The effect of ambient conditions on thin wafers processed with fs-laser machining

Yield stress of 80 μm thick glass wafer chip diced with fs-laser μ-processing was investigated with varying the repetition rate of laser pulse and scanning speed under constant number of shot. By using constant laser fluence, the yield stress is almost invariant at lower repetition rate less than 20 kHz, but abruptly drops to the half of initial yield stress. Based on the effect of the ambient gas on the transition point of yield stress changes, we propose an empirical relation between the yield stress and cumulative stress caused by temperature increment with changing the laser repetition rate.