Cleaning aluminum fluoride coatings from plasma reactor walls in SiCl4/Cl2 plasmas

The formation of aluminum fluoride layers on the inner part of plasma reactor walls is known to be a serious issue for plasma etching processes: it causes process drifts and particle generation. AlFx coatings are formed on the reactor walls as soon as the Al2O3 reactor walls are exposed to fluorine (F)-based plasmas. Since plasma reactors are always cleaned in fluorine chemistries, SF6 for example, AlFx formation is inevitable in the typical plasma clean conditions used in manufacturing. AlFx material being extremely etch resistant, it cannot be removed from reactor walls: it accumulates until particles flake off, then imposing a wet clean of the plasma reactor. In this paper, we review the different methods to reduce or eliminate the formation of AlFx and we report that SiClx radicals/ions etch AlFx material by forming AlClx and SiFx products. By using a dedicated technique based on x-ray photoelectron spectroscopy to analyze the reactor walls, we show that AlFx (and also YFx) coatings formed on the reactor walls are cleared in SiCl4/Cl-2 plasmas, restoring clean Al2O3 (Y2O3) walls before processing the next wafer. As a result the wafer-to-wafer reproducibility and the mean time between reactor wet cleans are probably significantly improved. Furthermore, SiCl4-based plasma chemistries efficiently remove other metal fluorides (such as HfFx) and more generally metallic oxides (high-k) from the reactor walls.