Dynamics of H atoms surface recombination in low-temperature plasma

Abstract

The dynamics of H atom recombination on materials of interest for a EUV lithographer was studied under a long-term low-pressure H2 plasma exposure. The similarity of the experimental plasma with the typical EUV-induced plasma over the multilayer mirrors surface of the EUV lithographic machine is demonstrated by means of 2D PIC MC simulation. The measurement of the temporal dynamics of the H atom surface loss probability (γH) is chosen for testing the surface modification during the treatment. Time-resolved actinometry of H atoms with Kr as the actinometer gas was used to detect the dynamics of the H-atom loss probability on the surface of Al, Ru, RVS, and SiO2. It is demonstrated that significant changes of the materials surface occur only at the very beginning of the treatment and are due to surface heating and cleaning effects. After that no changes in the γH are found, indicating that the surface stays absolutely stable. A special test of sensitivity of the used method to the state of surface was carried out. Dynamics of the γH changes with small O2 addition clearly demonstrate modification of the Al surface due to oxidation with the next removal of oxygen by the H2 plasma treatment. The rate of oxide removal is shown to be determined by plasma parameters such as the ion energy and flux to the surface.