Black silicon significantly enhances phosphorus diffusion gettering

• Published in: Scientific reports 2018-01, Vol.8 (1), p.1991-6, Article 1991
• Main Authors: Pasanen, Toni P., Laine, Hannu S., Vähänissi, Ville, Schön, Jonas, Savin, Hele
• Format: Article
• Language: English
• Subjects: 639/301/1005; 639/301/119/1000; 639/624/1075/524; 639/766/119/1000; Diffusion; Humanities and Social Sciences; Impurities; Iron; Low temperature; multidisciplinary; Needles; Phosphorus; Photovoltaics; Science; Science (multidisciplinary); Silicon; Silicon wafers
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-20494-y

Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications. We show here that the increased surface area of b-Si, which has generally been considered as a drawback e.g. in applications that require efficient surface passivation, can be used as an advantage: it enhances gettering of deleterious metal impurities. We demonstrate experimentally that interstitial iron concentration in intentionally contaminated silicon wafers reduces from 1.7 × 10 13  cm −3 to less than 10 10  cm −3 via b-Si gettering coupled with phosphorus diffusion from a POCl 3 source. Simultaneously, the minority carrier lifetime increases from less than 2 μs of a contaminated wafer to more than 1.5 ms. A series of different low temperature anneals suggests segregation into the phosphorus-doped layer to be the main gettering mechanism, a notion which paves the way of adopting these results into predictive process simulators. This conclusion is supported by simulations which show that the b-Si needles are entirely heavily-doped with phosphorus after a typical POCl 3 diffusion process, promoting iron segregation. Potential benefits of enhanced gettering by b-Si include the possibility to use lower quality silicon in high-efficiency photovoltaic devices.