Mask manufacturing method and mask set

A mask manufacturing method comprising:

• providing a first mask including a first antireflection layer, at a first film thickness, stacked on a first pattern layer, a first reflective layer, and a first transmissive substrate;
• providing a second mask including a second antireflection layer, at a second film thickness, stacked on a second pattern layer, a second reflective layer, and a second transmissive substrate, wherein the second pattern layer has a thickness and component equivalent to the first pattern layer but has a different pattern than the first pattern layer, wherein the second reflective layer has a thickness and component equivalent to the first reflective layer, and wherein the second transmissive substrate has a thickness and component equivalent to the first transmissive substrate;
• calculating a first thermal expansion amount of the first mask from a first exposure amount in a first process;
• calculating a second thermal expansion amount of the second mask from a second exposure amount in a second process;
• adjusting the first film thickness and the second film thickness until a difference between the first thermal expansion amount and the second thermal expansion amount is reduced;
• fabricating the first mask including the first antireflection layer, at an adjusted first film thickness, stacked on the first pattern layer, the first reflective layer, the first transmissive substrate;
• and
• fabricating the second mask including the second antireflection layer, at an adjusted second film thickness, stacked on the second pattern layer, the second reflective layer, the second transmissive substrate.