Characterization of Laser Induced Charging Damage in Laser Micromachining

Laser induced damage has been observed from laser micromachining of Si with insulating material on device structures. Characterization of damage suggests the potential mechanism as laser induced charging damage. Static measurements using a Langmuir type probe for measuring average spatial charge distributions, accumulated charges, and maximum current are conducted to understand the charge characteristics of laser micromachining on Si and on insulating layer/Si. The amount of charge accumulating on the probe is seen to be proportional to the increase in laser energy, repetition rate, spatial overlap, and probe bias. Machining of insulating layer coating on Si shows the accumulation of positive charge while machining of bare Si indicates cumulative small positive or negative charges depending on the location of the probe. Hydrofluorocarbon (HFC) assisted ablation generates an order of magnitude smaller amount of charge compared to no assist ablation. Spatial charge profiles show a rapidly decaying distribution with distance away from ablation region and a fit of these data to a cos n function shows an increasing value of n as a function of distance from the wafer surface.