3D integration is a major and durable integration technology developed since the beginning of 21st century by all major semiconductor companies and several large research institutes for electronic, imaging and sensing miniaturized systems. It is based on the stacking and bonding of thinned silicon wafers/chips with electrical vias (vertical interconnect access) for die to die interconnections. This enables to benefit from a global size reduction, from a broad range of new functionalities offered by heterogeneous integration, and from new packaging capabilities with a high contact density. It will also reduce issues related to 2D integration and devices downscaling below the 14 nm node. One of the key technologies for 3D IC, 2,5D (with interposer) and 3D packaging integration processes is the fabrication of high aspect ratio vertical interconnections by Through Silicon Vias (TSV). This technology generates new challenging metrology needs that must be solved. The SME FOGALE nanotech is one the industrial leaders for the metrology of 3D integration processes and TSV, and many major semiconductor companies and foundries worldwide use or are acquiring their metrology solutions. Those solutions comply with current requirements but must be secured, improved and extended for future metrology needs predicted by the International Technology Roadmap for Semiconductors (ITRS). The OLOVIA project combines the expertise of FOGALE nanotech, IEF and IOGS in optical instrumentation, interferometry techniques and optical modelling to tackle this challenge. Thus, the general objective of OLOVIA project will be to introduce non destructive, quantitative, accurate, reliable and high throughput optical tools able to satisfy challenging metrology needs for in line control of TSV industrial fabrication processes. Those optical tools will address two main issues of TSV metrology: i) the measurement of etched via geometrical parameters (depth, top and bottom diameters, shape, sidewall roughness, remaining silicon thickness), and ii) the mapping of mechanical stress field generated around the vias at various stages of the fabrication process. Specifically, i) Via geometry measurements will be based on the design and implementation of new measurement procedures/versions of low coherence interferometry and advanced microscopy techniques existing at FOGALE nanotech and IEF ii) stress field measurements will rely on the development of a new full field microscopic photoelasticity system with fast phase modulation able to work both in the transmission and in the reflection modes. Both optical systems will be designed to be compatible with industrial use. They will be based on advanced finite element simulations of the light-beam interactions at the nanoscale in and around a via at IOGS, on in depth performance analysis of optical systems and associated phase demodulation techniques at IEF and FOGALE nanotech, and on extensive tests on dedicated samples fabricated at IEF. In addition, a photoelastic constant calibration system will be built and comparative measurements with reference techniques (cross sectional SEM/TEM, Raman spectroscopy,...) will be performed to ascertain the performances of the developed optical systems. Finally, the optical systems will be qualified on industrial samples with various TSV technologies. Finally, other potential applications in the semiconductor field such as defect inspection of wafer bonding processes, as well as local stress measurements on MEMS and wafer-level packages will be explored.

Single Crystal quartz is still currently the essential material for the development of high performance inertial MEMS sensors and time references, because of its piezoelectric properties and its good performance temperature stability. ONERA and RAKON, major actors in their respective domains, develop micro-sensors and time references aiming at the defence (navigation) and mobile phone markets. The operation principle of these structures is based on a mechanical resonator made of single quartz package in vacuum to improve its performances. Naturally, the performances of the packaged structures is highly dependent on the long term stability of the vacuum inside the package. These applicative markets are currently turning towards the 3D integration of small size structure (typically <1 cm3). To answer these new needs, ONERA and RAKON are in the urge of reducing the volume of their current solutions by working on the packaging technique. A reduction of 4 fold of the packaged volume is seeked. An important development has already been done on the packaging of silicon-based structures. The originality of the work proposed in this project is the following : - The used substrate is single quartz, which implies the development of low température processes (<300°C) in ordre to preserve the piezoelectric properties of the material and the quality of the metallic contacts (important for piezo actuation and détection). - The package volume and the base pressure (10-3 mbar) imply a very low leak rate compared to the state of the art (about 10-15 atm.cm3/s) in order to maintain the vacuum level during several years. - Therefore, adapted measurement techniques need to be set up to allow such a measurement Finally, getter materials associating low température activation (<300 °C) and high performance need to be developed and packaged. FOGALE NANOTECH has been developing for 10 years measurement solutions dedicated to the characterization of micro-resonators. Emanating from several industrial partners, the urging demand for control setups dedicated to the characterization of packaged structures motivâtes FOGALE to take place in this collaborative project. In this project, we propose to develop packaging processes compatible with the intégration of high performance, quartz based MEMS resonators (ONERA) and BAW time references (RAKON), with the following performances : low température (<300 °C), low residual pressure (<10-3 mbar), low leak rate (<10E-16 atm.cm3/s). In order to ensure the industrial transfer of the packaging processes developed in this project, a part of these processes will be transferred to RAKON in the framework of this project. Moreover, the characterization means set up by FOGALE will give rise to a commercial product dediacted to control lines. The consortium ONERA / Université Paris Sud (IEF) / FOGALE / RAKON gathers four entities identified as major actors in their specific domain of expertise. The PRESTIGE project will gather all the necessary know-how, from realizations and material development on quartz material to the characterization techniques dans industrial transfer.