HF-free and fast fabrication of long, rectangular microchannels in fused silica: Novel femtosecond laser irradiation geometry

We report the fabrication of truly rectangular buried microchannels of record lengths in fused silica, using a novel femtosecond laser irradiation geometry, at 1030 nm, followed by chemical etching in hot KOH alone. As the result of a judicious choice of the laser parameters and writing geometry, an effective chemical etching rate of 500 μm per hour in the laser irradiated region is achieved, competing with the traditional and hazardous HF based etching, and faster than all earlier reports with KOH. This has resulted in the longest reported (6 mm) rectangular, microchannels, in a record etching time of 6 h. Linear and Cross microchannels have been fabricated with mean surface roughness less than 200 nm of the sidewalls. These results have been validated using an optical microscope, SEM and AFM imaging. The use of fused silica, the much eased safety concerns with KOH, the simplicity of our method, together with the enhanced ability to image from the top surface of smooth, rectangular, buried micro-channels, will motivate microfluidics for Optofluidic lab-on-chip applications, especially for biomedical diagnostics. • HF-free, safe etching using hot KOH alone. • Effective etching rate of 500 μm/h, fastest reported till date. • Great reduction in the channel fabrication time (Laser writing time). • Channel width from 50 μm to 500 μm, all in 6 h. • Mean side wall surface roughness <200 nm. • Validation using Optical imaging, SEM and AFM.