Improved Surface Cleaning by In Situ Hydrogen Plasma for Amorphous/Crystalline Silicon Heterojunction Solar Cells

Abstract:

In future, thin wafers (< 100µm) will be employed in silicon heterojunction solar cell to decrease modules cost-per-Watt-Peak. However, in order to maintain excellent cell efficiency a higher device surface/volume ratio will demand stricter requirements on surface passivation. In this frame, the status of the crystalline surface (c-Si) prior to amorphous silicon (a-Si:H(i)) plasma deposition (PECVD) plays an important role: the c-Si chemical termination influences the quality of the interface layer a-Si:H(i)/c-Si, and affect the open circuit voltage (V_oc). Previous studies have shown that smooth and fully hydrogenated c-Si surface [ lead to best quality heterojunction. These surfaces can be obtained by different wet cleaning procedures, usually terminated by an immersion in diluted HF. However, after this step, the wafer surface is highly reactive and can re-oxidize rapidly: contaminants presents in air can be adsorbed and affect wafer passivation [. For this reason, in-situ Hydrogen (H₂) plasma cleaning prior to a-Si:H(i) deposition might be an interesting option to decrease the amount of contaminant on the surface. However, the experimental window is extremely narrow, since phenomena like epitaxial growth and ion-bombardment damage can easily occur [[ and worsen the surface passivation operated by a-Si:H(i) layers. In this contribution, we present an in-situ H₂ plasma clean and show a decrease of Oxygen and Carbon on wafer surface after a short time (<10 sec), without detrimental effects on the subsequent passivation.

• Periodical: Solid State Phenomena (Volume 195)
• Pages: 321-323
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.195.321
• Online since: December 2012
• Authors: Stefano Nicola Granata, Twan Bearda, Frederic Dross, Ivan Gordon, Jef Poortmans, Robert P. Mertens
• Keywords: Amorphous Silicon Passivation, Hydrogen Plasma, Surface Cleaning

References

[1] H. Angermann, F. Wünsch, M. Kunst, A. Laades, U. Stürzebecher, E. Conrad, L. Korte, and M. Schmidt, Effect of wet-chemical substrate pretreatment on electronic interface properties and recombination losses of a -Si: H/c -Si and a -SiNx: H/c -Si hetero-interfaces, physica status solidi (c), vol. 8, no. 3, p.879–882, (2011).

DOI: 10.1002/pssc.201000236

[2] M. Morita, T. Ohmi, E. Hasegawa, M. Kawakami, and M. Ohwada, Growth of native oxide on a silicon surface, Journal of Applied Physics, vol. 68, no. 3, p.1272, (1990).

DOI: 10.1063/1.347181

[3] Z. -H. Zhou, E. S. Aydil, R. A. Gottscho, Y. J. Chabal, and R. Reif, Real-Time, In Situ Monitoring of Room-Temperature Silicon Surface Cleaning Using Hydrogen and Ammonia Plasmas, Journal of The Electrochemical Society, vol. 140, no. 11, p.3316–3321, (1993).

DOI: 10.1149/1.2221029

[4] M. Tucci, E. Salurso, F. Roca, and F. Palma, Dry cleaning process of crystalline silicon surface in a—Si: H/c—Si heterojunction for photovoltaic applications, Thin Solid Films, vol. 403–404, p.307 – 311, (2002).

DOI: 10.1016/s0040-6090(01)01645-5

[5] G. E. Jellison and F. A. Modine, Parameterization of the optical functions of amorphous materials in the interband region, Appl. Phys. Lett., vol. 69, no. 3, p.371–373, Jul. (1996).

DOI: 10.1063/1.118064

[6] S. J. Pearton, Hydrogenated Amorphous Silicon, by R. A. Street, Cambridge University Press, Cambridge 1991, XIV, 417 pp., hardcover, £ 65. 00; ISBN 0-521-37156-2, Advanced Materials, vol. 4, no. 4, p.306–306, (1992).

DOI: 10.1002/adma.19920040419

[7] B. Anthony, T. Hsu, L. Breaux, R. Qian, S. Banerjee, and A. Tasch, Very low defect remote hydrogen plasma clean of Si (100) for homoepitaxy, Journal of Electronic Materials, vol. 19, no. 10, p.1027–1032, Oct. (1990).

DOI: 10.1007/bf02651977