Monarch Hydrofluoric (HF) Vapor

The SPTS Monarch is a single-wafer vapor-phase hydrofluoric (HF) etcher designed for processing 200 mm (8-inch) wafers. The tool operates with a specified temperature range of 35 °C to 70 °C, a chamber pressure range of 50 Torr to 250 Torr, HF flow rates from 50 sccm to 1000 sccm, and ethanol flow rates from 0.1 ml/min to 1 ml/min.^[1]

Vapor HF etching uses anhydrous HF gas delivered into a heated, low-pressure chamber. A controlled flow of an alcohol vapor, typically ethanol, is added to act as a catalyst and a source of water for the reaction. The HF and ethanol react on the wafer surface to form a thin layer of diluted hydrofluoric acid that etches silicon dioxide, while the volatile byproducts are pumped away.

Vapor HF etch tools are used after silicon dioxide deposition steps or before critical release processes in MEMS fabrication. The tool fits in a fab's etch module where dry, isotropic oxide removal is needed without introducing moisture or particle contamination.

The primary application of vapor HF etching is the release of microelectromechanical systems (MEMS) structures, such as accelerometers, gyroscopes, and pressure sensors. The dry process eliminates stiction caused by capillary forces in liquid etching.

Other applications include the removal of sacrificial oxide layers in advanced packaging, cleaning of oxide residues after plasma etching, and selective oxide removal in front-end-of-line processes where damage to active layers must be minimized.