Paper PS-TuM13
Remote Shielded Microwave Mini Plasma Source for Sample Cleaning

Tuesday, October 20, 2015, 12:00 pm, Room 210B

In EUV contamination control, but also more generally, there is a desire for a cleaning technique that can remove hydrocarbon contaminants without inflicting damage to the underlying substrate, e.g. in electron microscopy. Plasma cleaning based on shielded microwave using hydrogen is such a cleaning technique. Generally microwave plasma cleaners are quite big, but at TNO we are pursuing miniaturized plasma cleaners to enable local in-situ cleaning.

In an earlier attempt a mini plasma cleaner has been developed based on a resonant cavity partially filled with a high dielectric material. The source could be operated inside a vacuum system. Due to unexpected thermal issues the source operated only a limited number of times. Furthermore we experienced that it was difficult to judge from the outside why the plasma source was not igniting anymore. A desire for detailed diagnostics during plasma ignition attempts was evident.

A second generation mini microwave plasma cleaner was subsequently designed, built, and tested. The aim was to realize a mini plasma cleaner that should fit on small load locks. Thus substrate could be cleaned prior or after an inspection/processing step. A microwave test setup was designed that allowed simultaneous supply of high power microwave signal at a fixed microwave frequency, for ignition of the plasma, and supply of a low power swept microwave frequency signal for resonator characterization.

This presentation will focus on realization and characterization of the mini plasma source. Cleaning rate as well as detailed microwave characterization measurements have been performed. The microwave measurements demonstrated in real time the effect of plasma ignition on resonance behavior of the cavity.