ABSTRACT Strain engineering in the conduction channel is a cost effective method of boosting the ... more ABSTRACT Strain engineering in the conduction channel is a cost effective method of boosting the performance in state-of-the-art semiconductor devices. However, given the small dimensions of these devices, it is difficult to quantitatively measure the strain with the required spatial resolution. Three different transmission electron microscopy techniques, high-angle annular dark field scanning transmission electron microscopy, dark field electron holography, and nanobeam electron diffraction have been applied to measure the strain in simple bulk and SOI calibration specimens. These techniques are then applied to different gate length SiGe SOI pFET devices in order to measure the strain in the conduction channel. For these devices, improved spatial resolution is required, and strain maps with spatial resolutions as good as 1 nm have been achieved. Finally, we discuss the relative advantages and disadvantages of using these three different techniques when used for strain measurement.
ABSTRACT Résumé – De part leurs propriétés intéressantes en termes de mobilités de porteurs, les ... more ABSTRACT Résumé – De part leurs propriétés intéressantes en termes de mobilités de porteurs, les lignes de silicium contraintes peuvent servir de canal dans les transistors. Des méthodes de caractérisations sont nécessaires dans ce type d'applications pour mesurer les contraintes et déformations résiduelles dans les dispositifs. La méthode des Moirés en microscopie électronique en transmission (TEM), la spectroscopie Raman et la diffraction par rayons X sont étudiées ici pour quantifier ces contraintes. Le phénomène de relaxation des contraintes dans les lames minces TEM a été pris en compte à l'aide de simulations par éléments finis. Les résultats très proches entre simulations et expériences ont permis de valider notre approche de mesure de déformations.
We investigate electron vortex beams scattering on chiral crystals. We start by studying point sc... more We investigate electron vortex beams scattering on chiral crystals. We start by studying point scatterers on a helix, were we derive a relation between the handedness of the helix and the topological charge of the electron vortex on one hand, and the symmetry of the Higher Order Laue Zones in the diffraction pattern on the other. We then extend this to atoms arranged on a helix as found in crystals which belong to chiral space groups and propose a new method to determine the handedness of such crystals within the kinematical approximation. The technique avoids the need for dynamical simulations and makes it possible to determine the handedness of extremely thin samples in which multiple scattering is suppressed. In order to verify the model, elastic scattering simulations are performed and an experimental demonstration on Mn2Sb2O7 is given where we find the sample to belong to the right handed variant of the enantiomorphic pair. This technique demonstrates how electron vortex beam diffraction can be used to study chiral materials in transmission electron microscopy. PACS numbers: 61.05.J-, 03.65.Vf, 41.85.-p
By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmiss... more By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a field-induced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented bright-field detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM ...
Quantitative annular dark field scanning transmission electron microscopy (ADF STEM) has become a... more Quantitative annular dark field scanning transmission electron microscopy (ADF STEM) has become a powerful technique to characterise nano-particles on an atomic scale. Because of their limited size and beam sensitivity, the atomic structure of such particles may become extremely challenging to determine. Therefore keeping the incoming electron dose to a minimum is important. However, this may reduce the reliability of quantitative ADF STEM which will here be demonstrated for nano-particle atom-counting. Based on experimental ADF STEM images of a real industrial catalyst, we discuss the limits for counting the number of atoms in a projected atomic column with single atom sensitivity. We diagnose these limits by combining a thorough statistical method and detailed image simulations.
The recent demonstration of electron vortex beams has opened up the new possibility of studying o... more The recent demonstration of electron vortex beams has opened up the new possibility of studying orbital angular momentum (OAM) in the interaction between electron beams and matter. To this aim, methods to analyze the OAM of an electron beam are fundamentally important and a necessary next step. We demonstrate the measurement of electron beam OAM through a variety of techniques. The use of forked holographic masks, diffraction from geometric apertures, diffraction from a knifeedge and the application of an astigmatic lens are all experimentally demonstrated. The viability and limitations of each are discussed with supporting numerical simulations.
