Centre d’Élaboration de Matériaux et d’Etudes Structurales (UPR 8011)


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Modelling of point defect complex formation

par Evelyne Prevots - publié le , mis à jour le

The researchers from CEMES (CNRS), INAC and LETI (CEA) have proposed an original model describing the aggregation of point defects and impurities in the form of stable complexes in a crystal. This general model, following the point defect encounters and the energy gains, is validated via its ability to simulate the strains introduced in silicon by H+ ion implantation at room temperature.

The diffusion and interaction of impurity atoms in semiconductors play an important role and should be taken into account in modelling of the technological processes for semiconductor device fabrication. Being mobile, impurity atoms, vacancies and interstitials can recombine and/or precipitate in the form of stable complexes which leads to the modification of target material properties. The researchers from CEMES (CNRS), INAC and LETI (CEA) have proposed an analytic model that predicts the concentrations of such complexes as a function of point defect concentrations and of temperature. This model describes the aggregation of point defects and impurities using the probabilities for point defects to encounter and the probabilities for the formation of specific complexes. The latter depend on the complex formation energies that were calculated using the density functional theory. This approach is general and can be used whatever impurities or crystal are considered.

The researchers applied and validated this model being interested in the formation of different complexes after H+ implantation in silicon at room temperature. The macroscopic strain that can be measured in the implanted crystal was linked to the individual deformation fields generated by the different complexes. The model was validated and complex concentrations were derived from the comparison with the experimental results obtained by X-ray diffraction. Such model calibration allowed determining the diffusion coefficients of silicon vacancies and interstitials at room temperature, the time required for the formation of all the complexes, the concentrations of complexes as a function of H concentration and the specific role of some complexes in generating strain. The model can be applied for simulating then optimizing the Smart Cut® technology used for creating innovative substrates for microelectronics like SOI and its derivatives. These results were published in Acta Materialia.

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(a) Libres parcours des défauts A et B dans les référentiels fixe et mobile ; (b) Répartition de l’hydrogène et des défauts ponctuels dans les différents complexes en fonction de la concentration d’hydrogène implanté.
© CEMES-CNRS

 

Contact

Dr Nikolay Cherkashin : nikolay.cherkashin chez cemes.fr

 

Reference

N. Cherkashin, F.-X. Darras, P. Pochet, S. Reboh, N. Ratel-Ramond, A. Claverie, “Modelling of point defect complex formation and its application to H+ ion implanted silicon”, Acta Materialia 99 (2015) 187–195.

DOI : 10.1016/j.actamat.2015.07.078