material can be any material that transmits to be used light wavelengths while at the same time serving as an etch stop material that is a material that selectively does not etch when the layer above is being etched etch stop material 70 is preferably formed using physical vapor deposition or chemical vapor deposition at a temperature selected to avoid flowing or other modification to the underlying reflector 60 structure fig2 illustrates a mechanism for determining the appropriate thickness of etch stop material 70 fig1 in the case of silicon dioxide a chart is plotted to show the relationship between silicon dioxide thickness and underlying reflector reflectivity at euvl wavelengths assuming an incident light beam angle of 5 degrees the thicker the silicon dioxide the less reflectivity preferably a thickness of about 2 nanometers is used for etch stop material 70 if it is silicon dioxide a thin layer of silicon dioxide can be formed by oxidation if there is an underlayer of silicon material fig3 represents a cross sectional view of the step following formation of etch stop layer 70 which is formation of a structural layer 80 in this embodiment structural layer 80 is amorphous silicon formed from physical vapor deposition or chemical vapor deposition the material for structure layer 80 is chosen for properties of being selectively etchable relative to etch stop layer 70 if etch stop layer 70 is silicon dioxide structure layer 80 is appropriately amorphous silicon another advantage to using amorphous silicon in the case of euvl is that it is substantially transmissive to euvl wavelengths at relatively large thicknesses on the order of 1000 to 1500 angstroms with a substantially transmissive structure layer 80 structure layer 80 can remain as part of the overall mask structure and not be.