Modeling of light-induced degradation due to Cu precipitation in p-type silicon. II. Comparison of simulations and experiments

Vahlman, Henri; Haarahiltunen, Antti; Kwapil, Wolfram; Schön, Jonas; Inglese, Alessandro; Savin, Hele

doi:10.1063/1.4983455

Cited by 17 publications

(20 citation statements)

References 46 publications

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“…For simplicity, the precipitates were modeled in this work as spheres. As will be shown in Paper II 76 of this article, satisfactory agreement with experiments is obtained with this assumption, showing that at least the effective behavior can be reproduced with the spherical shape.…”

supporting

confidence: 73%

“…Since time evolution and injection dependence of the BO defect-limited minority carrier lifetime are currently well known, 26,45,46 combining this information with the present model enables the reproduction of full LID curves, that is, minority carrier lifetime as a function of illumination time when both Cu-LID and BO-LID are present simultaneously as separate defects. 21 The validity of the model is investigated in Paper II 76 of this article, using as examples different earlier published and newly observed unpublished aspects of Cu-LID, including dependence on Cu concentration, temperature, intensity, and doping concentration.…”

Section: 195703-1mentioning

confidence: 99%

“…However, modeling of Cu-LID in mc-Si is complicated by extended defects and grain boundaries that often have uneven lateral distribution, which may for example lead to interstitial Cu accumulation in grain boundaries after Cu indiffusion, or laterally varying nucleation and precipitation behavior. For simplicity, Cu-LID is modeled in this work as a homogeneous precipitation process, and a monocrystalline Si material is used in Paper II 76 for model verification. Here, we note that although homogeneous precipitation is assumed in this work, it does not render the model unusable in the case of materials in which Cu precipitates heterogeneously (e.g., when the density of O precipitates is high), since this can be accounted for material-specifically by lowering the excess energy-related terms DG S and c in Eq.…”

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confidence: 99%

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Modeling of light-induced degradation due to Cu precipitation in p-type silicon. I. General theory of precipitation under carrier injection

Vahlman

Haarahiltunen

Kwapil

et al. 2017

Journal of Applied Physics

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Copper contamination causes minority carrier lifetime degradation in p-type silicon bulk under illumination, leading to considerable efficiency losses in affected solar cells. Although the existence of this phenomenon has been known for almost two decades, ambiguity prevails about the underlying defect mechanism. In Paper I of this two-part contribution, we propose the first comprehensive mathematical model for Cu-related light-induced degradation in p-type silicon (Cu-LID). The model is based on the precipitation of interstitial Cu ions, which is assumed to be kinetically limited by electrostatic repulsion from the growing Cu precipitates. Hence, growth and dissolution rates of individual Cu precipitates are derived from the drift-diffusion equation of interstitial Cu and used in a kinetic precipitation model that is based on chemical rate equations. The kinetic model is interlinked to a Schottky junction model of metallic precipitates in silicon, enabling accurate calculation of the injection-dependent electric field enclosing the precipitates, as well as the precipitate-limited minority carrier lifetime. It is found that a transition from darkness to illuminated conditions can cause an increase in the kinetics of precipitation by five orders of magnitude. Since our approach enables a direct connection between the time evolution of precipitate size-density distribution and minority carrier lifetime degradation under illumination, a procedure for calculating the Cu-LID-related lifetime as a function of illumination time is included at the end of this article. The model verification with experiments is carried out in Paper II of this contribution along with a discussion of the kinetic and energetic aspects of Cu-LID. Published by AIP Publishing.

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Section: 195703-1mentioning

confidence: 99%

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confidence: 99%

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Modeling of light-induced degradation due to Cu precipitation in p-type silicon. I. General theory of precipitation under carrier injection

Vahlman

Haarahiltunen

Kwapil

et al. 2017

Journal of Applied Physics

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“…3 was confirmed to be primarily due to the BO-defect based on its known degradation kinetics, i.e., following the procedure described in Ref. 1.…”

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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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“…6 This phenomenon is referred in literature to as copper-related light-induced degradation (Cu-LID) and recent root-cause investigations have proven that Cu-LID arises from the transformation of interstitial Cu atoms into highly recombination active precipitates in the bulk region of the wafer. [7][8][9][10] Gettering is a well-established technique, by which transition metal impurities are relocated to pre-defined substrate areas where they result less harmful for the device performance. In devices where the wafer bulk represents the region of major relevance for the device performance (e.g.…”

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confidence: 99%

Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation

et al. 2018

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The presence of copper (Cu) contamination is known to cause relevant light-induced degradation (Cu-LID) effects in p-type silicon. Due to its high diffusivity, Cu is generally regarded as a relatively benign impurity, which can be readily relocated during device fabrication from the wafer bulk, i.e. the region affected by Cu-LID, to the surface phosphorus-doped emitter. This contribution examines in detail the impact of gettering by industrially relevant phosphorus layers on the strength of Cu-LID effects. We find that phosphorus gettering does not always prevent the occurrence of Cu-LID. Specifically, air-cooling after an isothermal anneal at 800°C results in only weak impurity segregation to the phosphorus-doped layer, which turns out to be insufficient for effectively mitigating Cu-LID effects. Furthermore, we show that the gettering efficiency can be enhanced through the addition of a slow cooling ramp (-4°C/min) between 800°C and 600°C, resulting in the nearly complete disappearance of Cu-LID effects.

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Modeling of light-induced degradation due to Cu precipitation in p-type silicon. II. Comparison of simulations and experiments

Cited by 17 publications

References 46 publications

Modeling of light-induced degradation due to Cu precipitation in p-type silicon. I. General theory of precipitation under carrier injection

Modeling of light-induced degradation due to Cu precipitation in p-type silicon. I. General theory of precipitation under carrier injection

Rapid thermal anneal activates light induced degradation due to copper redistribution

Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation

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