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We report on crack propagation in CZ silicon wafers grown for photovoltaic (PV) applications at faster growth rates than those typical for 200 mm diameter ingots. Enhanced thermal gradients and point defect/impurity distributions associated with rapid growth produces large localized stresses in the wafer core which impacts the direction of propagating cracks. The stress modified crack behavior deviates considerably from the energetically favorable Si[110]/(111) systems enabling scenarios that behave like a ductile fracture following a radial path. Minority carrier lifetime mapping and microscopic etch pit measurements confirmed the presence of a series of radial oxygen precipitate (OP) rings, which impact the energy transfer process at the expanding crack-tip, thereby modifying the crack stress path. Raman spectroscopy was used to quantify the local stresses due to radial oxygen precipitate variations, whereas TEM studies confirmed the presence of OP's, their influence on defect generation and probable role on crack path deviation.

Nanoindentation was used to stimulate and measure materials processes which occur during the initiation and propagation of micro-crack defects in monocrystalline (100) Si wafers. Silicon amorphization occurs and is accompanied by a monotonic drop in hardness and elastic modulus as the nanoindents approach the micro-crack shank or tip. Identification and profiling of localized phase transitions were obtained in the vicinity of a micro-crack using electron back-scattered diffraction (EBSD) and Raman spectroscopy and indicate that regions of amorphous Si extend for about 10 um at the edges and ahead of a moving crack tip.

In this study, we have used a single nanoindentation probe to simultaneously examine the deformation behavior and electrical properties of both mono- and multi-crystalline PV silicon. During nanoindentation loading and unloading cycles, various pressure induced phase transformations occur both under and in the vicinity of the indentation tip. These phase transformations can be monitored in-situ via signature "pop-in" and "pop-out" events that occur in both electrical I-V and physical indent displacement curves. These events are a function of the Si chemistry, structure, and orientation, which we have examined via simultaneous measurements through a conductive nanoprobe, along with complementary spectroscopic Raman analysis.