In the last five years, a lot of work has been done on the use of CBED HOLZ lines to quantitative... more In the last five years, a lot of work has been done on the use of CBED HOLZ lines to quantitatively measure strain at nanometre scale [1–4]. HOLZ lines splitting have been observed in some situations and were related to stress relaxation in thin TEM lamella [1]. In this study we work further on the origin of HOLZ lines splitting and propose an explanation of lines asymmetry which appears in some experiments [5]. A model system, composed of a 30 nm Si0.7Ge0.3 epitaxial layer embedded in silicon, was experimentally observed (Figure 1a). Part of TEM samples were realized by tripode polishing with such a weak angle (0.5°) that faces can be considered as parallel. Others, presenting asymmetric HOLZ line splitting, were obtained using the SACT method [6]. CBED patterns were recorded on a FEI Titan operating at 300kV and energy filtered with a slit of 10eV in different zone axis ([8,11,0] and [2,3,0]).
Si∕SiGeC superlattices are used in the construction of new generation devices such as multichanne... more Si∕SiGeC superlattices are used in the construction of new generation devices such as multichannel transistors. The incorporation of C in the SiGe layers allows for a better control of the strain and the Ge content. However the formation of β-SiC clusters during annealing at high temperature limits the thermal stability of the alloy. It leads to a strong modification of the strain due to the reduction of the substitutional carbon content. Here, we investigated the behavior of Si∕SiGeC superlattices that have been annealed using different characterization techniques: dark-field electron holography for the evaluation of strain; infrared spectroscopy and ToF-SIMS for the determination of the composition. It was found that after annealing at 1050 °C, the reduction of the substitutional C proportion leads to a recovery of the perpendicular strain in the superlattice. It was also proposed that the local arrangement of C atoms in a third nearest neighbor configuration is an intermediary step during the formation of the SiC clusters.
ABSTRACT We report the structural and compositional nanoscale characterization of InAlN/GaN nanor... more ABSTRACT We report the structural and compositional nanoscale characterization of InAlN/GaN nanoribbon-structured high electron mobility transistors (HEMTs) through the use of geometric phase analysis (GPA) and nanobeam electron diffraction (NBED). The strain distribution in the HEMT layer is quantified and compared to the expected strain profile for the nominal structure predicted by finite element analysis (FEA). Using the experimental strain results, the actual structure is determined and used to modify the FEA model. The improved fit of the model demonstrates that GPA and NBED provide a powerful platform for routine and rapid characterization of strain in III-V semiconducting device systems leading to insights into device evolution during processing and future device optimization.
Ferrite growth kinetics was measured under highly controlled decarburization conditions in an Fe-... more Ferrite growth kinetics was measured under highly controlled decarburization conditions in an Fe-0.94%Mn-0.57%C (mass%) alloy. The observed growth kinetics closely followed the predictions of the local equilibrium non-partitioning (LE-NP) model over the temperature range 725-775°C. A transition from LE-NP to paraequilibrium (PE) kinetics was observed, for the first time, as the temperature was increased from 775°C to 825°C. Long-lived parabolic kinetic states that are intermediate between LE-NP and PE were observed at these intermediate temperatures. Above 825°C, ferrite growth appeared to follow the predictions of the PE model up to the T 0 temperature at which ferrite growth stopped. These novel results are attributed to the segregation of Mn to the moving interface. It is thought that this process has the effect of decreasing the Mn concentration on the austenite side of the interface and, consequently, extending the PE state.
