Protection layer on low thermal expansion material (LTEM) substrate of extreme ultraviolet (EUV) mask

A method of fabricating a photomask, comprising:

• forming a plurality of multilayers of reflecting films over a top surface of a substrate;
• forming a capping layer over the plurality of multilayers of reflecting films;
• forming an absorption layer over the capping layer;
• forming a first photoresist layer over the absorption layer;
• patterning portions of the first photoresist layer and the absorption layer to form first openings in the absorption layer, wherein the first openings expose portions of the capping layer;
• removing remaining portions of the first photoresist layer;
• forming a second photoresist layer over portions of the absorption layer, wherein the second photoresist layer covers at least the first openings;
• patterning portions of the absorption layer and the capping layer and the plurality of multilayer of reflecting films not covered by the second photoresist layer to form second openings in the absorption layer, wherein the second openings expose portions of the substrate;
• forming a protection layer inside the second openings and in direct contact with exposed portions of the substrate, wherein
• the protection layer includes side portions that contact sidewalls of the second openings, and a bottom portion that directly contacts the exposed portions of the substrate,
• the protection layer protects the substrate against an extreme ultraviolet (EUV) irradiation, and
• a vertical extent of the side portions of the protection layer from the bottom portion is less than a combined vertical extent of the plurality of multilayer of reflecting films, the capping layer, and the absorption layer;
• and
• removing the second photoresist layer.

A method of fabricating a photomask, comprising:

• forming a plurality of multilayers of reflecting films over a top surface of a substrate;
• forming a capping layer over the plurality of multilayers of reflecting films;
• forming an absorption layer over the capping layer;
• forming a first photoresist layer over the absorption layer;
• patterning portions of the first photoresist layer and the absorption layer to form first openings in the absorption layer, wherein the first openings expose portions of the capping layer;
• removing remaining portions of the first photoresist layer;
• forming a second photoresist layer over portions of the absorption layer, wherein the second photoresist layer covers at least the first openings;
• patterning portions of the absorption layer and the capping layer and the plurality of multilayer of reflecting films not covered by the second photoresist layer to form second openings in the absorption layer, wherein the second openings expose portions of the substrate;
• forming a protection layer inside the second openings and in direct contact with exposed portions of the substrate, wherein
• wherein the protection layer includes (1) a bottom portion in direct contact with and covering the exposed portions of the substrate, and (2) side portions in direct contact with the sidewalls of the second openings formed by the absorption layer, the capping layer, and the plurality of multilayer of reflecting films,
• a vertical extent of the side portions of the protection layer from the bottom portion thereof is less than a combined vertical extent of the plurality of multilayer of reflecting films, the capping layer, and the absorption layer, and
• the protection layer protects the substrate against an extreme ultraviolet (EUV) irradiation;
• and
• removing the second photoresist layer.