1.
P Jäger; V Mertens; U Baumann; T Dullweber
In: IEEE Journal of Photovoltaics, Bd. 11, Nr. 1, S. 50-57, 2021.
@article{Jäger2020c,
title = {A Detailed Chemical Model for the Diffusion of Phosphorus Into the Silicon Wafer During POCl3 Diffusion},
author = {P Jäger and V Mertens and U Baumann and T Dullweber},
doi = {10.1109/JPHOTOV.2020.3038331},
year = {2021},
date = {2021-01-01},
journal = {IEEE Journal of Photovoltaics},
volume = {11},
number = {1},
pages = {50-57},
abstract = {The POCl 3 diffusion is the main technology to form the p-n junction of industrial silicon solar cells. However, the diffusion mechanism of phosphorus (P) into the silicon wafer is not fully understood. In this article, we study the P diffusion mechanism during drive-in by systematically varying the drive-in time in the oxygen (O 2 ) atmosphere and subsequently in nitrogen (N 2 ). When increasing the drive-in time in O 2 from 0 to 120 min, the sheet resistance R sheet stays constant at 485±30 Ω/sq. Hence, we demonstrate for the first time that the phosphorus diffusion can be completely suppressed in the O 2 atmosphere. When adding a drive-in in the N 2 atmosphere directly after the drive-in in O 2 , we find that the SiO 2 thickness d SiO2,O2 changes from initially 2 to 10 nm after O 2 drive-in to an equilibrium SiO 2 thickness d SiO2,eq of 4.7 nm after N 2 drive-in. We prove for the first time that if d SiO2,O2 > d SiO2,eq , no P diffuses into the silicon wafer even in the N 2 atmosphere. Only if d SiO2,O2 < d SiO2,eq , phosphorus diffuses into the silicon wafer in the N 2 atmosphere. We propose a detailed chemical model to explain our experimental results, which assumes that the diffusion of Si from the wafer through the SiO 2 interface toward the PSG plays a key role. In this model, P can only diffuse into the Si wafer if P 2 O 5 in the PSG is reduced by the Si from the wafer to P and SiO 2 .},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The POCl 3 diffusion is the main technology to form the p-n junction of industrial silicon solar cells. However, the diffusion mechanism of phosphorus (P) into the silicon wafer is not fully understood. In this article, we study the P diffusion mechanism during drive-in by systematically varying the drive-in time in the oxygen (O 2 ) atmosphere and subsequently in nitrogen (N 2 ). When increasing the drive-in time in O 2 from 0 to 120 min, the sheet resistance R sheet stays constant at 485±30 Ω/sq. Hence, we demonstrate for the first time that the phosphorus diffusion can be completely suppressed in the O 2 atmosphere. When adding a drive-in in the N 2 atmosphere directly after the drive-in in O 2 , we find that the SiO 2 thickness d SiO2,O2 changes from initially 2 to 10 nm after O 2 drive-in to an equilibrium SiO 2 thickness d SiO2,eq of 4.7 nm after N 2 drive-in. We prove for the first time that if d SiO2,O2 > d SiO2,eq , no P diffuses into the silicon wafer even in the N 2 atmosphere. Only if d SiO2,O2 < d SiO2,eq , phosphorus diffuses into the silicon wafer in the N 2 atmosphere. We propose a detailed chemical model to explain our experimental results, which assumes that the diffusion of Si from the wafer through the SiO 2 interface toward the PSG plays a key role. In this model, P can only diffuse into the Si wafer if P 2 O 5 in the PSG is reduced by the Si from the wafer to P and SiO 2 .
2.
P Jäger; V Mertens; U Baumann; T Dullweber
An Advanced Chemical Model for the Phosphorus Diffusion During Emitter Formation of Industrial Silicon Solar Cells Proceedings Article
In: WIP, (Hrsg.): Proceedings of the 37th European Photovoltaic Solar Energy Conference and Exhibition, S. 208-213, Online Event, 2020.
@inproceedings{Jäger2020b,
title = {An Advanced Chemical Model for the Phosphorus Diffusion During Emitter Formation of Industrial Silicon Solar Cells},
author = {P Jäger and V Mertens and U Baumann and T Dullweber},
editor = {WIP},
doi = {10.4229/EUPVSEC20202020-2BO.2.6},
year = {2020},
date = {2020-10-28},
booktitle = {Proceedings of the 37th European Photovoltaic Solar Energy Conference and Exhibition},
pages = {208-213},
address = {Online Event},
abstract = {The POCl3 diffusion is the main technology to form a pn-junction in todays industrial silicon solar cells. Despite decades of research, the mechanism for the diffusion of phosphorus (P) into the silicon wafer is still not fully understood in particular for the so-called in-situ oxidation during drive-in and will be investigated in this paper. We systematically vary the drive-in times in O2 as well as the subsequent drive-in times in N2. During drive-in in O2, the emitter sheet resistance stays constant, showing that it is possible to completely suppress the diffusion of P into the Si wafer in O2 atmosphere. The thickness of the SiO2 layer dSiO2,O2 increases from 2 to 10 nm with longer drive-in time in O2. During subsequent drive-in in N2, the SiO2 thickness reaches an equilibrium thickness dSiO2,eq of around 5 nm. Only if dSiO2,O2 < dSiO2,eq, P diffuses into the wafer during drive-in in N2. If dSiO2,O2 > dSiO2,eq, no P diffuses into the wafer during drive-in in N2 proving that no O2 is needed to inhibit the P diffusion. Based on these new experimental results, we propose an advanced chemical model for the diffusion of phosphorus during drive-in, where the diffusion of Si from the wafer surface through the SiO2 layer to the PSG is the key mechanism for reducing P2O5 to SiO2 and “free” P thus enabling the diffusion of phosphorus into the Si wafer. If the Si is oxidized by O2 or if the Si diffusion is blocked by a too thick SiO2 interlayer, the phosphorus remains an P2O5 in the PSG and hence cannot diffuse into the Si wafer.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The POCl3 diffusion is the main technology to form a pn-junction in todays industrial silicon solar cells. Despite decades of research, the mechanism for the diffusion of phosphorus (P) into the silicon wafer is still not fully understood in particular for the so-called in-situ oxidation during drive-in and will be investigated in this paper. We systematically vary the drive-in times in O2 as well as the subsequent drive-in times in N2. During drive-in in O2, the emitter sheet resistance stays constant, showing that it is possible to completely suppress the diffusion of P into the Si wafer in O2 atmosphere. The thickness of the SiO2 layer dSiO2,O2 increases from 2 to 10 nm with longer drive-in time in O2. During subsequent drive-in in N2, the SiO2 thickness reaches an equilibrium thickness dSiO2,eq of around 5 nm. Only if dSiO2,O2 < dSiO2,eq, P diffuses into the wafer during drive-in in N2. If dSiO2,O2 > dSiO2,eq, no P diffuses into the wafer during drive-in in N2 proving that no O2 is needed to inhibit the P diffusion. Based on these new experimental results, we propose an advanced chemical model for the diffusion of phosphorus during drive-in, where the diffusion of Si from the wafer surface through the SiO2 layer to the PSG is the key mechanism for reducing P2O5 to SiO2 and “free” P thus enabling the diffusion of phosphorus into the Si wafer. If the Si is oxidized by O2 or if the Si diffusion is blocked by a too thick SiO2 interlayer, the phosphorus remains an P2O5 in the PSG and hence cannot diffuse into the Si wafer.