Method of critical dimension control by oxygen and nitrogen plasma treatment in EUV mask

An mask for patterning a semiconductor wafer, the mask comprising:

• a substrate;
• a reflective multilayer disposed on the substrate;
• a capping layer disposed on and interfacing with the reflective multilayer;
• and
• an absorber layer disposed on and interfacing with the capping layer, wherein the absorber layer includes a first metal oxide having a first concentration at an interface between the capping layer and the absorber layer and a second concentration at an upper surface of the absorber layer, the second concentration being different than the first concentration.

A method comprising:

• receiving a mask that includes a substrate, a reflective multilayer on the substrate, a capping layer on the reflective multilayer, and an absorber layer on the capping layer;
• patterning the absorber layer to form a trench within the absorber layer, wherein the trench has a first width;
• treating the mask with a first gas to modify the trench to have a second width that is different than the first width;
• and
• treating the mask with a second gas to modify the trench to have a third width that is different than the second width, the second gas being different than the first gas.