Water at the hydrophilic direct bonding interface
The microelectronics industry is making increasing use of hydrophilic direct bonding technology to produce innovative substrates and components. CEA LETI's teams have been leaders in this field for over 20 years, offering scientific and technological studies on the subject.
The key role of water at the bonding interface can be newly understood thanks to a characterization technique developed at CEA LETI. The aim of this thesis is to confirm or refute the physico-chemical mechanisms at play at the bonding interface, depending on the surface preparations and materials in contact.
A large part of this work will be carried out on our cleanroom tools. The characterization of surface hydration using this original technique will be complemented by standard characterizations such as adhesion and adherence energy measurements, FTIR-MIR and SIMS analyses, and X-ray reflectivity at ESRF.
3D chemical analysis of downscaled ePCM devices for sub-18 nm technology nodes using STEM-EDX tomography and machine learning tools
The context of this PhD is the recent progress of Phase-Change Memory technology in the embedded applications (ePCM). The ultimate scaling of ePCM for sub-18nm nodes poses many challenges not only in fabrication, but also in the physico-chemical characterization of these devices. The aim of the project is to study the 3D chemical segregation/crystallization phenomena in new PCM alloys integrated into planar and vertical ePCM scaled devices, using electron tomography in STEM-EDX (and 4D-STEM) mode. Given the extreme downscaling and the complex geometry of the devices, the focus will be on optimizing experimental conditions and applying machine learning and deep learning techniques to improve the quality and reliability of the obtained 3D results. A correlation with the device electrical behavior will be carried out to better understand the phenomena behind failures after endurance and after data loss at high temperatures.
A probe-corrected Cold-FEG NeoARM TEM (60kV-200kV) will be used for the tomographic data acquisition. It is equipped with two large solid angle SSD detectors (JEOL Centurio), a CEOS Energy-Filtering and Imaging Device (CEFID) and a Timepix3 direct electron camera. The candidate will also have access to in-house Python codes as well as to the computing resources needed to carry out the spectral and tomographic data analysis.
Development of algorithms and modeling tools of Low-Energy Critical Dimension Small Angle X-ray Scattering
This PhD will take place at the CEA–LETI, a major European actor in the semiconductor industry, and more precisely, at the Nanocharacterization platform of the CEA–LETI witch offer world-class analytical techniques and state-of-the-art instruments. Our team aims to accompany the industry in the development of new characterization tools and so to meet the metrological needs of future technological nodes. Over the past few years, pioneer developments on a new metrology technique based on hard x-ray scattering called CD-SAXS were done at the PFNC. This technique is used to reconstruct the in-plane and out-of-plane structure of nanostructured thin-films with a sub-nm resolution. In this project, we are looking to extend the CD-SAXS approach leveraging the recent breakthrough in the development of low-energy x-ray sources (A. Lhuillier et al. 1988, Nobel prize 2023) called High Harmonics Generation (HHG) sources. Therefore, you will participate in the development of a new and promising characterization methods called Low-energy critical dimension small angle x-ray scattering. The very first proof of concept of this new measurement was conducted in November 2023.
Mission:
In order to include in the data reduction the measurement specificities of this new approach (multi-wavelength, low energy, …) your mission will focus on several aspects to explore in parallel:
- Develop new modeling tools to analyze the data:
o Finite element simulations with Maxwell solver
o Analytical Fourier Transform (similar to standard CD-SAXS) vs dynamical theory
o Comparison between the two approaches
- Build new models dedicated to lithography problematic (CD, overlay, roughness)
- Define the limitations of the technique through the simulation (in term of resolution (nm), uncertainty)
This work will support the development of CD-SAXS measurements with a laboratory HHG (High Harmonic Generation) source lead by a Postdoctoral fellow.
Thermomechanical study of heterostructures according to bonding conditions
For many industrial applications, the assembly of several structures is one of the key stages in the manufacturing process. However, these steps are generally difficult to carry out, as they lead to significant increases in warpage. Controlling stresses and strains generated by heterostructures is however imperative. We proposes to address this subject using both experimental exploration and simulation through thermomechanical studies in order to predict and anticipate problems due to high deformations.
Optimisation of advanced mask design for sub-micrometer 3D lithography
With the advancement of opto-electronic technology, 3D patterns with sub micrometer dimensions are more and more integrated in the device, especially on imaging and AR/VR systems. To fabricate such 3D structures using standard lithography technique requires numerous process steps: multiple lithography and pattern transfer, which is time and resource consuming.
With optical grayscale lithography, such 3D structures can be fabricated in single lithography step, therefore reducing significantly the number of process steps required in standard lithography. For high volume manufacturing of such 3D patterns, optical grayscale lithography with Deep-UV (DUV), 248nm and 193nm are the most relevant, as it is compatible with industrial production line. This technique of 3D lithography is however more complex than it seems, which requires advance lithography model and data-preparation flow to design optical mask corresponding to the desired 3D pattern.
Advanced Surface Analysis of Ferroelectrics for memory applications
CEA-Leti has a robust track record in memory technology. This PhD project aims to contribute to the development of HfO2-based ferroelectric devices. One of the major challenges in this field is to stabilize the orthorhombic phase while reducing film thickness and thermal budget. To gain a deeper understanding of the underlying mechanisms, a novel sample preparation method will be adapted from a previous PhD project and further developed for application to ferroelectric memories. This method involves creating a beveled crater that exposes the entire thickness of the film, allowing for access by multiple characterization techniques (XPS, TOF-SIMS, SPM) on the same area. This approach will enable the correlation of compositional and chemical measurements with electrical properties. Furthermore, heating and biasing within advanced surface characterization instruments (TOF-SIMS, XPS) will provide insights into how device performance is influenced by compositional and chemical changes.
