Mechanism of the Slow-Down of the Silicon Etch Rate by a Fluorocarbon Overlayer in CF₄/H₂ Reactive Ion Etching of Silicon

We have utilized an ultrahigh vacuum surface analysis system interfaced via a load-lock to a flexible diode dry etching apparatus to study vacuum transferred CF₄/H₂ reactive ion etched silicon surfaces by X-ray photoemission spectroscopy (XPS). From the observation and analysis of silicon-fluorine bonding underneath the fluorocarbon film and the dependence of the abundance of fluorosilyl species on the thickness of the fluorocarbon overlayer, the role of the fluorocarbon film in the slow-down of the Si etch rate has been elucidated: The role of the fluorocarbon film is to “protect” the Si surface from attack of fluorine, rather than prevent the escape of SiF₄ etch product.