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Advanced X-ray characterization for the development of low consumption power transistors

Abstract : CEA-Leti develops power electronics components with high energy efficiency, based on semiconductors of the III-N group (GaN, AlGaN, InGaN…), in particular in partnership with ST microelectronics. In order to minimize the costs and improve the compatibility with the standards of microelectronics industry, CEA-Leti chose to produce epitaxial thin films of GaN grown on silicon substrates. However, these two materials have large mismatches of coefficient of thermal expansion and lattice parameter. The resulting GaN layers are affected by strong gradients of mechanical stress and dislocation density throughout their thickness. As component performances and wafer fragility are linked to crystalline quality and stress state of these thin films, it is important to have access to effective, rapid and non-destructive metrology tools. To this end, this PhD focuses on the study of GaN layers by X-ray diffraction (XRD), which is an acknowledged and widely used technique for the analysis of epitaxial films. The effect of stress gradient on XRD measurements is an asymmetrical broadening of diffraction peaks. We suggest extracting this gradient by reproducing the experimental XRD signal, by means of a simulation of the diffracted intensity stemming from a distorted crystal. A good agreement between simulations and measurements is obtained when modelling local variations of the strain profile throughout the surface plane. For the quantification of dislocations extending through the thickness of GaN layers, we suggest a simple methodology, based on the measurement of the micro-strain field surrounding the dislocations. The study shows how to use this type of measurement on GaN layers with strong stress gradient. In addition, the results are compared to the dislocation densities obtained with alternative characterization techniques such as transmission electron microscopy, cathodoluminescence or XRD, via an analysis of crystal lattice misorientations. The studies of stress gradient and dislocation density, initially carried out on complete stacks of III-N layers, are enlighten by means of in-depth measurements on progressively etched films of GaN.
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https://tel.archives-ouvertes.fr/tel-03404254
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Submitted on : Tuesday, October 26, 2021 - 3:19:10 PM
Last modification on : Wednesday, October 27, 2021 - 3:36:05 AM

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  • HAL Id : tel-03404254, version 1

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STAR | CEA | DRT | LETI | CEA-GRE

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Victor Yon. Advanced X-ray characterization for the development of low consumption power transistors. Materials Science [cond-mat.mtrl-sci]. Université Grenoble Alpes [2020-..], 2021. English. ⟨NNT : 2021GRALY009⟩. ⟨tel-03404254⟩

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