Three-dimensional excimer laser micromachining using greyscale masks

Greyscale masks have been successfully implemented in an excimer laser micromachining system to produce structures with a continuous profile. During this work, it was found possible to machine structures to depths of several tens of microns with no observable mask degradation. The greyscale mask transmissions were defined using a matrix of pixels whose dimension was smaller than the resolution limit of the optical system in the laser micromachining system. By reduction-projecting the greyscale mask pattern onto the workpiece, the local fluence at the workpiece could be predetermined and hence the local machining rates controlled. This enabled three-dimensional (3D) structures to be fabricated at the workpiece in a single machining operation. Under the experimental conditions used in this investigation, the rate at which material was ablated was found to depend linearly on the percentage transmission of the mask. Various test structures, including complex 3D-contoured fluidic channels, have been produced.