Tailoring Anchor Etching Profiles During MEMS Release Using Microfluidic Sheathed Flow

Many MEMS release processes rely on isotropic etches, which can result in the formation of nonideal anchor profiles for optimal device performance. Using microfluidic sheathed flow to generate anisotropic etch characteristics using isotropic etchants, a wet etch process is demonstrated and analyzed to overcome the problem of accurately defining support anchors during wet release. This process allows spatially targeted delivery of process chemicals on a wafer and real-time control of etch profiles using sheath flow confinement. To demonstrate the process, a reusable polydimethylsiloxane three-input microfluidic device was used to release an array of silicon nitride micromachined beams on a porous silicon sacrificial layer. The microstructure anchors were defined by a flow-defined mask that is alterable in real time, creating anchor geometries not achievable by conventional isotropic release methods.