On-line Topography and High Resolution Diffraction with Coherent Illumination Applied for Microelectronics Structures

Drakopoulos¹, I. Snigireva¹, N. Awaji², M. A. Snigirev¹

¹ ESRF, B.P. 220, 38043 Grenoble Cedex, France
² Fujitsu Laboratories Ltd, 10-1 morinosato-Wakamiya, Atsugi 243-01, Japan

Keywords: high resolution diffraction, strain analysis, microelectronics

Phase contrast imaging and tomography of practically transparent purely phase objects with an in-line holography setup using the coherent properties of the beam at third generation synchrotron radiation sources recently was proposed and is widely used [1,2]. The small fluctuations of the object structure or weak deformation fields near surface can be easily localized by means of phase contrast imaging. This technique was applied for phase mapping of the domain structure of a ferroelectric material like lithium niobate [3].

In this paper we would like to report a technique which combines topography and rocking curve mappings for sub-micrometer imaging and strain deformation analysis of microelectronics structures. Cu - patterned industrial silicon (100) wafer consisting of several line arrays of 0.3 to 1.5 mm thickness was studied. The experiment was carried out at the undulator beamline ID22 at the ESRF. The vertical source size of 25 mm (FWHM) located at 45 m from the sample gives us enough spatial coherence. The sample was set in such a way that the Cu-lines were horizontally and so orthogonal to the smallest source dimension. A double crystal Si (111) monochromator was used to select 12 keV X-ray radiation. The sample was mounted on a x-y translation stage of a six-circle diffractometer to allow mapping of the copper pattern. The high-resolution X-ray images were taken using the Bragg 004 reflection. The reflected beam was observed with a high-resolution imaging camera, which has a resolution of 0.7 mm [4]. The wafer was rocked around its reflection angle in a range of 0.005 degree in 0.0005 degree steps and images were recorded at each angle. Such set of images was taken at sample-detector distances of 40 and 120 mm. Also KODAK high-resolution film images were taken at the center of the rocking curves at both distances.

From this experiment we can abstract different results. The horizontal Cu-lines are clearly resolved even at 40 mm distance. With increasing distance a holographic pattern from this lines can be seen. Deformations around the Cu - lines can be easily evaluated from recorded holograms. Local rocking curves from areas of interest on the sample can be extracted using the full set of images and by integrating the local intensities for each angular position. With this one can study the deformation inside the defined regions. A full spatial mapping of rocking curves can be revealed to give deeper insight in the spatial distribution of strains of the patterned wafer.

We want to introduce this new technique as a powerful tool to obtain reciprocal space information with a local resolution in micrometer scale simultaneously for the hole sample in a very short time. As well the visualization of the spatial progression of deformations leads to immediate understanding of involved processes. This new technique therefor should be of great interest in the field of microelectronics and related subjects.

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