CRACK INVESTIGATION IN MONOCRYSTALLINE SILICON BEFORE AND AFTER ANNEALING C. Klute 1,2 , L. Lam 1,3 , S. Schoenfelder 1,2 , J. Bagdahn 1 1 Fraunhofer Center for Silicon Photovoltaics, Halle, Germany 2 Fraunhofer Institute for Mechanics of Materials, Halle, Germany 3 Massachusetts Institute of Technology, Cambridge, USA carola.klute@csp.fraunhofer.de ABSTRACT In industrial manufacturing of solar cells, based on silicon wafers, breakage rate plays an important role, since material have a significant fraction of overall photovoltaic module manufacturing costs. By increasing the strength of wafers being processed, breakage rate can be minimized, resulting in economic benefits. The strength of as-cut wafers can be increased by applying annealing at 600°C or below. This work investigates the influence of annealing on defined cracks in monocrystalline silicon after Vickers indentation. It is shown, that strength can be increased after a temperature step if the region of plastic deformation is still present. For samples with cracks and removed plastically deformed region no significant increase of strength was observed. 1 INTRODUCTION For a large number of applications in photovoltaics and microelectronics industry, the brittle semiconductor material silicon is used. During the industrial manufacturing of solar cells, based on silicon wafers, breakage rate plays an important role, since material costs significantly influence the costs of a solar cell. If strength of wafers can be increased, the breakage rate can be reduced, reducing manufacturing costs. In literature it can be found, that annealing steps can be used for different reasons to influence the material properties of silicon in photovolatics. Rinio et al. [1] showed that by annealing at 500°C the efficiency of multicrystalline solar cells can be increased. Another option for the application of annealing is as a gettering method to change defect distributions across a wafer thickness [2]. Yasutake et al. [3] showed, that strength of chemically polished, monocrystalline {100} orientated silicon wafers can be increased by annealing in oxygen for temperature above 700°C, while annealing in vacuum has shown no effect on strength. In contrast, it could be shown in experiments recently, that the strength of monocrystalline and multicrystalline as-cut wafers after wire-sawing significantly increases by applying certain annealing steps using different temperature profiles in a range from 200°C to 1000°C in an argon atmosphere [4], which can be seen in Figure 1. In those tests identical batches of wafers were fractured after various annealing temperatures using a 4-point bending setup. The tests were performed at room temperature in ambient environment.