Groove Morphology and Debris Height in Femtosecond Laser Grooving of SiCOH Low-k Wafers Under Infrared and Ultraviolet Processing Conditions

Femtosecond laser grooving is used as a pre-processing step ahead of the mechanical dicing of low-k dielectrics, which are brittle and prone to cracking and delamination under stress. To relate the groove geometry and the debris height to the processing parameters, SiCOH low-k wafers were grooved at a fixed pulse duration of 250 fs under an infrared condition at 1030 nm and an ultraviolet condition at 343 nm, with nominal spot diameters of 12 and 7 µm, respectively. Each groove was formed in eight passes. The groove width (rim-to-rim), depth, and maximum debris height were measured over 18 combinations of pulse frequency and scan speed for each condition and analyzed in terms of peak fluence and pulses per spot, the accumulated number of pulses per unit area. The ultraviolet condition produced narrower and shallower grooves with a lower maximum debris height than the infrared condition, and the difference was largest for debris height. The mean groove depth exceeded the approximately 1 µm film thickness in all conditions, i.e., on average the grooves extend into the silicon substrate. For both conditions, debris height showed its strongest correlation with pulses per spot (r = +0.91 and +0.81, p < 0.001), also when the three measurement positions were analyzed separately. A higher scan speed, which lowers the pulses per spot, was associated with a lower maximum debris height, a relation that may serve as a reference for selecting the pulse frequency and the scan speed.