Speaker: Petros Thomas
Title: Carbonaceous Contamination on Extreme Ultraviolet Lithography Mirrors Due to Different Wavelengths of Light
Abstract: Extreme Ultraviolet Lithography (EUVL) is one the leading candidates as the next generation of lithographic technology for the semiconductor industry. One of the challenges of EUVL is the carbonaceous contamination of the multilayer EUV mirrors in the tool which reduces the reflectivity of the mirrors in the desired wavelength range. Carbonaceous contamination on optical surfaces due to light in hydrocarbon environment is a major problem in different applications such as synchrotron beam lines, astronomy telescopes, and recently in EUV lithography. Although the problem has been around for a long time, the basic mechanism of the contamination is still not fully understood. The contamination is localized to the region of the surface exposed to light in the presence of hydrocarbons. The hydrocarbons dissociate and leave carbonaceous film in the exposed region of the surface. Whether the dissociation of the hydrocarbons is caused by the incoming photons of the light or secondary electrons from the surface is not well known.
Using a Xe-plasma source which emits not only the desired wavelength near 13.5 nm (EUV light) but a wide range of out-of-band (OOB) wavelengths extending as far as the visible region, we studied the carbonaceous contamination rates of different wavelength regions. We have measured the wavelength dependence of carbon contamination on a Ru-capped mirror. These results are compared to contamination rates on TiO2 and ZrO2 capping layers.