Impact of fabrication technology on flexural resonances of silicon nitride cantilevers

Abstract

Impact of fabrication technology on resonant behaviour of LPCVD silicon nitride cantilevers is studied using an optical deflection setup. Two different release techniques are compared, i.e., isotropic dry etching in an SF 6 plasma and wet etching in KOH. The silicon nitride thickness varies between 100 and 680 nm. Dependency of resonance frequencies on length and undercut is studied for both release methods using Euler–Bernoulli beam theory. The wet release method introduces a negligible undercut compared to the dry method. We find that the undercut effectively makes the cantilever longer by a value Δ L, which depends on the undercut distance but which is independent on cantilever length for the samples studied. We have also extracted the Young’s modulus from the resonance frequency vs. length dependency and compared the values of both release methods. The wet release method consistently shows a lower Young’s modulus.