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We report a simple and efficient silicon wet etchant HNA (Hydrofluoric acid, Nitric acid, Acetic acid) for the stiction free release of silicon nitride/metal micro/nanomechanical structures. The HNA concentration was varied with the aim of developing a slow etch rate, which could be utilized to suspend the micron and sub-micron cantilever and fixed beam structures. The etch rate was found to decrease with decrease in HF and increase in HNO3 concentrations. Smooth surface and high selectivity are obtained in case of high HNO3 content. The obtained etchant with a slow etch rate of 440 nm/minute was successfully utilized for the release of silicon nitride cantilevers and fixed beam structures of 500 nm, 2 µm and 5 µm widths with varying lengths. The resonance frequency of suspended cantilevers characterized by Laser Doppler Vibrometer is in close agreement with the COMSOL simulated resonating frequencies proving that the etching process has been precise without changes to cantilever dimensions. In addition, the generated etchant was successfully used in releasing chrome/gold nanobeams as well without any damage to the metal layers.

The major composition of any glass substrates consists of more than 70% silicon dioxide with varying concentration of alkali and alkaline earth metals with minor additives such as Al2O3, B2O3 etc. In this study, glass substrates of different compositions were etched successfully using HF based wet etchants. The etch rate as well as the etched profile is greatly dependent on the composition of the glass substrate being used. Two different composition of glasses, wherein the alkali and alkaline earth metals are in different concentrations were used for the etch profile study. One is Borofloat-33 with no free metal ions and the other is Soda lime glass with free metal ions. The etched profile for Borofloat-33 glass had a partial anisotropy with an inclined angle of 33.7 degree while isotropic etch was obtained with soda lime glass. This anisotropy was maintained for Borofloat-33 glass even after continuous agitation during the etch process. The wet etch selectivity of the glass with respect to stack of a-Si/Cr/Au has been established for ∼106 µm deep etching.