How big problem is Cu contamination in crystalline silicon - - PowerPoint PPT Presentation

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How big problem is Cu contamination in crystalline silicon - - PowerPoint PPT Presentation

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How big problem is Cu contamination in crystalline silicon photovoltaics? Hele Savin Aalto University Department of Electronics and Nanoengineering Electron Physics Group Espoo, Finland (population ~ 5 million) 5.10.2019 2 5.10.2019 3

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How big problem is Cu contamination in crystalline silicon photovoltaics?

Hele Savin

Aalto University Department of Electronics and Nanoengineering Electron Physics Group Espoo, Finland

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5.10.2019 2

(population ~ 5 million)

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5.10.2019 3

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5.10.2019 4

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Helsinki School of Economics University of Art & Design Helsinki Helsinki University of Technology

1849 1871 1911

2010

Merger of three leading Finnish universities

12 000

full-time equivalent degree students A staff of about 4 000, of which nearly 400 are professors

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Micronova: Research center in Micro - and Nanotechnology

  • The centre also hosts many

companies

  • Industrial scale facilities, 2600m2
  • f cleanrooms
  • 360 personnel (19 in maintenance)
  • 60 PhD students
  • Over 150 major equipment

installed

  • 150 mm R&D Fab, currently

upgraded to 200 mm

http://www.micronova.fi/

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Micronova: Research center in Micro - and Nanotechnology

http://www.micronova.fi/

F1 Flip-chip Bonding F2 Wet Processing F3 Nanolithography F4 Plasma and Sputtering F5 Plating F6 Metrology F7 Furnace F8 Lithography F9 ALD F10 Plasma F11 Wafers F12 Chemistry F13 Analysis Lab

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Micronova: Research center in Micro - and Nanotechnology

http://www.micronova.fi/

F1 Flip-chip Bonding F2 Wet Processing F3 Nanolithography F4 Plasma and Sputtering F5 Plating F6 Metrology F7 Furnace F8 Lithography F9 ALD F10 Plasma F11 Wafers F12 Chemistry F13 Analysis Lab

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Electron Physics Group

Crystalline silicon PV activities

  • Black silicon
  • DRIE and MACE
  • Electrical simulations
  • IBC/lab and PERC/industry
  • How to explain >100% EQE
  • Black Ge
  • ALD metal oxides
  • Surface passivation, passivated contacts
  • Up-conversion materials
  • Coating of module glasses
  • Light/Carrier induced degradation
  • Cu-LID
  • Mitigation of LeTID

2.2.2016 9

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Use of “PV”-innovations in other fields

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Cast-Mono in MEMS&NEMS

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Use of “PV”-innovations in other fields

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Certified EQE in UV > 130% Cast-Mono in MEMS&NEMS

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Use of “PV”-innovations in other fields

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Utilize LID in Integrated Circuits Certified EQE in UV > 130% Cast-Mono in MEMS&NEMS

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Can we take advantage of this effect somewhere else?

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Reference Cu-contaminated

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Another example how to utilize LID

Fe Cu

Initial t @ high injection

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Another example how to utilize LID

Fe Cu

Initial t @ high injection After light soaking

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Another example how to utilize LID

Fe Cu

Initial t @ high injection After light soaking Nice Cu (and Fe) map !

ECS Trans. 11, 319 (2007)

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Measurement of low-Cu concentrations

  • The strength of degradation depends on Cu

concentration Benefits:

  • Other common impurities such as Fe can be

separated

  • Contactless, non-destructive, fast, sensitive
  • Appl. Phys. Lett. 87, 032109 (2005)
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ref (no Cu) low Cu med Cu high Cu high low

How about mc-Si?

t = 0

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ref (no Cu) low Cu med Cu high Cu high low

How about mc-Si?

t = 2 min

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ref (no Cu) low Cu med Cu high Cu high low

How about mc-Si?

t = 17 min

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ref (no Cu) low Cu med Cu high Cu high low

How about mc-Si?

t = 3 hours

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ref (no Cu) low Cu med Cu high Cu high low

How about mc-Si?

t = 8 hours

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Naturally works with PL too

Cu contaminated spot

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Using PL to measure Cu in Silicon

High lifetime Low lifetime

𝐷𝐷𝑣 ∝ 𝑂𝑢

∗ =

1 τ𝑒𝑓𝑕𝑠𝑏𝑒𝑓𝑒 − 1 τ𝑗𝑜𝑗𝑢𝑗𝑏𝑚

Cu contaminated spot

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The role of oxygen (BMD)

  • Sensitivity can be increased by adding
  • xygen precipitates
  • Detection limit ppt -level
  • Appl. Phys. Lett. 87, 032109 (2005)
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Boron and oxygen certainly helps…

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… but you don’t need them

  • Appl. Phys. Lett. 95, 152111 (2009)

FZ silicon n-type silicon

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What about elevated temperature …?

