Interferometry for end point prediction during plasma etching of various structures in complementary metal–oxide–semiconductor device fabrication

We present results of an interferometric end point prediction technique for use in plasma etching of various gate and localized oxidation of silicon (LOCOS) structures in advanced complementary metal–oxide–semiconductor device fabrication. Etch experiments were carried out in a production high-density plasma source (decoupled plasma source) reactor made by Applied Materials. The end point prediction technique has been applied successfully to many samples and types of structures commonly found in integrated circuit manufacturing. These include: doped and undoped polysilicon material; patterned and unpatterned wafers; flat and topographic surfaces; resist and hard-mask patterned wafers with oxide underlayers of various thicknesses; and product wafers with varied pattern density. The ability to predict endpoint and avoid breakthrough of gate oxides as thin as 19 Å has been investigated. The end point detection system has also been shown to be effective in other etch processes including LOCOS etch, where the end point of the $Si3N4$ etch on the underlying $SiO2$ must be triggered as early as possible to avoid excessive oxide loss or etching of the Si substrate. The flexibility of the end point algorithm together with the external trigger controller are demonstrated to be crucial for successful end point prediction.