ABSTRACT Strain engineering in the conduction channel is a cost effective method of boosting the ... more ABSTRACT Strain engineering in the conduction channel is a cost effective method of boosting the performance in state-of-the-art semiconductor devices. However, given the small dimensions of these devices, it is difficult to quantitatively measure the strain with the required spatial resolution. Three different transmission electron microscopy techniques, high-angle annular dark field scanning transmission electron microscopy, dark field electron holography, and nanobeam electron diffraction have been applied to measure the strain in simple bulk and SOI calibration specimens. These techniques are then applied to different gate length SiGe SOI pFET devices in order to measure the strain in the conduction channel. For these devices, improved spatial resolution is required, and strain maps with spatial resolutions as good as 1 nm have been achieved. Finally, we discuss the relative advantages and disadvantages of using these three different techniques when used for strain measurement.
ABSTRACT Résumé – De part leurs propriétés intéressantes en termes de mobilités de porteurs, les ... more ABSTRACT Résumé – De part leurs propriétés intéressantes en termes de mobilités de porteurs, les lignes de silicium contraintes peuvent servir de canal dans les transistors. Des méthodes de caractérisations sont nécessaires dans ce type d'applications pour mesurer les contraintes et déformations résiduelles dans les dispositifs. La méthode des Moirés en microscopie électronique en transmission (TEM), la spectroscopie Raman et la diffraction par rayons X sont étudiées ici pour quantifier ces contraintes. Le phénomène de relaxation des contraintes dans les lames minces TEM a été pris en compte à l'aide de simulations par éléments finis. Les résultats très proches entre simulations et expériences ont permis de valider notre approche de mesure de déformations.
We investigate electron vortex beams scattering on chiral crystals. We start by studying point sc... more We investigate electron vortex beams scattering on chiral crystals. We start by studying point scatterers on a helix, were we derive a relation between the handedness of the helix and the topological charge of the electron vortex on one hand, and the symmetry of the Higher Order Laue Zones in the diffraction pattern on the other. We then extend this to atoms arranged on a helix as found in crystals which belong to chiral space groups and propose a new method to determine the handedness of such crystals within the kinematical approximation. The technique avoids the need for dynamical simulations and makes it possible to determine the handedness of extremely thin samples in which multiple scattering is suppressed. In order to verify the model, elastic scattering simulations are performed and an experimental demonstration on Mn2Sb2O7 is given where we find the sample to belong to the right handed variant of the enantiomorphic pair. This technique demonstrates how electron vortex beam diffraction can be used to study chiral materials in transmission electron microscopy. PACS numbers: 61.05.J-, 03.65.Vf, 41.85.-p
By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmiss... more By focusing electrons on probes with a diameter of 50 pm, aberration-corrected scanning transmission electron microscopy (STEM) is currently crossing the border to probing subatomic details. A major challenge is the measurement of atomic electric fields using differential phase contrast (DPC) microscopy, traditionally exploiting the concept of a field-induced shift of diffraction patterns. Here we present a simplified quantum theoretical interpretation of DPC. This enables us to calculate the momentum transferred to the STEM probe from diffracted intensities recorded on a pixel array instead of conventional segmented bright-field detectors. The methodical development yielding atomic electric field, charge and electron density is performed using simulations for binary GaN as an ideal model system. We then present a detailed experimental study of SrTiO3 yielding atomic electric fields, validated by comprehensive simulations. With this interpretation and upgraded instrumentation, STEM ...
Quantitative annular dark field scanning transmission electron microscopy (ADF STEM) has become a... more Quantitative annular dark field scanning transmission electron microscopy (ADF STEM) has become a powerful technique to characterise nano-particles on an atomic scale. Because of their limited size and beam sensitivity, the atomic structure of such particles may become extremely challenging to determine. Therefore keeping the incoming electron dose to a minimum is important. However, this may reduce the reliability of quantitative ADF STEM which will here be demonstrated for nano-particle atom-counting. Based on experimental ADF STEM images of a real industrial catalyst, we discuss the limits for counting the number of atoms in a projected atomic column with single atom sensitivity. We diagnose these limits by combining a thorough statistical method and detailed image simulations.
