Adhesion force change on multilayer EUVL mask due to laser induced plasma shock wave

Change in adhesion force between a borosilicate glass microsphere and 40 Al2O3/TaN/Ru/MoSi pairs on a silicon wafer used as a multilayer extreme ultraviolet lithography mask stack were characterized by force–distance spectroscopy after cleaning Al2O3 layers using a laser induced plasma (LIP) shock wave. The adhesion force of the Al2O3 surface decreased at a higher laser energy and a lower gap distance above a threshold gap distance without changes in surface roughness. Frictional electrostatic repulsion, triboelectricity, was identified as the cause of lower adhesion forces on Al2O3 surface due to the high velocity and pressure of the LIP shock waves. The adhesion force decreased by increasing the number of exposures of LIP shock waves to the substrate.