Contribution of metal-semiconductor interfaces to the operation of the latest generation of infrared photodiodes
This thesis concerns the field of cooled infrared detectors used for astrophysical applications. In this field, the DPFT/SMTP (Infrared Laboratory) of CEA-LETI-MINATEC works closely with Lynred, a world leader in the production of high-performance infrared focal planes. In this context, the infrared laboratory is developing new generations of infrared detectors to meet the needs of future products.
One of the current development axes concerns the quality of the p-type semiconductor metal interface. These developments are driven by the increase in the operating temperature of the detectors, as well as by the very strong performance requirements for space applications.
The challenge of this thesis is to contribute to a better understanding of the chemical species present at the interface of interest as a function of different surface treatment types and to link them to the electrical properties of the contact made.
The candidate will join the infrared laboratory, which includes the entire detector production process. He/she will produce these samples using the technological means available in the LETI clean room, in collaboration with experts in the field. He/she will also have access to the necessary characterization tools (SIMS, XPS, AFM…) available on the nano-characterization platform (PFNC) or in the CEA clean room. Finally, he/she will be involved in the electro-optical characterization of the material, in collaboration with the Cooled Infrared Imaging Laboratory (LIR), which specializes in fine material characterization.
Development of deposit/etch processes for SADP integration to FD10 node
Developement of new technologic nodes involves both a pattern dimension shrink and a pattern density increase. For the last years, development of multi-Patterning strategies with in particular Spacer Patterning (also called SADP) has signifcantly increased. This approach is based on a sacrificial pattern on which a material is depsosited with a conformal configuration to be etched and thus to define spacers used as masks to pattern the sublayer after sacrificial pattern removals. One of the main challenges of this intergration is the material choice in terms of compatibility (thermal budget, selectivity, etc.). Using SiCo(N)-based materials could be a favourable alternative to standard dielectrics (SiO2, SiN). Another challenge is to achieve only one population after SADP : to prevent microloading effects, etching process with an atomic controlwill be developped (ex. pulsing, ALE, etc.). Environmental footprint should be considered during these process developments.
The purpose of this thesis is to set an integration flow with SiCO(N)-based materials, to developp these materials and to determine associated etching strategies.
To lead your research activity, you would be able to benefit privileged environment offered by CEA-Leti with state of the art tool for process development and for material characterization
Scatterometry measurement of the exposure focal length of photolithography tools
Since the late 2000s with the advent of 45nm CMOS nodes, the control of critical dimensions (CD) of the structures in the photolithography stage has become critical to the reliability of printed circuit boards. Optical photolithography remains the most economical and widespread technique for high volume production in the semiconductor industry. For this type of equipment, manufacturers have focused on increasing the numerical aperture of the exposure lens, reducing sources of optical aberrations and on metrology to ensure efficient monitoring of their machines. These developments were possible at the expense of the depth of field of the exposure. To avoid altering the images transferred to the photosensitive resins, and ultimately have a device failure, it is essential to give a value as accurate and precise as possible of this size. To meet the growing needs of process control and lithography tools required by the most advanced technologies, metrology techniques based on analysis of reflected signals are massively used. Although this methodology is well suited to current CMOS technologies (CMOS14nm and earlier), it is unlikely to address more advanced technologies, so other techniques must emerge, such as techniques based on the analysis of the diffracted signal (scatterometry).
Innovative dry etching process of exotic materials
The advantageous properties (electro-optical, - acoustic, -mechanical) of new materials such as Sc-doped ALN, LNO, LTO or KNN make them essential to meet the development needs of integrated optics, RF telecommunication and microsystems. The production of patterns with submicron dimensions with a significant etch rate (>100nm/min), a vertical profile and a reduced roughness of the pattern's sidewalls are the main goals of the thesis work so as to satisfy the performance criteria of the devices targeted at the application level.