The recent demonstration of electron vortex beams has opened up the new possibility of studying o... more The recent demonstration of electron vortex beams has opened up the new possibility of studying orbital angular momentum (OAM) in the interaction between electron beams and matter. To this aim, methods to analyze the OAM of an electron beam are fundamentally important and a necessary next step. We demonstrate the measurement of electron beam OAM through a variety of techniques. The use of forked holographic masks, diffraction from geometric apertures, diffraction from a knifeedge and the application of an astigmatic lens are all experimentally demonstrated. The viability and limitations of each are discussed with supporting numerical simulations.
In the last five years, a lot of work has been done on the use of CBED HOLZ lines to quantitative... more In the last five years, a lot of work has been done on the use of CBED HOLZ lines to quantitatively measure strain at nanometre scale [1–4]. HOLZ lines splitting have been observed in some situations and were related to stress relaxation in thin TEM lamella [1]. In this study we work further on the origin of HOLZ lines splitting and propose an explanation of lines asymmetry which appears in some experiments [5]. A model system, composed of a 30 nm Si0.7Ge0.3 epitaxial layer embedded in silicon, was experimentally observed (Figure 1a). Part of TEM samples were realized by tripode polishing with such a weak angle (0.5°) that faces can be considered as parallel. Others, presenting asymmetric HOLZ line splitting, were obtained using the SACT method [6]. CBED patterns were recorded on a FEI Titan operating at 300kV and energy filtered with a slit of 10eV in different zone axis ([8,11,0] and [2,3,0]).
Si∕SiGeC superlattices are used in the construction of new generation devices such as multichanne... more Si∕SiGeC superlattices are used in the construction of new generation devices such as multichannel transistors. The incorporation of C in the SiGe layers allows for a better control of the strain and the Ge content. However the formation of β-SiC clusters during annealing at high temperature limits the thermal stability of the alloy. It leads to a strong modification of the strain due to the reduction of the substitutional carbon content. Here, we investigated the behavior of Si∕SiGeC superlattices that have been annealed using different characterization techniques: dark-field electron holography for the evaluation of strain; infrared spectroscopy and ToF-SIMS for the determination of the composition. It was found that after annealing at 1050 °C, the reduction of the substitutional C proportion leads to a recovery of the perpendicular strain in the superlattice. It was also proposed that the local arrangement of C atoms in a third nearest neighbor configuration is an intermediary step during the formation of the SiC clusters.
ABSTRACT We report the structural and compositional nanoscale characterization of InAlN/GaN nanor... more ABSTRACT We report the structural and compositional nanoscale characterization of InAlN/GaN nanoribbon-structured high electron mobility transistors (HEMTs) through the use of geometric phase analysis (GPA) and nanobeam electron diffraction (NBED). The strain distribution in the HEMT layer is quantified and compared to the expected strain profile for the nominal structure predicted by finite element analysis (FEA). Using the experimental strain results, the actual structure is determined and used to modify the FEA model. The improved fit of the model demonstrates that GPA and NBED provide a powerful platform for routine and rapid characterization of strain in III-V semiconducting device systems leading to insights into device evolution during processing and future device optimization.
Ferrite growth kinetics was measured under highly controlled decarburization conditions in an Fe-... more Ferrite growth kinetics was measured under highly controlled decarburization conditions in an Fe-0.94%Mn-0.57%C (mass%) alloy. The observed growth kinetics closely followed the predictions of the local equilibrium non-partitioning (LE-NP) model over the temperature range 725-775°C. A transition from LE-NP to paraequilibrium (PE) kinetics was observed, for the first time, as the temperature was increased from 775°C to 825°C. Long-lived parabolic kinetic states that are intermediate between LE-NP and PE were observed at these intermediate temperatures. Above 825°C, ferrite growth appeared to follow the predictions of the PE model up to the T 0 temperature at which ferrite growth stopped. These novel results are attributed to the segregation of Mn to the moving interface. It is thought that this process has the effect of decreasing the Mn concentration on the austenite side of the interface and, consequently, extending the PE state.
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Papers by Armand Béché