uEtch or “yoo-etch” is a HF gas etching tool. Standard wet chemical HF etching can cause "stiction" by pulling the free moving microstructures together which remain adhered to each other after release, reducing device yields.

A gaseous etchant penetrates smaller features more easily and allows longer undercuts.

Alcohol (A) ionises the HF vapor and acts as a catalyst:

SiO₂ (s) + 2HF₂^- (ads) + 2AH⁺ (ads) → SiF₄ (ads) + 2H₂O (ads) + 2A (ads)

The etch process is run at a constant temperature of 45 °C.

Gases: HF, EtOH, N₂.

Key technology benefits:

• Eliminates stiction–repeatable, controlled, low-cost process.
• Compatible with many metals/typical MEMS materials (Al).
• Uses anhydrous HF, semi grade alcohol (ethanol).

Etch rates (isotropic)

• Variable T, P, reagent flows –wide etch rate range.
• 0.05 um/min (dense oxides, small spaces) to >> 1 um/min.
• Maximum rate limited by exposed metals, SiO₂ area and uniformity needs.
• Oxide types (densities), not compatible with doped oxides.
• Not compatible with Cu, Ti, TiO₂