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Saw Damage as an Etch Mask for the Acidic Texturization of Multicrystalline Silicon Wafers

  • The surface of multicrystalline silicon solar cells are etched by mixtures of HF, HNO3 and H2SiF6 in order to remove saw damage caused by wafer slicing, as well as to create a water surface topography that provides a low reflectance for incident light, otherwise known as the texture. Topographically analyzing wafer surfaces before and after etching has revealed that the saw damage controls the texturized wafer surface’s final topography.The first key factor is the dimension and magnitude of the plastic stress field introduced by indenting SiC grains into the wafer surface during the wafering process. The second key factor is that lattice-stressed silicon is etched at a higher rate than unstressed bulk silicon. At the wire entrance, side sharp and large SiC grains create the deepest indention pits, and therefore the deepest of the water surface stress fields. The lattice-disturbed silicon inside these pits is etched at a higher rate compared to the pit’s side walls, which are uniformly attacked across the wafer area. Consequentially,The surface of multicrystalline silicon solar cells are etched by mixtures of HF, HNO3 and H2SiF6 in order to remove saw damage caused by wafer slicing, as well as to create a water surface topography that provides a low reflectance for incident light, otherwise known as the texture. Topographically analyzing wafer surfaces before and after etching has revealed that the saw damage controls the texturized wafer surface’s final topography.The first key factor is the dimension and magnitude of the plastic stress field introduced by indenting SiC grains into the wafer surface during the wafering process. The second key factor is that lattice-stressed silicon is etched at a higher rate than unstressed bulk silicon. At the wire entrance, side sharp and large SiC grains create the deepest indention pits, and therefore the deepest of the water surface stress fields. The lattice-disturbed silicon inside these pits is etched at a higher rate compared to the pit’s side walls, which are uniformly attacked across the wafer area. Consequentially, existing pits deepen, and these areas generate the wafer’s lowest reflectivity. At the wire exit side, a higher number of smaller and rounder SiC particles indent the surface and create more numerous and shallower indention pits compared to the wire entrance side. The resulting stress field is less deep, so less silicon is removed from inside of these pits during etching compared to the wire entrance side. This yields to a wafer surface region consisting of shallowly etched pits and higher reflectance. It is concluded that the saw damage acts like an etch mask in the texturization of multicrystalline silicon wafers.show moreshow less

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Metadaten
Author: Jörg AckerORCiDGND, Thomas LangnerORCiD, Birgit Meinel, Tim Sieber
URL:https://www.sciencedirect.com/science/article/pii/S1369800117313896
DOI:https://doi.org/10.1016/j.mssp.2017.09.039
ISSN:1369-8001
Title of the source (English):Materials Science in Semiconductor Processing
Document Type:Scientific journal article peer-reviewed
Language:English
Year of publication:2018
Tag:acidic etching; confocal microscopy; multi-wire sawing; silicon; solar cell; stress field; texturization
Volume/Year:74
First Page:238
Last Page:248
Faculty/Chair:Fakultät 2 Umwelt und Naturwissenschaften / FG Physikalische Chemie
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