Invited Lecture
W and Fe redistribution in Si during annealing and oxidation

Low concentrations of metallic impurities in silicon (Si) substrates can lead to significant device electronic property degradations, decreasing device production yield. Due to microelectronic device size reductions, the current tolerable contamination concentration levels are particularly low (~ 10¹⁰ cm^-2). These very low levels cannot be detected with conventional surface analysis techniques such as Auger electron spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy, and are also too low to be detected with usual bulk analysis tools such as secondary ion mass spectrometry, complicating device failure interpretations. It is thus necessary to identify contaminant possible effects on fabrication processes, and to be able to simulate contamination redistribution at levels lower than detection limits during device fabrication, in order to potentially identify their influence on device electrical properties [1-3].

In this work, the redistributions of tungsten (W) and iron (Fe) atoms in Si are studied during thermal annealing and during Si thermal oxidation. In a first part, a detailed study of W diffusion is presented, showing that W probably uses an original diffusion mechanism, involving interstitial W-self-interstitial pair diffusion [4]. In the second part, the mechanisms involved with Fe redistribution at the mobile SiO₂/Si interface during Si oxidation are presented, allowing Si pyramidal defect formation at this interface [5] to be understood [6].

[1] Boucard et al., Mat. Sci. Eng. B 124-125 (2005) 409

[2] Pfäffli et al., Microelec. Reliability 52 (2012) 1761

[3] Mekheldi et al., Results in Physics 6 (2016) 80

[4] De Luca et al., J. Appl. Phys. 115 (2014) 013501

[5] Wong-Leung et al., J. Appl. Phys. 83 (1998) 580

[6] De Luca et al., J. Appl. Phys. 117 (2015) 115302