In situ study of the impact of the electric field on the properties of chalcogenide materials
Chalcogenide materials (PCM, OTS, NL, TE, FESO, etc.) are the basis of the most innovative concepts in microelectronics, from PCM memories to the new neuromorphic and spinorbitronic devices (FESO, SOT-RAM, etc.). Part of their operation relies on out-of-equilibrium physics induced by the electronic excitation resulting from the application of an intense electric field. The aim of this thesis is to measure experimentally on chalcogenide thin films the effects induced by the intense electric field on the atomic structure and electronic properties of the material with femtosecond (fs) time resolution. The 'in-operando' conditions of the devices will be reproduced using a THz fs pulse to generate electric fields of the order of a few MV/cm. The induced changes will then be probed using various in situ diagnostic methods (optical spectroscopy or x-ray diffraction and/or ARPES). The results will be compared with ab initio simulations using a state-of-the-art method developed with the University of Liège. Ultimately, the ability to predict the response of different chalcogenide alloys on time scales fs under extreme field conditions will make it possible to optimise the composition and performance of the materials (e- switch effect, electromigration of species under field conditions, etc.), while providing an understanding of the underlying fundamental mechanisms linking electronic excitation, evolution and the properties of the chalcogenide alloys.
“Remote epitaxy" of Cd(Hg)Te
A new way of considering epitaxy has recently appeared thanks to the development of 2D materials. Whereas conventional epitaxy involving covalent bonds is limited in particular to a lattice parameter matching between the substrate and the epitaxial membrane, it appears that this constraint can be significantly released if the epitaxial growth is done by van der Waals interactions. 2D materials are ideal candidates for this type of growth since their surface does not have hanging bonds.
"Remote epitaxy" is a recent innovative and original approach that consists in cutting the classical covalent epitaxial growth by inserting a sheet of 2D material to allow the transmission of the “crystalline field” between the substrate and the epitaxial layer. The stress in the first epitaxial layers is then significantly reduced with the possibility of easily exfoliate and release (thanks to the low energy interface) the epitaxial membrane from its substrate.
This approach has been successfully used in the case of III-V materials with the intercalation of a graphene sheet. We propose in this thesis to study the “remote epitaxy” of II-VI semiconductors, CdTe and HgCdTe that are at the heart of many applications areas such as infrared detection and imaging, X-ray detection and medical applications or photovoltaic.
Several 2D materials will be studied, either reported or directly grown on the surface of the substrate. Graphene will be transferred by dry-method to generate clean interfaces. Preferably, 2D material will be directly grown on the substrate surface. This study will be done in collaboration with the 2D SPINTEC team.
Anisotropies and deformations induced by doping in the latest generation of infrared photodiodes
This thesis concerns the field of HgCdTe infrared detectors for astrophysical applications, for which the Infrared Laboratory of CEA -Leti is one of the world leaders.
The candidate will join the infrared laboratory, which includes the entire detector production process. As a participant in all discussions on the development of CdHgTe samples, he will produce them using the technological means of elaboration available in the Leti clean room, in collaboration with experts in the field.
These samples will then be characterized using our access to synchrotron radiation from ESRF as well as the nano-characterization platform of CEA-Grenoble equipped with a set of state-of-the-art characterization techniques. By studying the changes induced by variations in the sample preparation process using Laue micro-diffraction and SEM-EDX, simultaneous 2D mapping at a submicron scale of local stress and chemical composition will be accessed.
The challenge of this thesis will be to analyse the correlations between chemical composition and local stress, in relation to the specificities of the preparation process. The objective will be to study the mechanisms behind anisotropic behaviour in the structures of interest.
Study of InP and AsGa wafer bonding mechanisms
Direct bonding consists of bringing sufficiently smooth and clean surfaces into contact, in order to create adhesion between them without adding any external material. This technology presents many advantages for the production of stacked structures for microelectronics and micro-technologies and has given rise to numerous innovations (manufacturing of SOI by SmartCutTM, manufacturing of SmartSiCTM, production of MEMS, wafer level packaging, 3D integration, etc.). Today, the rise of photonic technologies and the development of direct die-to-wafer bonding are paving the way for the integration of materials such as InP and GaAs in the world of silicon. In order to push these developments we wish to study the bonding mechanisms of these materials which have not yet been established in the literature.
