Reliability of the copper (Cu) direct bonding interconnects for 3D integration
Copper direct bonding is one of the most promising approaches for 3-D integration. The process is mature as shown in the literrature for wafer to wafer (W2W) approach [1-3] but also in the case of a die to wafer one (D2W). However, its reliability is yet to be demonstrated even if the initial results from the PhD thesis of R. Taibi seem to be promising [4].
The purpose of this post-doc position will be first, to consolidate the results obtained by R. Taibi with the W2W approach and secondly, to study the reliability of the D2W approach from the electromigration and stress-induced voiding point of view.
The candidate will be responsible for all the reliability study, starting with the tests and the results’ analysis, failure analysis (optical, IR, SEM, FIB...), the determination of the degradation’s mechanisms.
1. Gueguen, P., et al. Copper direct bonding for 3D integration. in Interconnect Technology Conference, 2008. IITC 2008. International. 2008.
2. Taibi, R., et al. Full characterization of Cu/Cu direct bonding for 3D integration. in Electronic Components and Technology Conference (ECTC), 2010 Proceedings 60th. 2010.
3. Di Cioccio, L., et al., An Overview of Patterned Metal/Dielectric Surface Bonding: Mechanism, Alignment and Characterization. Journal of The Electrochemical Society, 2011. 158(6): p. 81-86.
4. Taibi, R., et al., Investigation of Stress Induced Voiding and Electromigration Phenomena on Direct Copper Bonding Interconnects for 3D Integration, in 2011 IEEE International Electron Devices Meeting (IEDM). 2011: Washington, DC.
Electrical Study of Conductive Bridge Random access Memory (CBRAM)
CBRAM memories are among the most promising technologies as alternative to Flash technologies which face strong problems of scaling. CBRAM have a capacitor-like stack, where a chalcogenide material is sandwiched between a silver anode and an inert cathode. Biasing the cell, silver ions diffuse in the chalcogenide matrix and reach the cathode where they reduce. A conductive bridge is formed between the electrodes causing a drop of resistance. Reversing the bias yields to a back-migration of silver, interrupting the conductive bridge. This kind of device can be operated at very low voltage (below 1 V) and can lead to extremely low power consumption.
The main objective of this postdoc position will be the electrical characterization aiming to a better comprehension of the physics involved in the device, with the final goal of a strong improvement in device characteristics, in particular concerning data retention. For this aim, in-depth characterization on particular features (i.e. conduction mode, failure mechanisms) will be performed, as much as possible linked to a first level of physical modelling linking current conduction and diffused ions in the matrix. The candidate will address both hardware & methodology issues, and particular attention will be devoted to pulsed measurements. Various process, geometries and architectures will be studied. A strong interaction with the specialists of materials characterizations (nano-characterization platform) will be promoted for a better physical knowledge of the structures.
Model reduction in dynamics : application to earthquake engineering problems
The complexity and refinement of the numerical models used to predict the behavior of structures under seismic loading often impose computation times of several days for solving the partial differential equations of the reference problem.
Furthermore, in the context of optimization , model identification, or parametric and stochastic analyses, the aim is not to predict the response of a unique model but of a family of models.
To reduce the computation time, model reduction techniques (Proper Orthogonal/Generalized Decomposition) may be considered. This post-doctoral study proposes to define and implement (especially in the FE code CAST3M) a technique suitable for the reduction of reinforced concrete type models subjected to seismic loading.
Droplets motion through modulation of surface energy gradient
Droplet motion through electro-wetting is nowadays largely studied and used in several systems and applications. In order to be useful, this technique needs an electrical field to monitor the droplet. For this post-doctoral fellowship, the main objective is to define an alternative method to the using of the electro-wetting technique in order to generate a droplet motion. The elaboration of surfaces with energy gradients conceived by thin film deposition or by laser ablation will be realized inside this study. The main difficulty is related to the patterns realization in order to obtain the appropriate hydrophilic/hydrophobic resolution. Apart from these “classical” techniques, an innovative method will be studied here by using switchable molecules. These molecules could modify the contact angle between a surface and a droplet, when acting on the potential of hydrogen (pH) or the wall temperature. For all the defined surfaces, the post-doctoral fellow will also analyze the coupling effect between the surface energy gradient and a thermal energy gradient on the droplet motion dynamics.
Study of aerosol transport through degraded materials
Radioactive Waste (RW) are produced during nuclear activities and are categorized as a function of their activities and their half-life in order to manage their conditioning, transport, storage… Mortar can be used in order to immobilize and/or create a safe barrier forming a Radioactive Waste Package (RWP) in order to protect the environment. It is important to study the efficiency of this mortar barrier for long term and safety assessment have to investigate the case of crack mortar formation as radioactive particles could then migrate in the cracks.
The LECD laboratory investigated this problematic by measuring the migration of CeO2 particle in mortar cracks using X-Ray microtomography. The cracks were synthesized by dissolving plastic molds (designed by 3D printing). This study showed the influence of particle interactions with tortuosity and roughness of the crack, but was limited to 40 µm particle diameter.
The aim of the postdoctoral work is to develop an experimental approach similar to the method developed to study the efficiency of HEPA filters, with particles of 0.05 - 5 µm diameter. Quantitative measurements will be performed on the particle flows on both sides of the cracked mortar sample. LECD has acquired an aerosol generator, a light-scattering aerosol spectrometer system for particle size analysis and concentration determination and an Universal Scanning Mobility Particle Sizers. The researcher will also develop modelling work using numerical tools as STARCCM+.
