Abstract
This paper analyzes laser and etching parameters to fabricate open and continuous microchannels and stacks of such microchannels in the bulk of crystalline sapphire (α-Al2O3). The structures are produced using a two-step method consisting of laser irradiation and selective etching. Infrared femtosecond laser pulses are focused in the bulk to locally render the crystalline material into amorphous. The amorphous material is, then, selectively etched in hydrofluoric acid. Amorphous sapphire shows a high etching selectivity in comparison to its crystalline state, which makes this material very attractive for a use with this technique. However, some of its properties make the processing challenging, especially during the laser-induced amorphization phase. This paper studies the effect of laser parameters by a step-by-step approach to fabricate long structures (longest dimensions up to millimeters) of different shapes inside the bulk of sapphire. The minimum cross-sectional dimensions of the resulting structures (microchannels) vary from few hundreds of nanometers for the smallest channels to tens of micrometers for the largest stacks of microchannels. The effect of the variation of repetition rate, pulse energy and channel-to-channel distance on the microchannels and stacks of microchannels is studied. SEM micrographs of polished cross-sections are used for performing a quantitative and qualitative analysis of the morphology of the structures after laser irradiation and, subsequently, after selective wet chemical etching.
Highlights
Crystalline sapphire (α-Al2O3) is nowadays used as construction component or base material in many sectors of science and technology
Processing of sapphire has been demonstrated using different methods: direct laser writing [15,16], mechanical sawing [17], dry and wet etching [21,22,23]. In this manuscript we study a two-step method consisting of laser irradiation of crystalline sapphire with consequent modification of the exposed material into amorphized material and successive selective removal of the latter by wet etching
If femtosecond or picosecond laser pulses are used with intensities in the order of 1013–1014 W/cm2 [24,25,26] absorbed laser energy [27] leads to the amorphization of the crystalline sapphire
Summary
Crystalline sapphire (α-Al2O3) is nowadays used as construction component or base material in many sectors of science and technology. Processing of sapphire has been demonstrated using different methods: direct laser writing [15,16], mechanical sawing [17], dry (plasma etching [18,19,20]) and wet etching [21,22,23]. In this manuscript we study a two-step method consisting of laser irradiation of crystalline sapphire with consequent modification of the exposed material into amorphized material and successive selective removal of the latter by wet etching. If the material is exposed to several, overlapping laser pulses, it is possible to create regions and volumes of amorphized material
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