Method to remove Mo/Si multilayers without damaging starting substrate
Original Publication Date: 2002-May-31
Included in the Prior Art Database: 2002-May-31
Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor (SEMI Standard P-37) that is coated with Mo/Si multilayers. One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. In the case of high defect or damaged multilayers, it is advantageous to recover the starting low thermal expansion material substrate. The starting substrates, due to the required specifications, have a very high manufacturing cost, and a method to recover these substrates without compromising the properties will enable a lower cost for the masks. This document details the method to remove the damaged multilayers from the substrates without compromising the morphology and characteristics of the starting substrate. The invention is also applicable to optical elements of the EUV projection optics system that has reflective Mo/Si mirrors of various shapes.