Variation in the Etch Rate of LIBWE Fabricating Deep Microtrenches

were fabricated with a fluence of 1.3 J/cm 2 , a pulse repetition of 80 Hz, and various pulse numbers. Special care was directed to maintaining in-focus conditions for etching. In the fabrication of 5-µmwide microtrenches, etch rates of 5.3 nm/pulse evaluated for trenches with depths of less than 4 µm increased by a factor of 2.55 to 13.5 nm/pulse when the trenches became deeper than 16 µm. Such variation in the etch rate reduced with width and became negligibly small for 20-µm-wide microtrenches. Based on a similar dependence on width, the variation in etch rate with depth can be related to the size effect observed in LIBWE. As a factor causing the size effect as well as the variation in etch rate with depth, the interaction between the laser-heated surface and the solution in an early time region of the laser-induced phenomena is proposed.