Copper has become the material of choice for metallisation of microelectronics devices thanks to its high thermal and electrical conductivities. Typically, Cu lines within dielectric trenches are created by electrochemical deposition. Since the thermal expansion coefficient of Cu is higher than for the surrounding materials, thermal cycles during subsequent processing steps often induce high residual stress. Thus, the mechanical integrity of the Cu interconnect remains a major concern. For process optimisation it is necessary to exactly quantify stress in the Cu lines.

X-ray diffraction is a convenient technique for stress measurements in polycrystalline materials. It is non-destructive and it allows one to determine all components of the stress tensor. Measurements are specific for a certain crystalline phase (fcc copper in our case), which is very useful in the case of multi-component samples and complex geometry. However, the major limitation of this technique with laboratory X-ray sources is the spatial resolution, which hardly reaches below a few hundreds micrometres. This is insufficient for stress measurements of today’s devices.

Sub-micrometre measurements have now become possible at the French CRG beamline BM32. A novel setup, utilising the X-rays from a bending magnet, allows investigation of the crystallographic orientations and strain/stress states of heterogeneous crystalline materials below the micrometre scale. Unique in Europe, it combines white and monochromatic beam micro-diffraction, following the method of MacDowell and co-workers [1] at ALS. The white beam from the bending magnet is focussed by mirrors onto an adjustable slit of typically 20 x 20 µm2. This secondary source is further reduced to sub-micrometric dimensions using a pair of Kirkpatrick-Baez mirrors situated just before the sample (Figure 86).

Fig. 86: Microdiffraction setup on the CRG beamline BM32.


This technique allowed the determination of all the components of the strain/stress tensors for a copper grain within a 260 nm wide and 250 nm thick interconnection line. It was scanned with a white (5-25 keV) microbeam and Laue diagrams of individual copper grains, smaller than 1 µm3, have been collected by a CCD camera (Figure 87). Each Laue spot can be associated with a specific grain and lattice plane. As a result, both the orientation and lattice distortion of the copper grains can be deduced, allowing the full strain tensor for each grain to be obtained. However, this requires the “hydrostatic part” of the tensor to be determined by accurately measuring at least one lattice plane spacing of the grain. This is accomplished by switching the beamline optics into monochromatic mode and determining the X-ray energy corresponding to a Laue spot originating from a specific lattice plane.

Fig. 87: Collection of a Laue diagram from a single grain.


Once the full strain tensor has been determined, the complete stress tensor is deduced using the known elastic constants of copper. As an example, a triaxial tensile state of stress has been measured on one grain of the interconnect line:

Principal stresses reach values of few hundreds MPa and the hydrostatic part is 418 MPa. The results are consistent with previous measurements performed at a macroscopic scale on the same kind of device [2].



[1] A.A. MacDowell, R.S. Celestre, N. Tamura, R. Spolenak, B. Valek, W.L. Brown, J.C. Bravman, H.A. Padmore, B.W. Batterman, J.R. Patel, Nuclear Instruments and Methods in Physics Research A, 467-468, 936-943 (2001).
[2] A. Baldacci, C. Rivero, P. Gergaud, M. Grégoire, O. Sicardy, O. Bostrom, P. Boivin, J.S. Micha, O. Thomas, 34th European Solid State Device Research Conference ESSDERC, 20-24 September 2004, Louvain.


O. Sicardy (a), X. Biquard (b), J.S. Micha (c), F. Rieutord (b), O. Robach (b), O. Ulrich (b), O. Geaymond (d), V. Carreau (a).
(a) Direction de la Recherche Technologique, CEA-Grenoble (France)
(b) Département de Recherche Fondamentale sur la Matière Condensée, CEA-Grenoble (France)
(c) UMR Structures et Propriétés d’Architectures Moléculaires, CNRS-Grenoble (France)
(d) Institut Néel, CNRS-Grenoble (France)