This project will be carried out under the format of an 12-month fixed-term contract at the Atomic Energy and Alternative Energies Commission (CEA), at the Cadarache site (Saint-Paul-lez-Durance, 13) at the Expertise and Destructive Characterization Laboratory (LECD) of the Expertise and Characterization CHICADE Service (SECC).
Contacts: ingmar.pointeau@cea.fr (R&D engineer) – Olivier.vigneau@cea.fr (Head of the Laboratory)
Porous layer integration for advanced temporary substrates
Double transfer of thin single crystalline processed layer can be very interesting for all technologies that require front and back side engineering of the silicon active film. With the increase of the electronical system complexity, this alternative technology can offer new opportunities to miniaturize the semiconductor devices. To fulfill such requirements, a recent alternative technology was developed at the CEA-LETI, based on the use of porous silicon substrates [1]. This new technology will be of a great interest for 3D integration, back-side imager but also MEMS or photovoltaics applications. This technology should now be validated at a larger scale, and we need to focus on all involved mechanisms such as the porous silicon layer rupture.
In a first place, the applicant should comprehend the specification of porous materials in thin film configuration, including elaboration steps and distinctive properties of transferred porous layers. Subsequently he/she may need to interact with Leti’s technological experts to determine process improvements to be implemented to reach pre-established specifications of desired prototypes. In order to evaluate and recommend appropriate materials and equipments, he/she may need to extensively focus on the behaviour of porous material under specific stress conditions such as chemical, thermal or mechanical solicitations. The purpose is to ensure compliance to Smart Cut or Smart stacking technologies that involve amongst others processes molecular bonding technology.
Later, the effort should be focused on the development of a specific technology to induce the mechanical separation inside the buried porous silicon layer. One line of approach would be to trigger the mechanical separation by ultrasound solicitation. Understanding the mechanisms of the splitting and characterising the resulting structures are part of the expected work to be completed in this project.
[1] A-S.Stragier et al., JECS,158 (5) H595-H599 (2011)
Unsupervised Few-Shot Detection of Signal Anomalies
Our laboratory, located at Digiteo in CEA Saclay, is looking for a postdoc candidate working on the subject of anomaly detection in manufacturing processes, for a duration of 18 months starting from Feburary 2022. This postdoc is part of HIASCI (Hybridation des IA et de la Simulation pour le Contrôle Industriel), a CEA LIST project in an internal collaboration which aims at building a platform of AI methods and tools for manufacturing applications, ranging from quality control to process monitoring. Our laboratory contributes to HIASCI by developping efficient methods of anomaly detection in acoustic or vibrational signals, operating with small amounts of training data. In this context, the detection of signal anomalies (DSA) consists of extracting from data the information about the physical process of manufacturing, which is in general too complex to be fully understood. Moreover, real data of abnormal states are relatively scarce and often expensive to collect. For these reasons we privilege a data-driven approach under the framework of Few-Shot Learning (FSL).
Design of a high-energy phase contrast radiography chain
As part of hydrodynamic experiments carried out at CEA-DAM, the laboratory is seeking, using pulsed X-ray imaging, to radiograph thick objects (several tens of mm), made of low-density materials (around 1 g/cm3), inside which shock waves propagate at very high speeds (several thousand m/s). For this type of application, it is necessary to use energetic X-ray sources (beyond 100 keV). Conventional X-ray imaging, which provides contrast due to variations in absorption cross sections, proves insufficient to capture the small density variations expected during the passage of the shock wave. A theoretical study recently carried out in the laboratory showed that the complementary exploitation of the information contained in the X-ray phase should enable better detectability. The aim of the post-doctorate is to provide experimental proof of concept for this theoretical study. For greater ease of implementation, the work will mainly focus on the dimensioning of a static X-ray chain, where the target is stationary and the source emits continuous X-ray radiation. Firstly, the candidate will have to characterize in detail the spectrum of the selected X-ray source as well as the response of the associated detector. In a second step, he (she) will design and have manufactured interference gratings adapted to high-energy phase measurements, as well as a representative model of the future moving objects to be characterized. Finally, the student will carry out radiographic measurements and compare them with predictive simulations. The student should have a good knowledge of radiation-matter interaction and/or physical and geometric optics. Proficiency in object-oriented programming and/or the Python and C++ languages would be a plus.
Lensfree Cytometry for High-troughput biological analysis
The new lensfree imaging is against the foot of the recent developments in microscopy that focuses today on super-resolution achievements. Instead lensfree imaging offers several advantages: field of view (FOV) can cover several cm2, resolution in the range of 0.5µm to 3µm, mostly compact sizes and ease of use. The technique is based on holography online as invented by Gabor [1]. A biological object is illuminated by a coherent light, micrometric structures of the object diffract and the light interferes with the incident wave. The amplitude of the interference is recorded by a CMOS sensor and the image is reconstructed thanks to inverse-problem approaches. Albeit the method exists since 1970, the recent development of large field, small pixel size digital sensors helped realize the full potential of this method only since 2010.
At CEA-LETI Health Division, a new microscopic platform based on this principle has been developed. Its applicability for performing high-throughput monitoring of major cell functions such as cell-substrate adhesion, cell spreading, cell division, cell division orientation, cell migration, cell differentiation, and cell death have been demonstrated [2,3]. The new project proposed in this PostDoc is dealing with the development of an innovative lensfree cytometry setup aiming at high-throughput analysis of biological samples, e.g. cell counting, cell sorting, etc. The post-doctoral fellow will develop the instrumentation and methods and will conduct the experimentation and analysis of true biological samples.