Scanning probe microscopy generated out-of-plane deformation maps exhibiting heterogeneous nanoscale deformation resulti
- PDF / 984,491 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 149 Views
Room-temperature scanning probe microscopy was used to generate out-of-plane deformation maps around Cu vias and polyimide mesas in single-level Cu–polyimide damascene interconnect structures subjected to a room-temperature to 350 °C thermal cycle. The deformation maps are obtained by taking the difference between the images obtained before and after thermal processing. The deformation of the Cu is shown to be highly heterogeneous on the submicrometer scale. Direct evidence of Cu–Ta interfacial sliding, Cu–Cu grain boundary sliding, and diffusion creep is presented. The direction of Cu–Ta sliding is shown to depend on polyimide mesa size. A hot-stage atomic force microscope was used to show that hillock/extrusion growth occurs at temperatures between 130 and 180 °C. We propose that this hillock/extrusion growth is correlated with dips in stress–temperature plots for blanket, uncapped Cu films in the same temperature range and that the absence of dips for nitride-capped Cu films is due to suppression of the hillock/extrusion growth.
I. INTRODUCTION
Cu–damascene interconnect structures based on subtractive dielectric processing have been fabricated using a broad variety of polymer and oxide-based dielectrics.1 All of these structures are subjected to multiple thermal cycles from room temperature to somewhere around 350– 400 °C. During this thermal cycle, the Cu, the dielectric, and the liner are all subjected to stresses that arise from their difference in coefficient of thermal expansion with each other and with that of the Si substrate. These stresses impact the reliability of the interfaces, the liner, and the Cu lines and vias and therefore are the subject of extensive analytical and experimental investigations. The deformation of Cu blanket films has been studied to understand the behavior of the Cu component of damascene interconnects. Many investigators have used wafer curvature versus temperature measurements to show that blanket metal films exhibit thermally activated, time-dependent deformation.2,3 Thouless et al.4 suggested that Cu thin films deform by thermally activated glide at temperatures below approximately 300 °C and by grain boundary diffusion creep (Coble creep) at temperatures above this temperature. In a later paper, Thouless et al.5 showed that blanket Cu films exhibit an anomaly in the stress–temperature curve at approximately 100–150 °C only for the first heating cycle. The 3560
http://journals.cambridge.org
J. Mater. Res., Vol. 16, No. 12, Dec 2001 Downloaded: 14 Mar 2015
stress is initially zero at room temperature. As the temperature is increased, the stress in the film initially increases in the compressive direction. However, at approximately 100– 150 °C, the magnitude of the compressive stress decreases with increasing temperature until the temperature reaches approximately 180 °C upon which the compressive stress returns to increasing in magnitude with increasing temperature. This anomaly is not observed in capped Cu films nor is it observed for Al films which are unavoidably capped
