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Study of Ta as a Diffusion Barrier in Cu/SiO2 Structure

Published online by Cambridge University Press:  17 March 2011

J. S. Pan,
A. T. S. Wee,
C. H. A. Huan,
J. W. Chai and
J. H. Zhang
J. S. Pan
Affiliation:
Institute of Materials Research & Engineering, 3 Research Link, Singapore 117602
A. T. S. Wee
Affiliation:
Department of Physics, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
C. H. A. Huan
Affiliation:
Department of Physics, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
J. W. Chai
Affiliation:
Institute of Materials Research & Engineering, 3 Research Link, Singapore 117602
J. H. Zhang
Affiliation:
School of Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798
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Abstract

Tantalum (Ta) thin films of 35 nm thickness were investigated as diffusion barriers as well as adhesion-promoting layers between Cu and SiO2 using X-ray diffractometry (XRD), Scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). After annealing at 600°C for 1h in vacuum, no evidence of interdiffusion was observed. However, XPS depth profiling indicates that elemental Si appears at the Ta/SiO2 interface after annealing. In-situ XPS studies show that the Ta/SiO2 interface was stable until 500°C, but about 32% of the interfacial SiO2 was reduced to elemental Si at 600°C. Upon cooling to room temperature, some elemental Si recombined to form SiO2 again, leaving only 6.5% elemental Si. Comparative studies on the interface chemical states of Cu/SiO2 and Ta/SiO2 indicate that the stability of the Cu/Ta/SiO2/Si system may be ascribed to the strong bonding of Ta and SiO2, due to the reduction of SiO2 through Ta oxide formation.

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