EXTREME ULTRAVIOLET LITHOGRAPHY (EUVL) ALTERNATING PHASE SHIFT MASK

An alternating phase shift mask for use with extreme ultraviolet lithography is provided. A substrate with a planar top surface is used as a base for the phase shift mask. A spacer layer serves as a Fabry-Perot cavity for controlling the phase shift difference between two adjacent surfaces of the phase shift mask and controlling the reflectivity from the top of the second multilayer. A protective layer serves as an etch stop layer to protect a first multilayer region in certain regions of the phase shift mask, while other regions of the phase shift mask utilize a second multilayer region for achieving a phase shift difference. Some embodiments may further include an absorber layer region to provide areas with no reflectance, in addition to the areas of alternating phase shift. Embodiments of the present invention may be used to monitor the focus and aberration of a lithography tool.