Comparison of H₂and He carbon cleaning mechanisms in extreme ultraviolet induced and surface wave discharge plasmas

Abstract

Cleaning of contamination of optical surfaces by amorphous carbon (a-C) is highly relevant for extreme ultraviolet (EUV) lithography. We have studied the mechanisms for a-C removal from a Si surface. By comparing a-C removal in a surface wave discharge (SWD) plasma and an EUV-induced plasma, the cleaning mechanisms for hydrogen and helium gas environments were determined. The C-atom removal per incident ion was estimated for different sample bias voltages and ion fluxes. It was found that H 2 plasmas generally had higher cleaning rates than He plasmas: up to seven times higher for more negatively biased samples in EUV induced plasma. Moreover, for H 2 , EUV induced plasma was found to be 2-3 times more efficient at removing carbon than the SWD plasma. It was observed carbon removal during exposure to He is due to physical sputtering by He + ions. In H 2 , on the other hand, the increase in carbon removal rates is due to chemical sputtering. This is a new C cleaning mechanism for EUV-induced plasma, which we call "EUV-reactive ion sputtering."

Characterization of carbon contamination under ion and hot atom bombardment in a tin-plasma extreme ultraviolet light source

“…A new cleaning strategy that uses the plasma, induced by EUV ionization of the low-pressure gas (usually H 2 ) over the mirror surface, was recently proposed [9]. This inline cleaning process has the potential to increase the duty cycle of EUVL.…”

Effects of discharge voltage on the characteristics of a-C:H films prepared by H-assisted Plasma CVD method

“…With the density of a-C films of 1.9 g·cm -3 [42,43], the mass density dependence of hydrogen atom density calculated according to Eq. (3) is shown in Fig.…”

Extreme ultraviolet (EUV) source and ultra-high vacuum chamber for studying EUV-induced processes

“…Previous research has demonstrated that MLMs may lose their reflectivity due to their surfaces becoming contaminated with amorphous carbon or surface oxidation, induced by intense EUV radiation [4,5]. One solution that is currently under investigation is using EUV-induced plasma for in-line cleaning [6]. Experiments have shown that carbon etching can be achieved under certain conditions, but the physics and chemistry of the etching process is still not fully understood.…”