Adhesion and removal behavior of particulate contaminants from EUV mask materials

Abstract

This study investigates the effect of the adhesion and removal of particles such as silica (SiO2), tantalum (Ta) and polystyrene latex (PSL) from three different kinds of EUV (extreme ultra violet) mask surfaces, specifically silicon (Si), tantalum nitride (TaN), and ruthenium (Ru). The results show that inorganic particles such as silica and Ta deposited on Si surface are harder to remove from its surface than from TaN and Ru surfaces. This is due not only to the presence of van der Waals forces but also the hydrogen bonding force between them. On the other hand, an organic contaminant such as PSL particles deposited on Si is easily removed from the surface. This is due to the presence of van der Waals forces between the surface and particles. Inorganic particles deposited on a Ru surface are easily removed from its surface compared with a Si surface. However, PSL particles deposited on a Ru surface are hard to remove due to the presence of pi bonding between the Ru surface and the PSL particles. To weaken the chemical bonding (pi bond), a tetramethylammonium hydroxide (TMAH) cleaning solution is used to improve the removal efficiency of PSL particles on the Ru surface.