Stress gradients observed in Cu thin films induced by capping layers
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Paul R. Besserb) Advanced Micro Devices, Sunnyvale, California 94088
Christian Witt GlobalFoundries, T.J. Watson Research Center, Yorktown Heights, New York 10598
Jean L. Jordan-Sweet IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (Received 27 August 2009; accepted 23 November 2009)
Glancing-incidence x-ray diffraction (GIXRD) has been applied to the investigation of depth-dependent stress distributions within electroplated Cu films due to overlying capping layers. Cu films, 0.65 mm thick, plated on conventional barrier and seed layers received a chemical vapor deposited (CVD) SiCxNyHz cap, an electrolessly deposited CoWP layer, or a CoWP layer followed by a SiCxNyHz cap. GIXRD and conventional x-ray diffraction measurements revealed that strain gradients were created in Cu films possessing a SiCxNyHz cap, where a greater in-plane tensile stress of approximately 180 MPa was generated near the film/cap interface as a result of constraint imposed by the SiCxNyHz layer during cooling from the cap deposition temperature. Although Cu films possessing a CoWP cap without a SiCxNyHz layer did not exhibit depth-dependent stress distributions, subsequent annealing introduced stress gradients and increased the bulk Cu stress. However, a thermal excursion to liquid-nitrogen temperatures significantly reduced tensile stresses in the Cu films.
I. INTRODUCTION
The fabrication of Cu-based metallization in microelectronic technology involves numerous thermal excursions associated with the deposition and curing of constituent materials that comprise the back-end-of-line (BEOL). The thermal expansion mismatch between Cu and the underlying Si substrate can induce significant tensile stress in the metallization after these thermal cycles. Current manufacturing procedures use electroplated Cu possessing Ta-based barrier layers that line the trench bottoms and sidewalls as well as capping layers on the top surface to limit interdiffusion between Cu and its environment and to mitigate electromigration along the metallization interfaces. Because tensile stress in the Cu features can facilitate the creation of voids, conditions that accentuate tensile stress must be properly understood and controlled. The presence of passivation layers above blanket Cu films has been shown to reduce a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: Unity Semiconductor, Sunnyvale, CA. This paper was selected as an Outstanding Symposium Paper for the 2009 MRS Spring Meeting, Symposium D Proceedings, Vol. 1156. DOI: 10.1557/JMR.2010.0102 622
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J. Mater. Res., Vol. 25, No. 4, Apr 2010 Downloaded: 13 Mar 2015
stress relaxation at higher temperatures1 by limiting diffusional mechanisms.2 Because the interface between the Cu metallization and capping layers represents a location that is susceptible to electromigration-induced mass flow,3 a decrease in the relaxation of the tensile stress in this region represents a key reliability issue that must be investigated. Glanc
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