Jean-Paul Barnes

Strain measurement at the nanoscale: Comparison between convergent beam electron diffraction, nano-beam electron diffraction, high resolution imaging and dark field electron holography.

Convergent beam electron diffraction (CBED), nano-beam electron diffraction (NBED or NBD), high resolution imaging (HRTEM and HRSTEM) and dark field electron holography (DFEH or HoloDark) are five TEM based techniques able to quantitatively measure strain at the nanometer scale. In order to demonstrate the advantages and disadvantages of each technique, two samples composed of epitaxial silicon-germanium layers embedded in a silicon matrix have been investigated. The five techniques are then compared in terms of strain precision and accuracy, spatial resolution, field of view, mapping abilities and ease of performance and analysis.

Dark field electron holography for quantitative strain measurements with nanometer-scale spatial resolution

Strain measurements on strained SiGe specimens have been performed using dark field electron holography. By combining the excellent stability of state-of-the-art electron microscopes with careful specimen preparation we have been able to acquire two-dimensional strain maps of the layers with a spatial resolution of 5 nm, a background noise of 2×10−4, an interference width of 1500 nm, and a field of view of more than 500×500 nm2. We also show that the strain measurements are quantitative to within experimental error.

3D analysis of advanced nano-devices using electron and atom probe tomography.

The structural and chemical properties of advanced nano-devices with a three-dimensional (3D) architecture have been studied at the nanometre scale. An original method has been used to characterize gate-all-around and tri-gate silicon nanowire transistor by combining electron tomography and atom probe tomography (APT). Results show that electron tomography is a well suited method to determine the morphological structure and the dimension variations of devices provided that the atomic number contrast is sufficient but without an absolute chemical identification. APT can map the 3D chemical distribution of the atoms in devices but suffers from strong distortions in the dimensions of the reconstructed volume. These may be corrected using a simple method based on atomic density correction and electron tomography data. Moreover, this combination is particularly useful in helping to understand the evaporation mechanisms and improve APT reconstructions. This paper demonstrated that a full 3D characterization of nano-devices requires the combination of both tomography techniques.

Dark field electron holography for strain measurement

Dark field electron holography is a new TEM-based technique for measuring strain with nanometer scale resolution. Here we present the procedure to align a transmission electron microscope and obtain dark field holograms as well as the theoretical background necessary to reconstruct strain maps from holograms. A series of experimental parameters such as biprism voltage, sample thickness, exposure time, tilt angle and choice of diffracted beam are then investigated on a silicon-germanium layer epitaxially embedded in a silicon matrix in order to obtain optimal dark field holograms over a large field of view with good spatial resolution and strain sensitivity.

Carrier mobility degradation due to high dose implantation in ultrathin unstrained and strained silicon-on-insulator films

Based on electrical measurements and transmission electron microscopy (TEM) imaging, we propose an explanation for the electron and hole mobility degradation with gate length reduction in metal–oxide–semiconductor field effect transistors (MOSFETs). We demonstrate that ion implantation, normally used for source/drain doping, is responsible for transport degradation for short-channel devices. Implantation impact on electrons and holes mobility was investigated both on silicon-on-insulator (SOI) and tensile strained silicon-on-insulator (sSOI) substrates. Wafers with ultrathin Si films (from 8 to 35 nm) were Ge implanted at 3 keV and various concentrations (from 5×1014 to 2×1015 atoms cm−2), then annealed at 600 °C for 1 h. Secondary ion mass spectrometry enabled us to quantify the Ge-implanted atoms concentrations. The end-of-range defects impact on mobility was investigated with the pseudo-MOSFET technique. Measurements showed a mobility decrease as the implantation dose increased. We demonstrated that sS...

Three dimensional imaging and analysis of a single nano-device at the ultimate scale using correlative microscopy techniques

The analysis of a same sample using nanometre or atomic-scale techniques is fundamental to fully understand device properties. This is especially true for the dopant distribution within last generation nano-transistors such as MOSFET or FINFETs. In this work, the spatial distribution of boron in a nano-transistor at the atomic scale has been investigated using a correlative approach combining electron and atom probe tomography. The distortions present in the reconstructed volume using atom probe tomography have been discussed by simulations of surface atoms using a cylindrical symmetry taking into account the evaporation fields. Electron tomography combined with correction of atomic density was used so that to correct image distortions observed in atom probe tomography reconstructions. These corrected atom probe tomography reconstructions then enable a detailed boron doping analysis of the device.

Specifications for hard condensed matter specimens for three-dimensional high-resolution tomographies.

Tomography is a standard and invaluable technique that covers a large range of length scales. It gives access to the inner morphology of specimens and to the three-dimensional (3D) distribution of physical quantities such as elemental composition, crystalline phases, oxidation state, or strain. These data are necessary to determine the effective properties of investigated heterogeneous media. However, each tomographic technique relies on severe sampling conditions and physical principles that require the sample to be adequately shaped. For that purpose, a wide range of sample preparation techniques is used, including mechanical machining, polishing, sawing, ion milling, or chemical techniques. Here, we focus on the basics of tomography that justify such advanced sample preparation, before reviewing and illustrating the main techniques. Performances and limits are highlighted, and we identify the best preparation technique for a particular tomographic scale and application. The targeted tomography techniques include hard X-ray micro- and nanotomography, electron nanotomography, and atom probe tomography. The article mainly focuses on hard condensed matter, including porous materials, alloys, and microelectronics applications, but also includes, to a lesser extent, biological considerations.

Strain mapping with nm-scale resolution for the silicon-on-insulator generation of semiconductor devices by advanced electron microscopy

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.

Experimental off-axis electron holography of focused ion beam-prepared Si p-n junctions with different dopant concentrations

Silicon p-n junction specimens with a range of dopant concentrations have been prepared using focused ion beam milling for examination by off-axis electron holography. Here we show that phenomenon such as the electrically “inactive” thickness is strongly dependent on the dopant concentration of the specimens. We also show a dependence on both the specimen geometry and intensity of the electron beam on the phases measured across the junctions and a good reproducibility of results if care is taken during examination.

Characterization and modeling of structural properties of SiGe/Si superlattices upon annealing

Stacked multichannel or nanowire CMOS transistors are foreseen as viable options in future technology nodes. Superior electric performances and a relative immunity to short channel effects have already been demonstrated in such devices. They rely on (i) the epitaxy of SiGe/Si superlattices, (ii) the anisotropic etching of the source and drain (S/D) blocks and the channels, and (iii) the high degree of selectivity that can be achieved when laterally etching the SiGe sacrificial layers. The voids left by the removal of SiGe are then conformally filled by HfO2/TiN/poly-Si gates, leading to the formation of multichannel devices. Doping elements can be included in situ in the SiGe layers during the epitaxial step in order to achieve a proper S/D doping after annealing. Precise knowledge of the diffusion behavior of all species is then crucial to understand and tailor final device performance. In this work, we investigated the properties of intrinsic or in situ doped (with B, C, or P) SiGe/Si superlattices upon...