A Simple Model to Explain High Speed Etching of Silicon in NH2OH-added Alkaline Solutions

Vismaya, K T and Pal, Prem (2019) A Simple Model to Explain High Speed Etching of Silicon in NH2OH-added Alkaline Solutions. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

Anisotropic wet bulk micromachining is a dominant technique used in microelectromechanical systems (MEMS) to fabricate microstructures having applications in sensors and actuators. Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) based solutions are the most commonly used wet anisotropic etchants. However, the etch rate attainable using these conventional etchants is limited and hence affects industrial productivity. Alkaline solutions with some added additives show improved etching characteristics. Addition of NH2OH to pure alkaline etchant solutions increases etch rate significantly. The etch depth attained per unit time is more in these modified solutions compared to pure alkaline solutions. However, the etch rate is found to decrease with etchant age at higher temperature. In this work, the variation of etch rate with etchant age at lower temperature is investigated. The higher etch rate in NH2OH-added alkaline solution can be exploited to make microstructures with low fabrication time and high productivity. A simple model is proposed to explain silicon wet anisotropic etching in NH2OH-added alkaline solutions highlighting the reason behind the increased etch rate.

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