Multiple pathways for permanent deactivation of boron-oxygen defects in p-type silicon

Nampalli, Nitin; Li, Hongzhao; Kim, Moonyong; Stefani, Bruno Vicari; Wenham, Stuart; Hallam, Brett; Abbott, Malcolm

doi:10.1016/j.solmat.2017.06.041

Cited by 27 publications

(19 citation statements)

References 31 publications

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“…These trends in degradation behaviour with firing temperature and cooling rate correlate well with the present study. In contrast to LeTID, an increase in peak firing temperature and cooling rate is known to decrease the magnitude of BO-LID, 33,34 which is opposite to the trend observed here. However, an increase in non-BO related LID has been observed in Cz silicon at peak firing temperatures above $650 C. 33,35 While such effects have been attributed to LeTID, 36,37 the possibility of Cu-LID being responsible for such LID effects has not been specifically precluded in such studies.…”

Section: à3contrasting

confidence: 99%

“…In contrast to LeTID, an increase in peak firing temperature and cooling rate is known to decrease the magnitude of BO-LID, 33,34 which is opposite to the trend observed here. However, an increase in non-BO related LID has been observed in Cz silicon at peak firing temperatures above $650 C. 33,35 While such effects have been attributed to LeTID, 36,37 the possibility of Cu-LID being responsible for such LID effects has not been specifically precluded in such studies. It must be noted that there exist other empirical differences between LeTID and Cu-LID (e.g., SRH properties 29,38,39 and activation energy of degradation 31,38 ).…”

Section: à3contrasting

confidence: 99%

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Rapid thermal anneal activates light induced degradation due to copper redistribution

Nampalli

Laine

Colwell

et al. 2018

Applied Physics Letters

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While it is well known that copper impurities can be relatively easily gettered from the silicon bulk to the phosphorus or boron–doped surface layers, it has remained unclear how thermally stable the gettering actually is. In this work, we show experimentally that a typical rapid thermal anneal (RTA, a few seconds at 800 °C) used commonly in the semiconductor and photovoltaic industries is sufficient to release a significant amount of Cu species from the phosphorus-doped layer to the wafer bulk. This is enough to activate the so-called copper-related light-induced degradation (Cu-LID) which results in significant minority carrier lifetime degradation. We also show that the occurrence of Cu-LID in the wafer bulk can be eliminated both by reducing the RTA peak temperature from 800 °C to 550 °C and by slowing the following cooling rate from 40–60 °C/s to 4 °C/min. The behavior is similar to what is reported for Light and Elevated Temperature degradation, indicating that the role of Cu cannot be ignored when studying other LID phenomena. Numeric simulations describing the phosphorus diffusion and the gettering process reproduce the experimental trends and elucidate the underlying physical mechanisms.

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Section: à3contrasting

confidence: 99%

Section: à3contrasting

confidence: 99%

Rapid thermal anneal activates light induced degradation due to copper redistribution

Nampalli

Laine

Colwell

et al. 2018

Applied Physics Letters

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“…It appears that the rapid cool down from the high temperature plays a critical role in determining the defect concentration [75,78], possibly through a reduction in [O i ] [79]. This influence is supported by recent studies, which have shown that the fast-firing process used for the metallisation of industrial silicon solar cells can lead to a permanent reduction in the B-O defect concentration [73,[80][81][82]. Extended anneals at lower temperatures in the range of 400-700 • C can also reduce the B-O defect concentration probably through a reduction in the concentration of interstitial oxygen dimers [78,79]; however, extended annealing at sub-optimal conditions can also lead to an increase in the B-O defect concentration [72].…”

Section: Thermal Processingmentioning

confidence: 83%

“…Thermal processing can reduce the extent of B-O related degradation by reducing the concentration of the B-O defect and precursors [72,73]. For example, high-temperature processes such as phosphorus diffusion, thermal oxidation and annealing can reduce the B-O defect concentration and therefore increase the stable excess carrier lifetime of the silicon [8,13,[74][75][76][77].…”

Section: Thermal Processingmentioning

confidence: 99%

Eliminating Light-Induced Degradation in Commercial p-Type Czochralski Silicon Solar Cells

et al. 2017

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This paper discusses developments in the mitigation of light-induced degradation caused by boron-oxygen defects in boron-doped Czochralski grown silicon. Particular attention is paid to the fabrication of industrial silicon solar cells with treatments for sensitive materials using illuminated annealing. It highlights the importance and desirability of using hydrogen-containing dielectric layers and a subsequent firing process to inject hydrogen throughout the bulk of the silicon solar cell and subsequent illuminated annealing processes for the formation of the boron-oxygen defects and simultaneously manipulate the charge states of hydrogen to enable defect passivation. For the photovoltaic industry with a current capacity of approximately 100 GW peak, the mitigation of boron-oxygen related light-induced degradation is a necessity to use cost-effective B-doped silicon while benefitting from the high-efficiency potential of new solar cell concepts.

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“…Furthermore, a dual role of the firing process has been recently identified with the thermal elimination of defect precursors, as well as modulating the hydrogen concentration in the silicon, which leads to a change in the rate of passivation. [107] A significant challenge for industrial boron-doped Czochralski silicon solar cells has been how to incorporate an effective illuminated annealing process into the production environment, with a throughput of 3600 wafers h À1 . Early work required minutes to hours for the complete elimination of B-Orelated degradation.…”

Section: Hydrogenation Of Carrier-induced Defectsmentioning

confidence: 99%

Overcoming the Challenges of Hydrogenation in Silicon Solar Cells

et al. 2018

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The challenges of passivating defects in silicon solar cells using hydrogen atoms are discussed. Atomic hydrogen is naturally incorporated into conventional silicon solar cells through the deposition of hydrogen-containing dielectric layers and the metallisation firing process. The firing process can readily passivate certain structural defects such as grain boundaries. However, the standard hydrogenation processes are ineffective at passivating numerous defects in silicon solar cells. This difficulty can be attributed to the atomic hydrogen naturally occupying low-mobility and low-reactivity charge states, or the thermal dissociation of hydrogen–defect complexes. The concentration of the highly mobile and reactive neutral-charge state of atomic hydrogen can be enhanced using excess carriers generated by light. Additional low-temperature hydrogenation processes implemented after the conventional fast-firing hydrogenation process are shown to improve the passivation of difficult structural defects. For process-induced defects, careful attention must be paid to the process sequence to ensure that a hydrogenation process is included after the defects are introduced into the device. Defects such as oxygen precipitates that form during high-temperature diffusion and oxidation processes can be passivated during the subsequent dielectric deposition and high-temperature firing process. However, for laser-based processes performed after firing, an additional hydrogenation process should be included after the introduction of the defects. Carrier-induced defects are even more challenging to passivate, and advanced hydrogenation methods incorporating minority carrier injection must be used to induce defect formation first, and, second, provide charge state manipulation to enable passivation. Doing so can increase the performance of industrial p-type Czochralski solar cells by 1.1 % absolute when using a new commercially available laser-based advanced hydrogenation tool.

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Multiple pathways for permanent deactivation of boron-oxygen defects in p-type silicon

Cited by 27 publications

References 31 publications

Rapid thermal anneal activates light induced degradation due to copper redistribution

Rapid thermal anneal activates light induced degradation due to copper redistribution

Eliminating Light-Induced Degradation in Commercial p-Type Czochralski Silicon Solar Cells

Overcoming the Challenges of Hydrogenation in Silicon Solar Cells

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