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4 March 2019 Laser induced crystal defects in monocrystalline silicon
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We investigate the conditions for the formation of crystal defects leading to residual stress after spot laser melting of monocrystalline silicon with microsecond laser pulses. With the help of micro-Raman spectroscopy and Secco defect etching, we find a sharp transition from dislocation free to dislocation rich recrystallization corresponding to a threshold laser pulse energy Ep, for a given laser pulse length τp and focus diameter df. Besides the dependence of the threshold Ep on τp and df, our experiments show a strong dependence on the crystal orientation. The f100g-oriented substrates resist laser pulses with a two times higher laser pulse energy than the {111}- or {110}-oriented substrates. Using electron backscatter diffraction (EBSD), we find evidence for the formation of grain boundaries parallel to the appearance of pores within the melt pool. The pores most likely form when the oxygen solubility in the melt and the resolidified material decreases during cool down and the excess oxygen leaves, forming vapor pores. Avoiding oxygen uptake from the environment by processing under vacuum conditions at p = 1 mbar ambient pressure, prevents both, pores and grain boundaries.
Conference Presentation
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T. Menold, F. Lanoy, M. Ametowobla, S. Hinderberger, K. Ohmer , J. R. Köhler , and J. H. Werner "Laser induced crystal defects in monocrystalline silicon", Proc. SPIE 10905, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXIV, 109050X (4 March 2019); doi: 10.1117/12.2508686;

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