Multi-Isotopic Analysis for Robust Traceability of Crystalline Silicon Wafers

This work investigates tracking methods to authenticate the origin of crystalline silicon (c-Si) wafers used by the PV industry and to identify those from companies using forced labor during fabrication. Along these lines, the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">29</sup>Si/<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup>Si and the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sup>Si/<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup>Si isotopic ratios (δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">29</sup>Si and δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sup>Si, resp.) in c-Si wafers sourced from seven different suppliers worldwide were analyzed using highly sensitive and highly precise atomic mass spectrometry techniques, namely multi-collector inductively coupled plasma mass spectroscopy (MC-ICPMS) and femtosecond laser ablation ICPMS. The analysis of the sourced cSi wafers revealed a clear, unique (δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sup>Si, δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">29</sup>Si) isotopic footprint for each manufacturer, with δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sup>Si (resp. δ<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">29</sup>Si) spanning between ±1.50 ‰ (resp. ±1.00 ‰) and excellent R<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> values. Even if the root causes of the isotopic fractionation along the c-Si wafer production stream are still to be evidenced, these results open the way to a robust and unambiguous method to authenticate c-Si wafers. Applications and replications to other c-Si-based devices are foreseen, such as for chips and detectors, where the requests for supply chain transparency and traceability exist as well.