Thesis presented October 13, 2009

Abstract:
This work focuses on the study of strain in nanoscaled materials. For the last ten to fifteen years, the development of new structural materials and devices for the microelectronic industry has required the control of strain at these small scales. The needs for characterizations have increased with more demanders criteria on both the spatial resolution and the strain sensitivity. The development and improvement of techniques to fulfill these criteria is therefore necessary. The transmission electron microscope (TEM) is one of the only tools able to measure quantitative strain with nanoscale resolution. Four different TEM techniques have been studied : Moirés technique, convergent beam electron diffraction (CBED), nanobeam electron diffraction (NBED) and dark field electron holography. The availability of a state-of-the-art FEI Titan microscope has allowed useful results to be obtained for each of the techniques studied. These techniques have been investigated in term of spatial resolution, strain sensitivity, technical limitations, microscope configuration, operational mode and constraints they impose for sample preparation. The Moirés technique holds a spatial resolution of about 20 nm with a strain sensitivity of 4x10-4 but requires samples with reference material superimposed with the region of interest. CBED offers the best resolution (1 to 2 nm) with excellent sensitivity (2.10^-4). However, this technique is sensitive to the inhomogeneities in the displacement field along the electron beam direction what leads to apparition of splitting within the diffraction pattern and makes this technique difficult to use in a general way. NBED is probably one of the easiest techniques and usable on most samples. It has a reasonably good spatial resolution (up to 3 nm) but a limited strain sensitivity (6.10^-4) in the best cases. Finally, dark field holography, very recently developed technique, offers a good resolution (around 4 or 5 nm) with an excellent strain sensitivity (2.10^-4). These four techniques have been compared by mapping the strain on both calibrated and test device structures.

Keywords:
Transmission electron microscopy (TEM), Strain, Stress, Convergent beam (CBED), Dark field electron holographie

On-line thesis.