A novel micromachining technique for silicon deep anisotropic etching using macroporous silicon is developed. Macroporous silicon is formed selectively in n-type substrates using silicon anodization in a hydrofluoric acid (HF)-based electrolyte with backside illumination. Three-dimensional microstructures are fabricated by removing the macroporous silicon in alkali solutions. This technique enables us to etch (100) n-type silicon with arbitrary shaped windows to produce high-aspect-ratio structures with vertical sidewalls using a wet etching process.
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