Quasi-pyramidal texturing using phase-segregated masks
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Quasi-pyramidal texturing using phase-segregated masks Katherine L. Saenger, Roy Carruthers, Keith E. Fogel, and Daniel Inns IBM Semiconductor Research and Development Center, Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT Surface texturing processes for thin silicon solar cells ideally remove as little Si as possible relative to amount of topography generated. Here we describe how a micron-scale quasi-pyramidal texture may be achieved in Si layers with arbitrary crystallinity using a phase-segregated mask in combination with reactive ion etching (RIE). The Si to be textured is coated with a thin barrier layer followed by a layer of Al-Si alloy which phase-segregates into micron-sized regions of Al and Si after low temperature (800 for the phase-segregated mask texture). Even lower reflectance values may easily be realized with the use of standard SiO2 or SiN antireflection coatings.
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Fig. 10. Reflectivity of three Si samples: an untextured reference (A), the random pyramids of Fig. 2 (B), and sample 3 of Fig. 9 (C). Note the x400 scale of the dashed and dotted traces.
CONCLUSION Si texturing has been accomplished using Al-Si phase segregated masks in combination with CF4/O2 reactive ion etching. While the resulting texture is reasonably satisfactory, the irregularity of the initial mask shapes can leave a less-than-optimum mix of (i) full-height flat-topped features and (ii) shorter, pointy features reduced in height by excessive undercutting. Improved results can be expected for phase-segregated masks having a narrower distribution of feature sizes. ACKNOWLEDGMENT IBM Microelectronics Research Laboratory (MRL) personnel for help with sample preparation. REFERENCES 1. D.L. King and M.E. Buck, Proc. 22nd IEEE Photovoltaics Specialists Conference, p. 303 (IEEE, New York, 1991). 2. A.W. Blakers, A. Wang, A.M. Milne, J. Zhao, and M.A. Green, Appl. Phys. Lett. 55 1363 (1989). 3. H. L. Chen, S. Y. Chuang, C. H. Lin, and Y. H. Lin, Optics Express 15 14793 (2007). 4. O. Gunawan, K. Wang, B. Fallahazad, Y. Zhang, E. Tutuc and S. Guha, Prog. PVRA 18 (2010). 5. K. Fukutani K. Tanji, T. Saito, and T. Den, J. Appl. Phys. 98 033507 (2005).
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