Cleaning aluminum fluoride coatings from plasma reactor walls in SiCl4/Cl2plasmas

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. AlF x coatings are formed on the reactor walls as soon as the Al 2 O 3 reactor walls are exposed to fluorine (F)-based plasmas. Since plasma reactors are always cleaned in fluorine chemistries, SF 6 for example, AlF x formation is inevitable in the typical plasma clean conditions used in manufacturing. AlF x 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 AlF x and we report that SiCl x radicals/ions etch AlF x material by forming AlCl x and SiF x products. By using a dedicated technique based on x-ray photoelectron spectroscopy to analyze the reactor walls, we show that AlF x (and also YF x ) coatings formed on the reactor walls are cleared in SiCl 4 /Cl 2 plasmas, restoring clean Al 2 O 3 (Y 2 O 3 ) 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, SiCl 4 -based plasma chemistries efficiently remove other metal fluorides (such as HfF x ) and more generally metallic oxides (high- k ) from the reactor walls.