Stress Gradients Observed in Cu Thin Films Induced by Capping Layers
- PDF / 164,914 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 49 Downloads / 171 Views
1156-D05-04
Stress Gradients Observed in Cu Thin Films Induced by Capping Layers Conal E. Murray1, Paul R. Besser2, Christian Witt3, Jean L. Jordan-Sweet1 1
IBM T.J. Watson Research Center, Yorktown Heights, NY. 2
3
GLOBALFOUNDRIES, Inc., Sunnyvale, CA.
GLOBALFOUNDRIES, Inc., T.J. Watson Research Center, Yorktown Heights, NY.
ABSTRACT 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. 0.65 μm thick Cu films plated on conventional barrier and seed layers received a 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 was generated near the film / cap interface. The constraint imposed by the SiCxNyHz layer during cooling from the cap deposition temperature led to an increase in the in-plane stress of approximately 180 MPa from the value measured in the bulk Cu. However, Cu films possessing a CoWP cap without a SiCxNyHz layer did not exhibit depth-dependent stress distributions. Because the CoWP capping deposition temperature was much lower than that employed in SiCxNyHz deposition, the Cu experienced elastic deformation during the capping process. Crosssectional transmission electron microscopy indicated that the top surface of the Cu films exhibited extrusions near grain boundaries for the samples undergoing the thermal excursion during SiCxNyHz deposition. The conformal nature of these caps confirmed that the morphological changes of the Cu film surface occurred prior to capping and are a consequence of the thermal excursions associated with cap deposition. 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 employ 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 stress relaxation at higher temperatures [1] by limiting diffusional mechanisms [2]. Since 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 ten
Data Loading...
