Fabrication Of A Silicon Micromachined Capacitive Microphone Using A Dry-etch Process

Capacitive microphones are fabricated using etch-release of sacrificial silicon by an isotropic dry etchant. The process allows the production of a microphone largely from CVD processes with flexibility in materials selection. The dry etch chemistry does not require freeze-drying after release. The etchant does not attack electrodes or metallized circuitry and so allows the placement of the electrodes between the backplate and diaphragm dielectric layers. Diffusion barrier layers between the sacrificial and electrode layers protect both materials from interdiffusion during device fabrication. The process is especially fitting for a microphone comprising silicon nitride dielectric layers with aluminum electrodes.