Method to Evaluate the Influence of Etching Damage on Microcantilever Surface on Its Mechanical Properties

We propose a method to evaluate the effect of process damage on microcantilever surfaces, introduced by processes such as plasma etching, on their mechanical properties. Using this method, we can compare the mechanical properties before and after etching even if the process changes the microcantilever thickness. Defects at the microcantilever surface affect the quality ($Q$) factor of the microcantilever, but the $Q$ factor cannot be used as an indicator to evaluate process damage because it also depends on the microcantilever thickness. On the basis of theoretical considerations, we propose using $Q/f$ ($f$: resonance frequency) as an indicator because both $Q$ and $f$ are proportional to the thickness for very thin microcantilevers. We verified our method experimentally by etching microcantilever surfaces using conventional plasma etching and neutral beam etching, which can etch silicon without damage. As a result, the $Q/f$ value markedly decreased after plasma etching but stayed nearly the same after neutral beam etching.