How to Obtain Solderable Al/Ni:V/Ag Contacts

Lehr, Martin; Heinemeyer, Frank; Eidelloth, S.; Brendemühl, Till; Kiefer, Fabian; Münster, Daniel; Lohse, Anja; Berger, M. N.; Braun, Nadja; Brendel, Rolf

doi:10.1016/j.egypro.2013.07.292

Cited by 5 publications

(2 citation statements)

References 4 publications

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“…However, more process steps are involved for PVD Al metallization, as shown in Figure . Moreover, in order to achieve a good solder contact to the PVD Al on full rear side, depositing a double layer of Ni : V/Ag with respective thickness of 200 and 25 nm on top of PVD Al layer is necessary . To simplify its fabrication process, the future work will focus on eliminating: (i) the short time buffered oxide etch cleaning, for example, by further reducing surface damages with optimized laser parameters and performing the laser patterning in an inert ambient to avoid the thin SiO 2 layer grown in the vias during ablation; (2) the in situ Ar plasma etching, for example, by processing the front contact firing in N 2 ambient to avoid the thin SiO 2 layer grown in the vias; and (iii) the post‐PVD anneal, for example, by increasing the deposition temperature during the PVD.…”

Section: Resultsmentioning

confidence: 99%

“…Because the sheet resistance of a 2‐µm‐thick PVD Al layer is just ~0.015 Ω/□ , a thin (1 ~ 2 µm) PVD Al layer on the entire rear area is sufficient to meet the required electrical conductance for large‐area Si solar cells, which further leads to less wafer bow and less Al consumption . On the other hand, in order to obtain a good solder contact to the PVD Al side, depositing a double layer of Ni : V/Ag with respective thickness of 200 and 25 nm on top of PD Al layer can offer an excellent solderability with a peel force greater than 3 N/mm and long‐term stability . Moreover, to improve the mass production cost of PVD Al process, the industrial pilot PVD machine with throughput of over 500 wafers per hour has also been demonstrated .…”

Section: Introductionmentioning

confidence: 99%

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20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

Tao

Payne

Upadhyaya

et al. 2014

Progress in Photovoltaics

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In this work, we report on ion-implanted, high-efficiency n-type silicon solar cells fabricated on large area pseudosquare Czochralski wafers. The sputtering of aluminum (Al) via physical vapor deposition (PVD) in combination with a laserpatterned dielectric stack was used on the rear side to produce front junction cells with an implanted boron emitter and a phosphorus back surface field. Front and back surface passivation was achieved by thin thermally grown oxide during the implant anneal. Both front and back oxides were capped with SiN x , followed by screen-printed metal grid formation on the front side. An ultraviolet laser was used to selectively ablate the SiO 2 /SiN x passivation stack on the back to form the pattern for metal-Si contact. The laser pulse energy had to be optimized to fully open the SiO 2 /SiN x passivation layers, without inducing appreciable damage or defects on the surface of the n + back surface field layer. It was also found that a low temperature annealing for less than 3 min after PVD Al provided an excellent charge collecting contact on the back. In order to obtain high fill factor of~80%, an in situ plasma etching in an inert ambient prior to PVD was found to be essential for etching the native oxide formed in the rear vias during the front contact firing. Finally, through optimization of the size and pitch of the rear point contacts, an efficiency of 20.7% was achieved for the large area n-type passivated emitter, rear totally diffused cell.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

Tao

Payne

Upadhyaya

et al. 2014

Progress in Photovoltaics

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Low-temperature Interconnection of PVD-Aluminium Metallization

et al. 2016

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Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

Kumm

Samadi

Chacko

et al. 2016

Journal of Applied Physics

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An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al 2O3 layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells

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How to Obtain Solderable Al/Ni:V/Ag Contacts

Cited by 5 publications

References 4 publications

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

Low-temperature Interconnection of PVD-Aluminium Metallization

Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

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