Etching is a key process in MEMS fabrication. After lithography defines the pattern, etching selectively removes materials to transfer the design into the substrate or film layer. The etching result directly affects structural accuracy, sidewall profile, release quality and device performance.

MEMS etching can generally be divided into dry etching and wet etching. Dry etching uses plasma, ions or reactive species to remove materials. RIE provides anisotropic profiles for fine structures, while DRIE and the Bosch process can form deep, high-aspect-ratio silicon structures. These processes are widely used in inertial sensors, pressure sensors and microfluidic devices.

Wet etching uses chemical solutions to remove selected materials. It offers low cost, simple operation and high throughput. It is often used for sacrificial-layer release, bulk silicon micromachining and material-selective removal. However, wet etching may suffer from undercut and lower profile control, so it must be carefully matched with device requirements.

Important process parameters include etch rate, selectivity, uniformity, anisotropy, surface roughness and mask durability. For MEMS devices, stress, release behavior, stiction and surface damage must also be considered.

Etching supports the fabrication of cavities, membranes, cantilever beams, comb fingers, microchannels and through-wafer structures. In many MEMS products, dry and wet etching are combined to achieve both precision and efficiency.

As MEMS devices become smaller and more complex, etching technologies will continue to develop toward higher aspect ratios, lower damage, better profile control and improved compatibility with new materials and wafer-level integration.