Distribution of iron in multicrystalline silicon ingots

Kvande, R.; Geerligs, L.J.; Coletti, Gianluca; Arnberg, L.; Sabatino, Marisa Di; Øvrelid, Eivind; Swanson, C. C.

doi:10.1063/1.2956697

Cited by 46 publications

(46 citation statements)

References 30 publications

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“…The samples from the bottom were selected տ3 cm above the crucible bottom to avoid the regions where contamination from solid-state in-diffusion from the crucible dominates the metal distribution. Interpolating the neutron activation analysis (NAA) data from the CrystalClear project, 42,43 the iron concentrations for the samples are estimated to be: 3:3 Â 10 13 ; 3 Â 10 13 ; 6 Â 10 14 for the 53 ppmw ingot and Three sister wafers were pulled out of the processing line at each of the three heights in both ingots: one as-cut, one after gettering, and one following SiN x deposition and firing. 12 The phosphorus diffusion process was a standard industrial process conducted in a POCl 3 tube furnace.…”

Section: Methodsmentioning

confidence: 99%

“…Extensive data on the macroscopic distribution of iron and its effect on performance in these samples have already been published. 12,42,43 The samples were selected from a relative ingot height of 29%, 61%, 88% and 30%, 68%, and 85% for the 53 and 200 ppmw Fe ingots, respectively. The wafers from these heights will be subsequently referred to as "Bottom," "Middle," and "Top."…”

Section: Methodsmentioning

confidence: 99%

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Precipitated iron: A limit on gettering efficacy in multicrystalline silicon

Fenning

Hofstetter

Bertoni

et al. 2013

Journal of Applied Physics

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A phosphorus diffusion gettering model is used to examine the efficacy of a standard gettering process on interstitial and precipitated iron in multicrystalline silicon. The model predicts a large concentration of precipitated iron remaining after standard gettering for most as-grown iron distributions. Although changes in the precipitated iron distribution are predicted to be small, the simulated post-processing interstitial iron concentration is predicted to depend strongly on the as-grown distribution of precipitates, indicating that precipitates must be considered as internal sources of contamination during processing. To inform and validate the model, the iron distributions before and after a standard phosphorus diffusion step are studied in samples from the bottom, middle, and top of an intentionally Fe-contaminated laboratory ingot. A census of iron-silicide precipitates taken by synchrotron-based X-ray fluorescence microscopy confirms the presence of a high density of iron-silicide precipitates both before and after phosphorus diffusion. A comparable precipitated iron distribution was measured in a sister wafer after hydrogenation during a firing step. The similar distributions of precipitated iron seen after each step in the solar cell process confirm that the effect of standard gettering on precipitated iron is strongly limited as predicted by simulation. Good agreement between the experimental and simulated data supports the hypothesis that gettering kinetics is governed by not only the total iron concentration but also by the distribution of precipitated iron. Finally, future directions based on the modeling are suggested for the improvement of effective minority carrier lifetime in multicrystalline silicon solar cells.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Precipitated iron: A limit on gettering efficacy in multicrystalline silicon

Fenning

Hofstetter

Bertoni

et al. 2013

Journal of Applied Physics

Self Cite

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“…Therefore, this would indicate that the efficiency decrease of solar cells made of wafers sliced from the top sections of the ingot is mostly dominated by the defect generation during the crystal growth. Indeed, it is well-known that the distribution of the Fe contamination, mostly entering the melt by solid-state diffusion from the crucible and silicon nitride coating, tends to move from interstitial to precipitated [8,9], from bottom to top of the ingot. Thus, in order to investigate this effect on mono-like wafers, Figure 5(a) illustrates the evolution of [FeJ before and after a typical phosphorus gettering (PDG) process.…”

Section: Industrial Manufacturing Of Mono-like Ingots Experimental Fmentioning

confidence: 99%

About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

Guerrero

Parra

Carballo

et al. 2012

Prog. Photovolt: Res. Appl.

