Plasma etched initial pits for electrochemically etched macroporous silicon structures

Macroporous silicon structures of different shapes were prepared by electrochemical etching of n-type silicon in diluted HF under illumination. Depths reaching 80 mum and 40:1 aspect ratios were achieved. A PECVD amorphous silicon layer was used as a masking layer. Undoped amorphous silicon was found to be quite resistant to the HF etching solution. The initial pits were prepared by reactive ion etching (RIE) instead of the conventional anisotropic alkaline wet etching. The advantages of RIE-made initial pits were demonstrated by electrochemically etched Fresnel lenses. Electrochemically etched complex trenches with curved shapes have been demonstrated for the first time. Illumination modulation was employed to fabricate arrays of macropores with variable diameters and free-standing macroporous film.