Comparison of carbon cleaning mechanisms in EUV-induced and SWD plasmas in H2 and He environments

Optics contamination with amorphous carbon (a-C) remains one of the challenges in extreme ultraviolet (EUV) lithography. Processes of a-C removing from Si surface under two kinds of plasma influence in two different gas environments were studied. Carbon-cleaning mechanisms in H2 and He environment were studied with the help of two different experimental setups. Cleaning efficiency in two types of experiments (EUV-induced plasma vs surface wave discharge (SWD) plasma) in two different gases (H2 vs He) were estimated. It was observed, that cleaning efficiency for He in both plasmas are close (sputtering) but cleaning efficiency for H2 in EUV plasma few times higher then in SWD plasma. The supposed explanation can be connected with activation of a surface by EUV photons due to that hydrogen can be absorbed and interacts with it more effectively. For those reason the C cleaning mechanism in EUV-induced plasma could be characterized as a new mechanism and named «EUV-reactive ion etching.