, chemical, mechanical, and electrical properties.3 These advantageous properties are further enhanced by the thermodynamic stability of Ta and its nitrides with respect to Cu, given the absence of Cu–Ta or Cu–N compounds. Experimenta
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