X-RAY PHOTOEMISSION-STUDY OF SF6/O2 TRIODE REACTIVE ION ETCHING OF POLYCRYSTALLINE SILICON, SILICON DIOXIDE, AND THEIR INTERFACE

Surface and interfacial residue films formed on polycrystalline silicon, silicon dioxide, and the interface between polycrystalline silicon on SiO2 by reactive ion etching with SF6/10%O2 at 100 mTorr have been investigated using x-ray photoemission spectroscopy. Reactive ion etching residue films produced in a simple diode reactor and in a triode reactor operated with the electrodes powered in phase and 180-degrees ou of phase were compared. In-phase excitation of the triode produced the lowest etch rate cf polycrystalline silicon and SiO2 and the highest selectivity. 180-degrees out-of-phase excitation produced the highest etch rates and lowest selectivity. The diode performed in between the triode configurations. Surface residue film thickness and composition on polycrystalline silicon and SiO2 appear rate dependent. Composition and chemistry at the surface and the interface are variations of Si (OF)x. In the case Of SiO2, the high etch rate of the 180-degrees out-of-phase excited triode reactor produced a SiF-like species that may be a percursor to the formation of Si(OF)x. The highest etch rate produces the thinnest surface residue film thickness. At the interface, the 180-degrees out-of-phase excited triode produced the most abrupt interface ( < 150 angstrom). The diode and 0-degrees in-phase excited triode produced increasingly large interfacial widths that may be interpreted as etch nonuniformities over a 3X3 mm2 analysis area.