Femtosecond laser micromachining of an Au/Cr film nanostack

Selective laser patterning of thin films in a multilayer structure is an emerging technology for the fabrication of MEMS devices. A 775-nm Ti:sapphire laser (130 fs, 1 kHz) was used to irradiate thin-film stacks with variations in the process parameters, such as the pulse energy, feed rate, and numerical aperture of the objective lens. The two layers of the Au/Cr film have the same thickness, which is about 1000 nm. They were coated on a glass substrate. By SEM, an AFM and an optical surface profiler, we investigate the morphology of a pattern including the line width, groove depth, and laser-induced periodic surface structures (LIPSSs). The ablation depth was observed to depend on the pulse energy. In addition, from the energy spectrum, we find which layer was removed completely. The experimental results show that precise micromachining with a desired stability and reproducibility can be achieved by controlling the ablation energy and the feed rate. With a different energy and feed rate, we have processed the gating and the circle, which with the smooth cutting edge and groove was consistent with the beam spatial distribution.