Achievement of Very Smooth Cavity Sidewalls by UV Picosecond Laser Micromachining

As a contactless and maskless method generating a reduced heat affected zone compared to nanosecond laser, ultrafast laser micromachining is widely used for rapid prototyping and materials processing [1]. Today, most research and development works is devoted to study and control LIPPS occurring at the surface of the cavity bottom [2]. But for many applications, there is a strong need to produce highly smooth sidewalls like for microelectronic sample preparation [3], microfluidics [4], waveguides [5], etc.. A laser based technology allowing to obtain very smooth surfaces (Ra of ~3 nm) already exists [6] but it involves melting of a significant volume of material. So far, to the best of our knowledge, no parametric study aiming at minimizing the roughness of picosecond laser micromachined sidewalls in silicon has been performed.