Analyse Expérimentale et Numérique des Contraintes Thermomécaniques Induites lors des Procédés Émergents de Fabrication de Puces Électroniques au moyen des Capteurs Embarqués

Abstract : For the thermomechanical stress assessment in silicon, piezoresistive sensors (in rosette) composed of 4nMOS and 4pMOS were developed and embedded into microelectronic products.The characteristic relations between piezoresistive, electrical and mechanical quantities were established.Piezoresistive quantities were identified thanks to a four-points bending calibration machine. This machine was designed and fabricated in the frame of this PhD and enables applying a known uniform uniaxial stress into silicon sample and then calculating the three piezoresistive coefficients.The sensors embedded into different technologies such as CMOS65, BiCMOS55, CMOS40, BSI140 and PIC25 were calibrated with this machine.These MOS sensors were used for studying stresses induced by TSV (CMOS65 technology), by packaging with 3D stacking (CMOS65 technology) and 2D stacking (BiCMOS55 technology).The results give stress components (σyy, σzz) which are not in a good agreement with simulation results. Electrical responses of the MOS oriented at 90° ([010] direction with respect to the x axis ([100] direction)) are questioned because the coefficients (π12) obtained from this MOS acts directly on the two components.In addition, stress variations in sensors area, as well as inter-chips and inter-wafers variabilities disturb the results.Integrated into the same test chip of the CMOS40 technology, different structures were studied, namely the MOS transistors, the bandgap structure and the poly-Si resistances which were also calibrated.For this technology, a study of thermomechanical stress induced by packaging revealed a significant impact on the output responses (MOS mobility, bandgap voltage). Through a minimization parametric study, this impact was reduced by controlling the geometrical dimensions of components and the material properties of the moulding compound.These results show that, MOS rosettes can be used as stress sensors but with a limited efficiency. The use of active resistances as stress sensors is therefore envisaged. However, these MOS can be used to study the impact of stresses on the chip operation.
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Komi Atchou Ewuame. Analyse Expérimentale et Numérique des Contraintes Thermomécaniques Induites lors des Procédés Émergents de Fabrication de Puces Électroniques au moyen des Capteurs Embarqués. Matériaux. PSL Research University, 2016. Français. ⟨NNT : 2016PSLEM006⟩. ⟨tel-01405347⟩

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