The Lam 4420 is a plasma etcher for the patterning of polysilicon layers, silicon nitride, and selected metals. It also has O2-chemistry available for resist trimming and descumming operations. The powered upper electrode produces a chemical etch process, with very little physical bombardment unlike many RIE etchers. Anisotropy is obtainable through mainly chemical methods involving polymer and etch product redeposition. Likewise, the etch processes can be tuned to achieve very high selectivity through plasma chemistry.
Process conditions and specifications
Pressure 300-500 mT, Power 300 tp 500 W
Poly Si etch: 300-400 nm/min, oxide 15 nm/min, resist 150 nm/min (precise values vary with sidewall profile)
Nitride etch: 300 nm/min, oxide 130 nm/min, resist 500 nm/min
silicon nitride, poly-silicon, TiW, Molybdenum, SiO2, Photoresist
Gases and chemicals
Cl2, CF4, He, O2, SF6, HBr
Trained personnel only can open the etch chamber due to the Cl and Br chemistry
This tool has a mechanical clamp so wafers must have a standard 56 mm primary flat. Secondary flats will be covered by an oversized ring. As a result of this ring, the edge of the wafer will not be etched. The size of the edge exclusion is yet to be determined for the oversized clamp rings. Dedicated recipes with optimised parameters are used for thin wafers.