Study On The Wet Anisotropic Etching Characteristics Of (100),(110) Silicon

Wet anisotropic etching of silicon substrates is commonly used in micromechanics for fabrication of different MEMS structures including membranes, suspended beams, groove, table-board, etc. In many practical applications, the problem of control etched surface morphology is the greatest importance, and production of smooth, defect-free silicon surface is essential for device. The study of anisotropic etching is propitious to get more complex MEMS structuresThe lithography experiment is around BN 303-30 photoresist. Different baking condition and thickness of photoresist result in different photoresist characteristic parameters. Experiment showed that the cause for failure is photoresist formed pinhole with underexposure on the condition of specific thickness. But overexposure caused negative effects of lithography. For the lithography, characteristic parameters depended on its specific experiment.In this paper, the mechanism of wet anisotropic etching of silicon is analysed. On the basis of mechanism, wet anisotropic etching of (100),(110)silicon is studied. In the KOH saturated with isopropyl alcohol solutions, the hydrogen bubbles can easily detach from the etched surface with introducing the IPA. The silicate of surface and IPA can bring about complex reaction then silicate detach from the etched surface, so morphology of surface is improved by this mechanism. The etching process in the presence of IPA is thought to be a permanent competition between IPA particles and OH- ions in settling the reactive surface sites, so the sites with IPA particles cannot weak their backbonds. The reaction is temporary stopped. IPA addition to KOH solution reduce etch rates of (110)-type planes.1, 6-hexanediol and C₂H₅OH addition to KOH solution is propitious to silicate and hydrogen bubbles detaching from the etched surface. The adsorption to Si(110) surface is limtted which can't strengthen anisotropic of wet etching. Si(110) morphology is improved by inctrducing 1,6-hexanediol and C₂H₅OH to KOH solution, under 50vol% KOH conditions, the most smooth surface can be used for structure of MEMS on the silicon substrate.