You possess strong experimental skills and a keen interest in state-of-the-art surface analysis instruments. You excel in team environments and will have the opportunity to collaborate with experts across a wide range of techniques on the nanocharacterization platform, including advanced numerical data treatment. Proficiency in Python or similar programming languages is highly desirable.
Low temperature selective epitaxial growth of SiGe(:B) for pMOS FD-SOI transistors
As silicon technologies for microelectronics continue to evolve, processes involved in device manufacturing need to be optimized. More specifically, epitaxy, a crystal growth technique, is being used to fabricate 10 nm technological node FD-SOI (Fully Depleted-Silicon On Insulator) transistors as part of CEA-Leti's NextGen project. Doped and undoped Si and SiGe semiconductor epitaxy is being developed to improve the devices' electrical performances. The thesis will focus on selective SiGe(:B) epitaxy for channels and source/drains of pMOS transistors. A comparison of SiGe and SiGe:B growth kinetics will be made between growth under H2, the commonly used carrier gas, and N2. Innovative cyclic deposition/etching (CDE) strategies will also be evaluated, with the aim of lowering process temperatures.
ALD materials for FE and AFE capacitances
Ultrathin HfO2-based materials are regarded as promising candidates for embedded non-volatile memory (eNVM) and logic devices. The CEA-LETI has a leadership position in the field of BEOL-FeRAM memories ultra-low consumption (<100fj/bit) at low voltage (<1V). In this context, the developments expected in this thesis aim to evaluate the impact of HfO2-based ferroelectric FE and antiferroelectric AFE layers (10 to 4 nm fabricated by Atomic Layer Deposition ALD) on the FeRAM properties and performances.
In particular, the subject will permit a deep understanding of the crystallographic phases governing the FE/AFE properties using advanced measurements techniques offered by the CEA-LETI nano-characterization platform (physico-chemical, structural and microscopy analysis, electrical measurements). Several integration solutions for ferroelectric capacitances FeCAPs using ALD FE/AFE layers will be studied including doping, interface layers, sequential fabrication w/wo air break…
Thus, the developments based on FeCAPs stack fabricated using 300mm ALD deposition tool aspires to explore the following items:
1-Doping incorporation in FE/AFE layers (La, Y…)
2-Engineering of the interface between FE/AFE layers and top/bottom electrode
3-Plasma in-situ treatment of bottom electrode surface
4-Sequential deposition with and without air break
[1] S. Martin et al. – IEDM 2024
[2] Appl. Phys. Lett. 124, 243508 (2024)
SCO&FE ALD materials for FeFET transistors
Ferroelectric Field Effect Transistors FeFET is a valuable high-density memory component suitable for 3D DRAM. FeFET concept combines oxide semiconductors SCO as canal material and ferroelectric metal oxides FE as transistor gate [2, 3]. Atomic layer deposition ALD of SCO and FE materials at ultrathin thickness level (<10 nm) and low temperature (10 cm2.Vs); ultrathin (<5nm) and ultra-conformal (aspect ratio 1:10). The PhD student will beneficiate from the rich technical environment of the 300/200mm CEA-LETI clean-room and the nano-characterization platform (physico-chemical, structural and microscopy analysis, electrical measurements).
The developments will focus on the following items:
1-Comparison of SCO layers (IGZO Indium Gallium Zinc Oxide) fabricated using ALD and PVD techniques: implementation of adapted mesurements techniques and test vehicles
2-Intrinsec and electrical characterization of ALD-SCO (IWO, IGZO, InO) and ALD-EF (HZO) layers: stoichiometry, structure, resistivity, mobility….
3-Co-integration of ALD-SCO and ALD-FE layers for vertical and horizontal 3D FeFET structures
[1]10.35848/1347-4065/ac3d0e
[2]https://doi.org/10.1109/TED.2023.3242633
[3]https://doi.org/10.1021/acs.chemmater.3c02223
Direct metal etch mechanisms study for the BEOL of ultimate SOI nodes
The topic fits into the deployment of silicon technologies at the European level (European chips act), led by CEA-Leti. The focus will be on providing advanced technological building blocks for electrical routing (Back End of Line) of logic and analog devices. The development of increasingly high-performance circuits requires interconnections with more aggressive dimensions. The use of traditional routing materials such as copper is therefore being questioned, as is the conventional back-end of line (BEOL) architecture. This thesis topic will address a breakthrough approach, necessary to achieve these ultimate dimensions.
The objective of this PhD is to develop a BEOL technological building block for the advanced SOI (Silicon on Insulator) nodes through a direct metal etching approach. After a preliminary simulation of the electrical properties of interconnections made with different metals, the work will consist in proposing and implementing an innovative integration. In the first phase, the task will be to determine the design of the electrical test structures and establish an integration scheme. In the second phase, the research work will focus on studying the direct etching of the selected metal using sustainable processes while maintaining the performance of both the processes and the final device. The candidate will be able to rely on the eco-innovation team to perform a comparative life cycle analysis (LCA) of this building block.
The PhD contract is for a duration of 3 years and the research work will take place in the clean rooms of CEA-Leti. To successfully carry out this study, the candidate will have access to state-of-the-art equipment and a cutting-edge work environment.