A systematic study of the etching characteristics of Si{111} in modified TMAH

Wet bulk micromachining on Si{111} is done to fabricate simple to complex microstructures for applications in sensors and actuators. In this work, it has been performed a systematic study of Si{111} in modified 5 wt% tetramethyl-ammonium hydroxide (TMAH) with varying concentration of NH2OH for achieving improved etching characteristics especially high lateral undercutting at mask edges aligned along non-〈110〉 directions. The concentration of NH2OH is varied from 5 to 20% in step of 5%. The lateral undercutting, which is highly desirable for the quick release of freestanding microstructures from the substrate, is increased considerably with the addition of NH2OH in TMAH solution. In addition, the incorporation of NH2OH improves etched surface morphology. Moreover, the effect of etchant ageing on the etching characteristics is investigated. Suspended microstructures are fabricated to demonstrate the application of modified TMAH solution for silicon wet bulk micromachining. The results presented in this work are highly useful where Si{111} wafer is used for the fabrication of microstructures.