Selective Laser-induced EtchingCopyright: Fraunhofer ILT
Micro structures inside transparent materials are fabricated by Selective Laser-induced Etching SLE
Selective Laser-induced Etching (SLE)
Selective Laser-induced Etching (SLE) is a new production technology for the fabrication micro parts, channels and shaped cuts in transparent materials like glass or sapphire.
The miniaturization of products in micro optics, medical technology and micro system technology requires transparent components with structure sizes in the micrometer range and accuracies of about 100 nm. SLE is an appropriate manufacturing process for micro machining of transparent materials such as sapphire and glasses, e.g. fused silica. By focusing the laser radiation in the volume the material is locally modified. For example, the crystalline structure of sapphire is transfomed into a amorphous vitreous structure, which can be etched 10,000 times faster by wet etching with KOH or HF. By scanning the laser focus with pulse overlap inside the material, connected volumes of modified material are created. The modified volumes are subsequently removed by chemical etching using aqueous solution of e.g. HF or KOH.
By means of SLE micro-channels with large aspect ratio are produced in glasses and sapphire.
Slits of 1 µm width, 125 µm height and 10 mm length with surface qualities < 100 nm are cut in sapphire.
Furthermore, by selectively modifying a closed plane in fused silica and subsequent etching both the micro component and the shaped hole result with a kerfs width of < 10 µm. The roughness of the cut planes is very low, e.g. the peak to peak roughness Rz ~ 1 µm.
Currently available high speed scanning systems based on galvo mirrors are equipped with objectives with small numerical apertures (NA<0.2) not sufficient for most of the in-volume micro structuring processes. Whereas high precision air bearing translation stages are used with microscope objectives the speed is limited to approximately 100 mm/s. In order to overcome these limitations a galvo scanner we have build a microscanner with large maximum scanning velocity (50-400 mm/s), large numerical aperture (NA=0.4-1.2), small focus size (0.6-2.2 µm), high precision (100-400 nm) and computer controlled pre-compensation of spherical aberrations for in-volume focusing. Furthermore, the microscanner is combined with a computer controlled three axis translation stage to process large flat work pieces such as wafers up to 2 mm in thickness.