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Can be used for faster detection Definitely makes the kinetics faster

  • Appl. Phys. Lett. 107, 052101 (2015)
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What about higher intensity …?

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Similarly makes the kinetics faster …. …. further work

  • ngoing on this
  • J. Electrochem. Soc. 150 (12), 2003
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Gettering during POCl3 diffusion?

  • Cu fast diffuser
  • Should be easy to getter
  • … not always true

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AIP Advances 8, 015112 (2018)

Cu

Phosphorus-doped region

Cu Cu

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Gettering during POCl3 diffusion?

  • Cu fast diffuser
  • Should be easy to getter
  • … not always true

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AIP Advances 8, 015112 (2018)

Cu

Phosphorus-doped region

Cu Cu

10 20 30 40 50 Position [mm]

Normal cooling after POCl3 + light soak

170 210 250 290 330 370 410

Diffusion length [m]

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Gettering during POCl3 diffusion?

  • Cu fast diffuser
  • Should be easy to getter
  • … not always true

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AIP Advances 8, 015112 (2018)

Cu

Phosphorus-doped region

Cu Cu

10 20 30 40 50 Position [mm] 10 20 30 40 50 170 210 250 290 330 370 410

Position [mm] Diffusion length [m]

Normal cooling after POCl3 + light soak

170 210 250 290 330 370 410

Diffusion length [m]

Slow cooling after POCl3 + light soak

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How stable is it during firing?

It is not stable, during high-T firing copper diffuses back to the bulk !

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  • Appl. Phys. Lett. 113 (2018)
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Impact of firing temperature?

If firing T is too slow → no Cu-LID Cu prefers to stay in the emitter / surfaces

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  • Appl. Phys. Lett. 113 (2018)
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Impact of ramp rates during firing?

Slow ramp rates reduce Cu-LID Simulations verify that Cu goes to bulk during firing but has time to diffuse back to emitter

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  • Appl. Phys. Lett. 113 (2018)
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Cu in PERC cells?

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INITIALLY AFTER ILLUMINATION

Solar Energy Materials and Solar Cells 186, 373-377 (2018)

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Cu in PERC cells?

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INITIALLY AFTER ILLUMINATION

Solar Energy Materials and Solar Cells 186, 373-377 (2018)

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Quantum efficiency

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Solar Energy Materials and Solar Cells 186, 373-377 (2018)

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Physics behind Cu-LID (+modeling)

  • Cui positively charged, fast diffuser, not

recombination active

  • Cu precipitates positively charged, highly

recombination active

  • Hypothesis: Light changes the charge state of

Cu precipitates → electrostatic attraction

  • All parameters known (diffusivity, solubility,

precipitation kinetics, recombination parameters… )

  • Modeling shows pretty nice correlation with

experiments

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  • H. Vahlman, PhD thesis 2018 and publications there
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Physics behind Cu-LID (+modeling)

  • Cui positively charged, fast diffuser, not

recombination active

  • Cu precipitates positively charged, highly

recombination active

  • Hypothesis: Light changes the charge state of

Cu precipitates → electrostatic attraction

  • All parameters known (diffusivity, solubility,

precipitation kinetics, recombination parameters… )

  • Modeling shows pretty nice correlation with

experiments

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Still cannot see anything here in e.g. TEM / DLTS…

  • H. Vahlman, PhD thesis 2018 and publications there
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What about dark anneal…?

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Solar Energy Materials and Solar Cells 134 (2018)

Formation of recombination active precipitates - supersaturation (fast reaction) Precipitate dissolution – diffusion to surfaces (slow reaction)

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What about dark anneal…?

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Solar Energy Materials and Solar Cells 134 (2018)

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“Le-TID” after dark anneal

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Solar Energy Materials and Solar Cells 134 (2018)

No LeTID after long dark anneal

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“Le-TID” after dark anneal in PERC

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Silicon PV 2019

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What about hydrogenation…?

All the prior results have been carried out without PECVD SiNx:H, so we don’t know … yet

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Conclusions

  • LID can be also a positive issue
  • Measurement of Cu contamination
  • Enhancing Cu gettering in microelectronics
  • Cu can cause severe LID in solar cells – be aware of

contamination risks

  • It may be difficult to separate Cu-LID from other LID

mechanisms …

  • Looking forward to further collaborations with UNSW!

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2.2.2016 46

Thank you!

Funding acknowledgements: