Extreme ultraviolet lithography process and mask with reduced shadow effect and enhanced intensity

An extreme ultraviolet (EUV) mask, comprising:

• a low thermal expansion material (LTEM) substrate;
• a first reflective layer above a surface of the LTEM substrate;
• and
• a second reflective layer over the first reflective layer, wherein the second reflective layer has various openings that define a first state and a second state,
• wherein the first state includes the first reflective layer and is free of the second reflective layer, and the second state includes both the first and second reflective layers,
• wherein the first state has a first reflection coefficient and a first reflectivity, the second state has a second reflection coefficient and a second reflectivity, a phase difference between the first and second reflection coefficients is about 180 degrees, and the second reflectivity is greater than 50% of the first reflectivity.

An extreme ultraviolet (EUV) mask, comprising:

• a low thermal expansion material (LTEM) substrate;
• a first reflective layer above a surface of the LTEM substrate;
• a buffer layer above the first reflective layer;
• and
• a second reflective layer above the buffer layer, wherein the second reflective layer has various openings that define a first state and a second state, wherein the first state includes the first reflective layer and is free of the second reflective layer, and the second state includes both the first and second reflective layers,
• wherein the first state has a first reflection coefficient and a first reflectivity, the second state has a second reflection coefficient and a second reflectivity, a phase difference between the first and second reflection coefficients is about 180 degrees, and the second reflectivity is greater than 50% of the first reflectivity.