Combined-environment influence on microcrack evolution in mono-crystalline silicon

Abstract

The impact of combined environment conditions (mechanical state, temperature, and relative humidity) on microcrack propagation characteristics in p-type monocrystalline, photovoltaic-grade Si wafers was examined. A four-point bend apparatus was used to impose static strain conditions in 280 micron thick monocrystalline Si wafers containing microindentation-initiated crack centers. The specimen under test was simultaneously subjected to varied temperature and relative humidity conditions within a controlled environment chamber. Microcrack length was monitored after exposure to two sets of temperature and relative humidity conditions (i.e. 20℃ and 33%, 40℃ and 60% respectively) using scanning electron microscopy. Two primary stages of crack elongation behavior were observed under both of the combined environment conditions. Specifically, an early-time, more rapid growth period occurred, followed by more limited crack growth at later times. The deceleration of crack propagation is consistent with stress relaxation accompanying crack elongation under the constant strain conditions imposed. In general, an increase in the average microcrack propagation rate within both growth rate ranges and in the final overall change in average crack length was observed under elevated temperature and humidity conditions. These findings support the probable role of local crack-tip environment on microcrack evolution.