Germain Servanton

Two-dimensional quantitative mapping of arsenic in nanometer-scale silicon devices using STEM EELS―EDX spectroscopy

Field emission gun (FEG) nanoprobe scanning electron transmission microscopy (STEM) techniques coupled with energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS) are evaluated for the detection of the n-type dopant arsenic, in silicon semiconductor devices with nanometer-scale. Optimization of the experimental procedure, data extraction and the signal-to-noise ratio versus electron dose, show that arsenic detection below 0.1% should be possible. STEM EDX and EELS spectrum profiles have been quantified and compared with secondary ion mass spectrometry (SIMS) analyses which show a good agreement. In addition, the arsenic doping level found inside large and small epitaxial devices have been compared using STEM EDX-EELS profiling. The average doping level is found to be similar but variable interface segregation has been observed. Finally, STEM EDX arsenic mapping acquired in a BiCMOS transistor cross-section shows strong heterogeneities and segregation in the epitaxially grown emitter part.

Field mapping with nanometer-scale resolution for the next generation of electronic devices.

In order to improve the performance of todays nanoscaled semiconductor devices, characterization techniques that can provide information about the position and activity of dopant atoms and the strain fields are essential. Here we demonstrate that by using a modern transmission electron microscope it is possible to apply multiple techniques to advanced materials systems in order to provide information about the structure, fields, and composition with nanometer-scale resolution. Off-axis electron holography has been used to map the active dopant potentials in state-of-the-art semiconductor devices with 1 nm resolution. These dopant maps have been compared to electron energy loss spectroscopy maps that show the positions of the dopant atoms. The strain fields in the devices have been measured by both dark field electron holography and nanobeam electron diffraction.

STEM EDX applications for arsenic dopant mapping in nanometer scale silicon devices

In this paper we evaluate sensitivity limits and applications of scanning transmission electron microscopy (STEM) energy-dispersive X-ray (EDX) spectroscopy technique for the mapping of arsenic dopant distribution in nanometer range silicon devices. First we show that lamella radiation damages, generated by the intense focused electron probe at 200 keV, are significantly reduced at 120 keV. This allows to use high electron doses and therefore to improve the EDX sensitivity. The analysis of 45nm nMOS transistor clearly shows the n doped areas and local segregation in gate and spacers.

Boron atomic-scale mapping in advanced microelectronics by atom probe tomography

Two types of industrial transistor technologies have been studied using atom probe tomography (APT). Both 14 nm node high-K metal-oxide-semiconductor field effect transistors (MOSFETs) on ultrathin body and buried oxide and 320 GHz Ft Si/SiGe Heterojunction Bipolar Transistors (HBT) embedded in a 55-nm BiCMOS chip have been analysed and their atomic distribution has been mapped. Due to the limitations of routine characterisation techniques, boron can remain invisible in such nanometric sized structures. Also, size effects can induce differences between the actual device and larger test zones used for monitoring these technologies. This paper presents results obtained by APT from two advanced nodes, in contrast to complementary techniques. Using different methodologies, including specific APT-friendly test structures and multiple-impact data filtering, the dopant behaviour in these structures can be better understood. An unexpected boron distribution in both the MOSFET source/drain and HBT base regions has been highlighted.Two types of industrial transistor technologies have been studied using atom probe tomography (APT). Both 14 nm node high-K metal-oxide-semiconductor field effect transistors (MOSFETs) on ultrathin body and buried oxide and 320 GHz Ft Si/SiGe Heterojunction Bipolar Transistors (HBT) embedded in a 55-nm BiCMOS chip have been analysed and their atomic distribution has been mapped. Due to the limitations of routine characterisation techniques, boron can remain invisible in such nanometric sized structures. Also, size effects can induce differences between the actual device and larger test zones used for monitoring these technologies. This paper presents results obtained by APT from two advanced nodes, in contrast to complementary techniques. Using different methodologies, including specific APT-friendly test structures and multiple-impact data filtering, the dopant behaviour in these structures can be better understood. An unexpected boron distribution in both the MOSFET source/drain and HBT base regions has...

Field Mapping Of Semiconductors In A State‐Of‐The‐Art Electron Microscope

Off‐axis electron holography has been used to measure the strain and the dopant fields in semiconductor specimens that have been prepared for examination by focused ion beam milling. By using the electrical and mechanical stability of the FEI Titan TEM, electron holograms have been acquired for long time periods which leads to active dopant and strain maps with excellent signal to noise ratios. We show that the position of the electrical junction can be measured in these devices specimens with a spatial resolution of 1 nm. In addition, we demonstrate that dark field electron holography and nanobeam electron diffraction can be used to quantitatively measure the strain in a range of specimens from 10‐nm‐thick SiGe layers, SiGe recessed source and drain transistors and CESL pMOS devices. In addition, the evolution of strain during the silicidation process has been observed in SiGe device specimens.

A Comparative Analysis of a Si/SiGe Heterojunction-Bipolar Transistors: APT, STEM-EDX and ToF-SIMS

Due to the complexity of characterising compound semiconductors, including dopant distribution, multiple characterisation techniques are needed. Traditionally time-of-flight secondary ion mass spectroscopy (SIMS) has been the tool of choice for chemical profiling of semiconductor systems. Although it affords a lower limit of detection, it is constrained by a low lateral resolution, making large test zones necessary (several hundred microns). More recently, energy dispersive X-ray scanning transmission electron microscopy (STEM-EDX) allows local specimen preparation and can generate 2D concentration maps. But due to low sensitivity it cannot quantify light elements (i.e. boron). Because of size effects, large test zones are not always representative of the local chemistry in the device and a complete picture is therefore unavailable. Atom probe tomography (APT) is an analytical 3D microscopy technique which maps the position of atoms in a material allowing composition measurements of a small selected volume. With a sub-nanometre spatial resolution, analysis of localised structures is possible and all elements are detected with the same probability. Initially dedicated to metals, semiconductor applications have escalated in recent years [1].

Nano-field mapping for the semiconductor industry

There is a need to measure the dopant potentials and strain fields in semiconductor materials with nm-scale resolution. Here we show that off-axis electron holography is a powerful technique that can be used to measure the fields present in a high-k metal gate 28-nm node nMOS device with a contact etch stop liner stressor. Off-axis electron holography has been used to map the positions of the active dopants with a spatial resolution of 1 nm. The experimental results have been compared to electron energy loss spectroscopy maps. Finally, dark field electron holography has also been used to provide strain maps and the experimental results have been verified using nanobeam electron diffraction.

STEM EELS/EDX dopant analysis of nm-scale Si devices

The mapping of dopant in Si devices is critical for their performance optimisation. Off-axis electron holography is a TEM based technique that is presently used to provide 2D dopant maps of semiconductor devices [1]. Due to the improvement of electron gun brightness and probe aberration correctors in TEM, the direct detection of dopant atoms is now possible. In this paper we demonstrate dopant profiling using either 200 keV low-dose EELS or 120 keV high-dose EDX. Our results are compared with SIMS.