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The era of the seed-cast grown monocrystalline-based silicon ingots is coming. Mono-like, pseudomono or quasimono wafers are product labels that can be nowadays found in the market, as a critical innovation for the photovoltaic industry. They integrate some of the most favorable features of the conventional silicon substrates for solar cells, so far, such as the high solar cell efficiency offered by the monocrystalline Czochralski-Si (Cz-Si) wafers and the lower cost, high productivity and full square-shape that characterize the well-known multicrystalline casting growth method. Nevertheless, this innovative crystal growth approach still faces a number of mass scale problems that need to be resolved, in order to gain a deep, 100% reliable and worldwide market: (i) extended defects formation during the growth process; (ii) optimization of the seed recycling; and (iii) parts of the ingots giving low solar cells performance, which directly affect the production costs and yield of this approach. Therefore, this paper presents a series of casting crystal growth experiments and characterization studies from ingots, wafers and cells manufactured in an industrial approach, showing the main sources of crystal defect formation, impurity enrichment and potential consequences at solar cell level. The previously mentioned technological drawbacks are directly addressed, proposing industrial actions to pave the way of this new wafer technology to high efficiency solar cells.

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“…In addition, the time-dependent Fe-B dissociation signal has been used on wafers for the measurement of the interstitial iron concentration [26]. Interestingly, the total iron concentration can be orders of magnitude higher [3], [12], [18] than the interstitial concentration due to a large fraction of precipitated iron and is assessable most sensitively via neutron activation analysis or various mass spectroscopy measurements including GDMS, SIMS, or ICPMS [17], [18], [27]. Interstitial iron is highly mobile in the silicon lattice at elevated temperatures during diffusion and firing [9], [28].…”

mentioning

confidence: 99%

“…In the past, height profiles were usually measured via the analysis of a series of wafers [17], [18]. Only recently different approaches measuring lifetimes directly on the brick surface had been demonstrated.…”

mentioning

confidence: 99%

Imaging As-Grown Interstitial Iron Concentration on Boron-Doped Silicon Bricks via Spectral Photoluminescence

Mitchell

Macdonald

Schön

et al. 2014

IEEE J. Photovoltaics

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Abstract-The interstitial iron concentration measured directly on the side face of a silicon brick after crystallization and brick squaring can give important early and fast feedback regarding its material quality. Interstitial iron is an important defect in crystalline silicon, particularly in directionally solidified ingots. Spectral photoluminescence intensity ratio imaging has recently been demonstrated to independently provide high-resolution bulk lifetime images and is therefore ideally suited to assess spatially variable multicrystalline silicon bricks. Here, we demonstrate this technique to enable imaging of the interstitial iron concentration on boron-doped silicon bricks and thick silicon slabs. We present iron concentration studies for two directionally solidified silicon bricks of which one is a standard multicrystalline and the other is a seeded-growth ingot. This lifetime-based measurement technique is highly sensitive to interstitial iron with detection limits down to concentrations of about 1 × 10 10 cm −3 . Its accuracy is enhanced, as the injection level remains below 2 × 10 12 cm −3 during the measurement and, hence, avoids the influence of injection level dependences on the conversion factor, although it remains dependent on the knowledge of the electron capture cross section of interstitial iron in silicon. Access to both bulk lifetime and dissolved iron concentration provides a valuable parameter set of as-grown crystal quality and the relative recombination fraction of interstitial iron via Shockley-Read-Hall (SRH) analysis. Simulated interstitial iron concentration profiles support the presented experimental data.Index Terms-Bricks, dissolved iron, imaging, ingot, interstitial iron, photoluminescence (PL), silicon.

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Distribution of iron in multicrystalline silicon ingots

Cited by 46 publications

References 30 publications

Precipitated iron: A limit on gettering efficacy in multicrystalline silicon

Precipitated iron: A limit on gettering efficacy in multicrystalline silicon

About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

Imaging As-Grown Interstitial Iron Concentration on Boron-Doped Silicon Bricks via Spectral Photoluminescence

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