Thermal and photochemical promotion of silicon and silicon dioxide etching by carbonyl difluoride

Abstract
Silicon (111) surfaces that were cleaned and characterized in ultrahigh vacuum were exposed to carbonyl difluoride. After adsorption of COF2, the silicon crystal was heated to 625 °C resulting in a surface etching reaction as evidenced by the desorption of silicon tetrafluoride. Si(111) surfaces covered with a native oxide layer were also exposed to carbonyl difluoride. Dissociation of COF2, using high fluences from the CO2 laser, caused etching of the SiO2 surface. Volatile SiF4(g) was detected by transmission Fourier transform infrared spectroscopy. Two mechanisms, for the thermally enhanced etching of silicon by COF2 and the photochemically promoted etching of silicon dioxide by COF2, are proposed.

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