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Nanoscale holographic interferometry for strain measurements in electronic devices


Strained silicon is now an integral feature of the latest generation of transistors and electronic devices1,2,3 because of the associated enhancement in carrier mobility4,5. Strain is also expected to have an important role in future devices based on nanowires6 and in optoelectronic components7. Different strategies have been used to engineer strain in devices, leading to complex strain distributions in two and three dimensions8,9. Developing methods of strain measurement at the nanoscale has therefore been an important objective in recent years but has proved elusive in practice1,10: none of the existing techniques combines the necessary spatial resolution, precision and field of view. For example, Raman spectroscopy or X-ray diffraction techniques can map strain at the micrometre scale, whereas transmission electron microscopy allows strain measurement at the nanometre scale but only over small sample areas. Here we present a technique capable of bridging this gap and measuring strain to high precision, with nanometre spatial resolution and for micrometre fields of view11. Our method combines the advantages of moiré techniques12 with the flexibility of off-axis electron holography13 and is also applicable to relatively thick samples, thus reducing the influence of thin-film relaxation effects.

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Figure 1: Principle of the dark-field holographic moiré technique, a combination of the conventional moiré technique and off-axis electron holography.
Figure 2: Dark-field holographic moiré experiment on a strained-silicon transistor array.
Figure 3: Measured deformation of strained-silicon transistor array shown in Fig. 2 .
Figure 4: In-plane deformation maps for transistor array.
Figure 5: Deformation profiles of the transistor array.


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F.H. thanks the CEA-LETI for financial support. This work was partially supported by the European Union through the projects PullNano (Pulling the limits of nanoCMOS electronics, IST-026828) and ESTEEM (Enabling Science and Technology through European Electron Microscopy, IP3: 0260019).We thank P. Mooney for supplying the CCD camera calibration data, P. Verheyen and R. Loo for the device material, and N. Lou and P. Salles for help with FIB preparation.

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Correspondence to Martin Hÿtch.

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Hÿtch, M., Houdellier, F., Hüe, F. et al. Nanoscale holographic interferometry for strain measurements in electronic devices. Nature 453, 1086–1089 (2008).

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