Impurity gettering effect of atomic layer deposited aluminium oxide films on silicon wafers

Liu, AnYao; Macdonald, Daniel

doi:10.1063/1.4983380

Cited by 25 publications

(40 citation statements)

References 18 publications

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“…Hence, hydrogen can mainly diffuse in the wafer only from the rear side through the CVD AlO x film, resulting in weaker LeTID. Alternatively, the charge polarity in the thin film may have an effect, since both plasma‐enhanced CVD SiN x and ALD AlO x are known to getter metal impurities . Nevertheless, the largest degradation is observed in the non‐textured edges of the SiN x ‐passivated b‐Si cells, which is an interesting finding and will be discussed later in more detail.…”

Section: Resultssupporting

confidence: 80%

“…Additionally, gettering may be intensified also by accumulation of impurities at the AlO x –Si interface or into the SiN x bulk during post‐deposition heat treatments . This may have a stronger effect in b‐Si, since the large surface area of the nanostructure provides more gettering sites at the dielectric‐Si interface.…”

Section: Resultsmentioning

confidence: 99%

“…Alternatively, the charge polarity in the thin film may have an effect, since both plasma-enhanced CVD SiN x and ALD AlO x are known to getter metal impurities. 35,36 Nevertheless, the largest degradation is observed in the non-textured edges of the SiN x -passivated b-Si cells, which is an interesting finding and will be discussed later in more detail. Finally, Figure 3C reveals that the degradation is rather uniform laterally in good grain areas, which is characteristic of LeTID.…”

mentioning

confidence: 78%

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Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

Pasanen

Modanese

Vähänissi

et al. 2018

Progress in Photovoltaics

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Light and elevated‐temperature induced degradation (LeTID) is currently a severe issue in passivated emitter and rear cells (PERC). In this work, we study the impact of surface texture, especially a black silicon (b‐Si) nanostructure, on LeTID in industrial p‐type mc‐Si PERC. Our results show that during standard LeTID conditions the b‐Si cells with atomic‐layer‐deposited aluminum oxide (AlOx) front surface passivation show no degradation despite the presence of a hydrogen‐rich AlOx/SiNx passivation stack on the rear. Furthermore, b‐Si solar cells passivated with silicon nitride (SiNx) on the front lose only 1.5%rel of their initial power conversion efficiency, while the acidic‐textured equivalents degrade by nearly 4%rel under the same conditions. Correspondingly, clear degradation is visible in the internal quantum efficiency (IQE) of the acidic‐textured cells, especially in the ~850 to 1100‐nm wavelength range confirming that the degradation occurs in the bulk, while the IQE remains nearly unaffected in the b‐Si cells. The observations are supported by spatially resolved photoluminescence (PL) maps, which show a clear contrast in the degradation behavior of b‐Si and acidic‐textured cells, especially in the case of SiNx front surface passivation. The PL maps also suggest that the magnitude of LeTID scales with surface area of the texture, rather than wafer thickness that was recently reported, although the b‐Si cells are slightly thinner (140 vs 165 μm). The results indicate that b‐Si has a positive impact on LeTID, and hence, benefits provided by b‐Si are not limited only to the excellent optical properties, as commonly understood.

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 78%

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Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

Pasanen

Modanese

Vähänissi

et al. 2018

Progress in Photovoltaics

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“…Following a steep decrease, the concentration peaks around the SiN x /Si interface corresponded to the metals gettered to the interface. The mechanism of aggregation of the metals at the interface is not fully understood at this stage, but is likely a segregation gettering mechanism . The result that the metals were gettered to the interface is consistent with what was observed on HP mc‐Si wafers in Ref.…”

supporting

confidence: 87%

Transition Metals in a Cast‐Monocrystalline Silicon Ingot Studied by Silicon Nitride Gettering

Sun

Liu

Samadi

et al. 2019

Physica Rapid Research Ltrs

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The concentrations of Cr, Fe, Ni, and Cu in a cast‐monocrystalline silicon ingot grown for solar cell applications are reported. Wafers taken from along the ingot are coated with silicon nitride films and annealed, causing mobile impurities to be gettered to the films. Secondary ion mass spectrometry is applied to measure the metal content in the silicon nitride films. The bulk concentrations of the gettered metals in samples along the ingot are found to be: Cr (3.3 × 1010–3.3 × 1011 cm−3), Fe (3.2 × 1011–2.5 × 1012 cm−3), Ni (1.5 × 1012–1.3 × 1013 cm−3), and Cu (7.1 × 1011–3.2 × 1013 cm−3). For each metal, the lower limit is measured on the wafer from the middle of the ingot, and the higher limit is measured on wafers from the bottom or the top. The results are compared with similar data recently measured on a high‐performance multicrystalline silicon ingot. The results provide insights into the total bulk concentrations of the metals in cast‐grown ingots.

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“…Although not explicitly proven, it is often assumed that hydrogen enters the bulk from as‐deposited SiN x films or those annealed at low temperatures. Impurities can also be gettered to dielectrics or their interface with the silicon bulk . Temporary passivation is performed at room or low temperature so even if external gettering were possible (e.g., to a temporary thin film) kinetic limitations would mean effective external gettering were impossible for key impurities such as iron.…”

Section: Applications Of Temporary Passivation For Silicon Materials mentioning

confidence: 99%

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

Grant

Murphy

2017

Physica Rapid Research Ltrs

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Accurate measurements of the bulk minority carrier lifetime in high-quality silicon materials is challenging due to the influence of surface recombination. Conventional surface passivation processes such as thermal oxidation or dielectric deposition often modify the bulk lifetime significantly before measurement. Temporary surface passivation processes at room or very low temperatures enable a more accurate measurement of the true bulk lifetime, as they limit thermal reconfiguration of bulk defects and minimize bulk hydrogenation. In this article we review the state-of-the-art for temporary passivation schemes, including liquid immersion passivation based upon acids, halogen-alcohols and benzyl-alcohols, and thin film passivation usually based on organic substances. We highlight how exceptional surface passivation (surface recombination velocity below 1 cm s À1 ) can be achieved by some types of temporary passivation. From an extensive review of available data in the literature, we find p-type silicon can be best passivated by hydrofluoric acid containing solutions, with superacid-based thin films showing a slight superiority in the n-type case. We review the practical considerations associated with temporary passivation, including sample cleaning, passivation activation, and stability. We highlight examples of how temporary passivation can assist in the development of improved silicon materials for photovoltaic applications, and provide an outlook for the future of the field.

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Impurity gettering effect of atomic layer deposited aluminium oxide films on silicon wafers

Cited by 25 publications

References 18 publications

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

Transition Metals in a Cast‐Monocrystalline Silicon Ingot Studied by Silicon Nitride Gettering

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

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