Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al2O3 Capping Layers

Guangtao Yang,Gianluca Limodio,Arthur Weeber,Jimmy Melskens,Maciej Stodolny,Bas Van De Loo,W M M Kessels,Olindo Isabella,Miro Zeman,Bart Macco,Paula Bronsveld

doi:10.1109/jphotov.2021.3119595

Abstract

Hydrogenation of polycrystalline silicon (poly-Si) passivating contacts is crucial for maximizing their passivation performance. This work presents the application of Al 2 O 3 prepared by atomic layer deposition as a hydrogenating capping layer. Several important questions related to this application of Al 2 O 3 are addressed by comparing results from Al 2 O 3 single layers, SiN <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x single layers, and Al 2 O 3 /SiN <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x double layers to different poly-Si types. We investigate the effect of the Al 2 O 3 thickness, the poly-Si thickness, the poly-Si doping type, and the postdeposition annealing treatment on the passivation quality of poly-Si passivating contacts. Especially, the Al 2 O 3 /SiN <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x stack greatly enhances the passivation quality of both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n + and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p + doped as well as intrinsic poly-Si layers. The Al 2 O 3 layer thickness is crucial for the single-layer approach, whereas the Al 2 O 3 /SiN <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x stack is less sensitive to the thickness of the Al 2 O 3 layer. A thicker Al 2 O 3 layer is needed for effectively hydrogenating <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p+ compared to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n+ poly-Si passivating contact. The capping layers can hydrogenate poly-Si layers with thicknesses up to at least 600 nm. The hydrogenation-enhanced passivation for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n + poly-Si is found to be more thermally stable in comparison to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p + poly-Si. These results provide guidelines on the use of Al 2 O 3 capping layers for poly-Si contacts to significantly improve their passivation performance.

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