Porosity evaluation of PoSi wafer using a nondestructive ultrasonic technic
Résumé
The manufacturing processes of porous silicon (PoSi) by electrochemical etching now allow samples with variable depths and variable degrees of porosity to be obtained. However, thickness and porosity measurement methods of PoSi are generally destructive. Therefore in this study a nondestructive ultrasonic method is investigated. For this, an immersion insertion-substitution technique has been used. Samples with different porosities and depths are studied. The thickness of the wafer (550 microns) and high sound speed in pure silicon (8450 m.s-1) require transducers with high central frequencies (from 15 to 50MHz). The acoustic parameters of the wafer, such as velocity and attenuation are measured. These measurements are compared with those obtained through a one-dimensional multilayer model of the wafer, using a homogenisation approach for the porous layer. An inverse method is used to find the PoSi parameters, such as the thickness of the layers or the porosity.
Domaines
Acoustique [physics.class-ph]
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