Height Dependent Resistivity of Copper Interconnects in the Size Effect
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0990-B09-08
Height Dependent Resistivity of Copper Interconnects in the Size Effect Hideki Kitada1, Takashi Suzuki2, Takahiro Kimura2, and Tomoji Nakamura1 1
Fujitsu Laboratories Ltd, 10-1 Morinosato-Wakamiya, atsugi, 243-0197, Japan
2
Fujitsu Laboratories Ltd, 50 Fuchigami, Akiruno, 197-0833, Japan
ABSTRACT We investigated the copper grain size dependence on the interconnect line height using the EBSD (Electron Back Scattering Diffraction) pattern method. In our grain size measurements, we excluded the twin boundaries because of its small contribution to the electron scattering. Our experiments showed that the average grain size of a 70 nm-high line was about 24% smaller than for a 190 nm-high line. We estimated the grain boundary scattering components by the Fuchs-Sondheimer (FS) and the Mayadas-Shatzkes (MS) models including the line height dependence of the grain size parameter (d). In order to evaluate precisely the influence of height dependence of grain size in the FS and MS models, we also determined the surface scattering coefficient of the Ta/Cu and SiC/Cu interfaces by an independent experiment. From this, we found that grain boundary scattering components became approximately 32% larger for the 70 nm-wide line when the line height dependence of the grain size was taken into consideration. INTRODUCTION Recently, the scale of LSI devices has reached the applicable limit of Moore's Law. For the LSI interconnects, the electric resistivity of the metal line has increased with the shrinking of the line width and/or height; i.e., the so-called size effect. This new phenomenon brings more RC delay through the incremental resistivity and imposes a loss on the scaling advantage of the device. Therefore, in order to forecast the performance of next generation LSI devices, it is important to understand the size effect. In order to explain the size effect of thin film resistivity, the surface scattering and the grain boundary scattering phenomena are taken into consideration in the Fuchs-Sondheimer (FS) and Mayadas-Shatzkez (MS) models [1-3]. Recently, many reports have appeared that apply the FS and the MS approaches to the copper line used in LSI devices [4-13]. In general, the average copper grain size has become smaller with the scaling of the line size, so the relative contribution from the scattering of the grains becomes large. It is a well-known fact that grain growth in the copper damascene process is heavily influenced by the
line size, geometry and process conditions such as post-plating annealing [14,15]. Therefore it is important to understand the line-width and the line-height dependences of the grain size in order to understanding the size effect. In discussions of the size effect on the copper line, although there are many papers consider the line-width dependence of the grain size [4-13], there is only one previous report that has considered the influence of the line-height dependence of the grain size distribution in the height direction [16]. However, in that paper [16], the influence of the
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