Study on fluorine incorporation during etch step for HDP-CVD oxide gap-filling of nano-scale shallow-trench isolation

For gap-filling of nano-scale shallow trench isolation (STI) with no voids in high-density plasma chemical vapor deposition (HDP-CVD), an etch gas containing NF₃ in the continuous deposition/etch or cyclic deposition-etch-deposition (DED) processes has been adopted and in turn its use has led to fluorine incorporation. Since F incorporation observed during the gap-fill process is known to affect the post-process after gap-fill, a control and an understanding of fluorine incorporation in the etch step is required. Fluorine incorporation in the HDP-CVD oxide was investigated by varying the NF₃/O₂ and the NF₃/Ar plasma conditions during the etch step in the reactive ion etching (RIE) and the chemical dry etching (CDE) modes. As the flow ratio of NF₃ gas was increased, the fluorine incorporation increased. As a result of the increased F incorporation with increasing NF₃ flow ratio, wet etch rates of plasma-etched HDP oxides increased.