The thesis will consist of studying the direct bonding mechanisms of InP and GaAs wafers:
A first part of the study will consist of finely characterizing the surface of these materials during pre-bonding preparations (type of bonds created, type of oxide, quantity of water adsorbed, etc.).
Then the impact of water in the establishment of adhesion will be particularly studied in relation to the mechanisms established for silicon and its oxide. The stress corrosion sensitivity of InP and GaAs surface oxides will be evaluated. Infrared spectroscopy and X-ray reflectivity studies at the synchrotron will support the conclusions.
A final axis will concern the mechanical properties of these materials to better understand their integration within heterostructures. Their ductile-brittle transition will be characterized using bonding on silicon or other substrates (silica, sapphire, etc.).
The candidate will be trained in all clean room technological tools allowing direct bonding (chemical cleaning, CMP polishing, bonding, thermal annealing) and their characterization (infrared spectroscopy, acoustic microscopy, anhydrous bonding energy measurement, X-ray reflectivity, mass spectrometry, etc.).
Towards sustainable electronics: impact and understanding of the substitution of high GWP gases on plasma etching processes
To address environmental concerns in the microelectronics industry, CEA-LETI is committed to an eco-innovation approach . In this context, the development of eco-responsible processes that reduce PerFluoro-Carbon (PFC) emissions is crucial . Plasma etching processes are a major emitter of PFCs because they traditionally use high GWP gases. The aim of this thesis will be to develop plasma etching processes on 300mm substrates by replacing fluorinated gases such as NF3, SF6 and CF4 with high GWP by F2 (GWP ~0). This work will involve understanding the changes induced in the etching processes for advanced devices. The dual challenge is to reduce the environmental impact while guaranteeing the high performance of these devices.
To achieve this objective, you will implement new F2-based mixtures on targeted applications for etching materials and cleaning reactors. You will provide comparative data on the performance of these new processes compared with reference processes in terms of etching results and the level of abatement of reaction by-products.
You will be based at the CEA-LETI Etching Laboratory. The work, which will be predominantly experimental on CEA-Leti's 300mm platform (see : https://www.youtube.com/watch?v=on1NH08AZfE), will benefit from the state-of-the-art process equipment and characterisation resources of the Nanotechnologies platform. The scientific and industrial interest of the subject guarantees that your work will be showcased in international communications. If you want your research to have an impact on society, apply now!
AI for SEM metrology: image generation and 3D reconstruction applied to microelectronic devices
Scanning Electron Microscopy (SEM) imaging is the current reference method for quality control in the microelectronic industry, due to the size of the objects involved and to the yield expected when these tools are used in production lines. In order to improve our knowledge on physics in play during imaging and to develop more performant post-processing software, synthetic images are necessary, representative of real images obtained in clean room conditions. Various state-of-the-art models are available to produce such images (by Monte-Carlo or mathematical approaches) but they are limited by their medium runtime performances or their lack of some typical imaging artifact. Such models are available in our laboratory and can be used during the PhD. Another solution deployed in other fields to rapidly produce images with realistic features is the image generation by deep learning neural network.
The goal of this thesis is to develop one or multiple deep learning models able to produce realistic SEM images from a chip design. Model hyperparameters as well as input dataset will be optimized to obtain images as close as possible to reality, according to metrics to define. This model will then be used to infer the chip design from the SEM image and/or reconstruct the 3D topography of the sample based on a top-down image. This thesis address the following question: to which extent a deep learning model is able to extract advanced metrology information from a SEM image, and what are the associated optimal conditions?
The Computational Patterning laboratory host this thesis. It is specialized in numerical methods to optimize manufacturing processes in clean room. The supervisor team from CEA is specialized in lithography process and numerical modelling, and is associated with Gipsa Lab for their expertise in neural network. This work is a follow-up of proof of concept developed since 2018 in the lab. The thesis contract is a fixed-term contract of 3 years, with a gross salary of 2043.54€ the first two years and 2104.62€ the final year. The PhD student will take part in scientific publications and international conferences. Competences developed during the PhD will be valuable for future positions in diverse technological domains, in particular in the current context of expansion of artificial intelligence.